Biogas Book 111711

The Authors: Prof. Jaime Q. Dilidili Dilidili Associate Professor College of Engineering and Info rmation rmation Technology Technology Technology Development Division Head Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University Dr. Dr. Camilo A. P olinga Associate Professor College of Engineering and Info rmation rmation Technology Technology Extension and Promotion Division Head Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University Engr. Rosalie Ararao-Pelle Study Leader Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University

Dr. Dr. Ruperto S. Sang alang University Professor College of Economics, Management and Development Studies Project Leader Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University

The Authors: Prof. Jaime Q. Dilidili Dilidili Associate Professor College of Engineering and Info rmation rmation Technology Technology Technology Development Division Head Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University Dr. Dr. Camilo A. P olinga Associate Professor College of Engineering and Info rmation rmation Technology Technology Extension and Promotion Division Head Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University Engr. Rosalie Ararao-Pelle Study Leader Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University

Dr. Dr. Ruperto S. Sang alang University Professor College of Economics, Management and Development Studies Project Leader Affiliated Aff iliated Renewable Energy Center for Region IV Cavite State University

BIOGAS TECHNOLOGY IN THE PHILIPPINES A Sy nth nt h es is o f Vario Var io us R ea d ing in g s on B iog io g as Tec T ec h no log lo g y

CAVITE STATE UNIVERSITY - AFFILIATED RENEWABLE ENERGY CENTER FOR REGION IV (CvSU-AREC IV) Indang, Cavite, Philippines 2011

First Printing 2011

Philippine Copyright © by CvSU-AREC, 2011 All rights reserved. No parts of this book may be reproduced in any form or by any means without the written permission of the copyright owner. Published and exclusively distributed by the CvSU-AREC Cavite State University Telefax No.: (+6346) 415-0010 email address: [email protected]

ISBN 978-971-9032-67-0

ii

F orew ord The interest in using biogas to address the problem of pollution in the country started in the midsixties. This gained momentum in the midseventies as the government through the Energy Development Board recognized the need to support programs that are aimed at complementing grid based energy. After a series of crash programs, the Department of Energy sought to promote the development and utilization of renewable energy sources in the country in the late eighties by establishing a network of institutions that would specialize in specific renewable energy programs. The Affiliated Non-conventional Energy Center (ANEC) of the former Don Severino Agricultural College, now Cavite State University, was organized and later tasked to specialize in biogas energy. I have been fortunate to head this center since its inception and the national biogas center that was organized under its wing in 1996. The DSAC-ANEC National Biogas Center initiated activities to develop awareness and acceptance of biogas as an energy source with the help of a non-government organization from Japan, the Department of Agriculture and the Department of Energy. After assessing several existing models, the center successfully developed and patented a simplified biogas model which became the focus of several regional and national training programs on biogas. These training programs culminated in the construction of hundreds of biogas installations all over the country. Public and private organizations currently continue to adopt biogas technology as a way of addressing ecological concerns even as the sector also reaps economic benefits from the use of biogas systems. The many years of experience in promoting and establishing biogas systems in the Philippines provided the men and women behind this project with data that served as background material for this book. While no information on topics like this could ever be complete, our team hopes that this book would further encourage our various publics to continue adopting the biogas technology, and to continue looking for ways to improve the operation of biogas systems in the country and, perhaps, elsewhere in the region. If such information as we have included in this book would be able to elicit the interest of even a few on the potentials of using biogas as a viable energy source, our efforts would have been more than compensated.

RUPERTO S. SANGALANG Project Leader, CvSU-AREC

ii i

Acknow ledgment The Cavite State University – Affiliated Renewable Energy Center acknowledges with gratitude the cooperation and assistance of the following institutions and persons in the preparation of the Biogas Technology in the Philippines: A Synthesis of Various Readings on Biogas Technology: Dr. Divinia C. Chavez, President of Cavite State University and Project Director of CvSU-AREC for utmost support in the preparation of this publication; The Department of Agriculture (DA), the Department of Science and Technology (DOST) and the Department of Environment and Natural Resources (DENR) and their sub-units for their assistance in collecting and gathering the needed information; The Department of Energy (DOE) for the financial support in the preparation and printing of this publication, and the DOE ’s regional offices for the provision of valuable information on biogas technology; Prof. Rene Alburo and staff of San Carlos University – AREC for the assistance in the conduct of biogas regional forum for the Visayas and Mindanao regions which also gave way for the CvSU-AREC staff to collect the needed data and visit biogas projects in Cebu; The owners and managers of the different biogas installations especially the management of W ellisa Farms for allowing the CvSU-AREC staff to observe the full operation of the farm and take pictures of the biogas installations; The Philbio for providing list of their biogas projects and other needed information; Dr. Ruperto S. Sangalang, CvSU-AREC Project Leader; Prof. Jaime Q. Dilidili, head of CvSU-AREC Technology Development Division; Dr. Camilo A. Polinga, head of CvSU-AREC Extension and Promotion Division; and Engr. Rosalie A. Pelle, CvSU-AREC Study Leader for the preparation, reviewing and editing the content of the manuscript; and, The present and former staff of CvSU-AREC, namely: Mrs. Gloria L. Martonito and Dr. Elizabeth E. Polinga for editing the manuscript; David F. Almazar for gathering information, preparing plans and estimates and providing pictures needed for the publication; Elmer Matel, Ma. Zobel Caraan, Camille Joy Capupus and Jeffrey Cotoner for assisting in editing, layouting, cover-design, drawing/ illustrations and photographic works; and Engr. Rene Marasigan and Mr. Cielito Pulido for being part of CvSU biogas development projects. iv

Contents

Page

INTRODUCTION

2

CHAPTER I. Historical Development of Biogas Technology

4

Historical Development of Biogas Technology Trends and Advancements of Biogas Technology

CHAPTER II. Biogas Technological Process Biogas Technological Process Stages in Biogas Fermentation Process Classification of Biogas Fermentation Process Factors that Influence Biogas Production

CHAPTER III. Comprehensive Utilization of Biogas Technology Biogas Utilization Sludge Utilization Biogas Technology as Waste-Treatment Facility

CHAPTER IV. Design of Biogas Digester

4 13

18 19 19 21 23

32 32 36 38

40

Design of Biogas Digester According to Form and Structure Advantages and Disadvantages of Various Designs Digester Models in the Philippines

CHAPTER V. DSAC-Model Biogas D igester DSAC-Model Biogas Digester Components of DSAC-Model Biogas Digester Principles of Operation Design Formulas Sizing of Biogas Digester Pre-Construction Consideration Site Consideration

v

40 46 54

56 56 57 58 59 61 62 64

Page Construction Techniques (DSAC-Model Rectangular Fixed-Dome Digester) a. Lay-outing b. Excavation c. Bottom Construction d. Flooring Construction e. Wall Masonry f. Construction of Inlet g. Construction of Hydraulic Tank h.Top Beam Construction i. Dome Construction j. Sealing the Digester k. Air and Water-tightness Tests

CHAPTER VI. Tubular Polyethylene Digester Major Parts of TPED Biogas Digester Installation of TPED Biogas Digester Protection of Polyethylene Plastic Digester and Gas Reservoir Preparation of the Polyethylene Plastic Digester Preparation of Gas Reservoir Methods of Constructing the Biogas System

CHAPTE R VII. Covered Lagoon Digester Covered Lagoon Digester Components of Covered Lagoon Digester Covered Lagoon Design Variables Operation and Maintenance of Covered Lagoon Digester The Covered In-Ground Anaerobic Reactor (CIGAR) CHAPTER VIII. Operation and Maintenance of Biogas Digester Initial Loading Regular Loading Stirring/Agitation of Slurry Condensate Removal Servicing Scum Problem Periodic Maintenance of the Digester

vi

65 65 66 66 66 67 68 68 70 70 72 73

78 78 79 80 81 82 82

86 86 86 87 88 89

94 94 95 96 96 96 97

Page

CHAPTER IX. Biogas Upgrading

100

Biogas Upgrading Determination of the Hydrogen Sulphide Content Biogas Upgrading Techniques Biogas Purification Process by ITDI

CHAPTER X. Benefits from Biogas Technology

100 101 102 107

110

Benefits from Biogas Technology Economic Assessment of DSAC-Model Biogas Digester Cost Component of the Biogas System Energy Value of Biogas

110

CHAPTER XI. Opportunities and Barriers of Biogas Technology

116

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110 111 112

List of F igure s Page Participants of the First National Training Course on Biogas Technology 2 Biogas installations in the Philippines 3 60-seater biogas-fueled train 4 Synergy Biopower Containerized Control Center 5 XC-Series external combustion systems 25kWe-52kWe 6 Record-beating A4, with a maximum speed of 327.2 km/hr (203 mph), runs on biogas 7 Guascor 957 kW engine generator set 8 Biogas purification using pressure swing absorption process 9 The biogas technological process 10 Stages of biogas fermentation 11 The three stages of fermentation 12a Mechanical stirrer 12b Hydraulic stirrer 12c Gas stirrer 13 Comprehensive utilization of biogas technology 14a Biogas stoves/burners 14b Biogas lamp 14c General motors dual-fuel generator sets designed by Don Hardy with power output of 60 to 200 kW 14d Double door refrigerating machine 15a Sludge used as organic fertilizer 15b Liquid sludge is recycled to clean animal pen 16 B iog as t ec hn olog y in w ast ewat er treat men t syst em 17a Fixed-dome digester 17b 1 Top floating gas holder digester 17b 2 Separate floating gas holder digester 17c Bag digester 18 Construction shapes of biogas digester 19 Different orientations of inlet and outlet for design flexibility 20 Ground digester 21 Semi-buried digester 1

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7 12 13 14

15 15 16 16 19 20 20 27 27 28 31 33 33 34 35 37 37 38 41 41 42 42 43 44 45 45

Page 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43a&b 44 45 46a 46b 47a 47b 47c 47d 48a 48b 48c 48d 48e

Underground digester Cylindrical fixed-dome digester Spherical hydraulic digester Ellipsoidal hydraulic digester Flexible bag-type combined digester/holder Two-chamber rectangular digester with floating gas holder Fixed-dome digester with separate gas holder Deenbandhu biogas digester Rectangular/Square fixed dome digester DSAC-Model biogas digester Basic components of a DSAC-Model biogas system Design formulas Planning/Preparation Lay-outing Excavation Bottom construction Flooring construction Wall masonry Construction of inlet Construction of hydraulic tank Top beam construction Dome construction Sealing the digester Water-tightness test Air-tightness test Manometer Lay-out Plan Longitudinal section Section of inlet pipe and hydraulic chamber Concrete trench Trench dug in the ground Digester on top of the ground w/o trench The funnel type entrance of manure with screen protection of digester First model

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46 47 48 48 49 50 51 52 53 56 56 59 62 65 66 67 67 68 69 69 70 71 72 73 74 74 75 76 76 76 79 79 80 81 83

Page 48f 49 50 51 52 53 54 55a 55b 55c 5d 55e 56

Second model Covered lagoon digester CIGAR at Rocky Farm The CIGAR system Lagoon digester and biogas handling URC RF 12 Lagoon effluent Flow diagram for chemical absorption Flow diagram for high pressure water scrubbing Flow diagram for pressure swing absorption Flow diagram for cryogenic separation process Schematic representation of membrane separation Biogas purification process by ITDI

83 86 90 90 91 92 92 105 105 105 106 106 107

List of Tables 1 2 3 4 5 6 7 8 9 10

Preferable retention time and gas production at different temperatures C/N Ratio of some organic materials Potential gas yield of selected raw materials Toxic level of various inhibitors Applications of one cu.m. biogas Mineral composition of sludge Bill of materials for a 6 cu.m. DSAC-Model biogas plant Materials needed for the onstruction of Tubular Polyethylene Digester Troubleshooting of biogas plant Performance efficiency of ITDI scrubber system

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24 25 29 30 36 36 75 84 98 108

Appendices Page APPENDIX A. Utilization of B iogas Sludge as Feed Substitute for Hogs

120

APPENDIX B. W ellisa Farm Waste t o Energy Project

127

APPENDIX C. Biogas Expert/Contractors/Suppliers in the Philippines

137

Appendix Tables 1

2 3 4 5

Monthly average weight of hogs given partly substituted with biogas digester sludge, kg Monthly average gain in weight of hogs given diets partly substituted with biogas digester sludge,% Mean feed conversion efficiency of hogs given diets partly substituted with biogas digester sludge, % Summary of carcass quality evaluation of hogs given diets partly substituted with biogas digester sludge Biogas Experts/Contractors/Suppliers in the Philippines

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124 125 125 126 137

INTRODUCTION The Philippines has 13.46 million pigs and 135.64 million chickens (BAS, 2007). Of the 13 million pigs, 9 million are found in the smallhold raisers because livestock raising is secondary to crop production in terms of agriculture livelihood. The average number of pigs raised in the smallhold sector is about 8 heads where households in the villages augment family income from the sale of pigs. With this number of heads, the total manure production reached to more than 30 thousand tonnes per day. This volume is quite tremendous and if not properly managed will

become the major pollutant of air and water. Management of animal wastes is a big problem in the animal producing areas since very few raisers have biogas digesters. Wastes are allowed to flow freely to open fields, thus emitting foul odors and contaminating surface and underground water. Agriculture (livestock and c rop production) contributed 32%

of the total greenhouse gases emmissions (1994 Philippine GHG Inventory). These greenhouse gases consist of carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2O) and other gases which came mainly from livestock wastes.

Why Biogas Technology?

n

There is a need for low cost waste treatment facility due to the growing animal industry. Waste treatment plus energy generation technology

n

Waste utilization

n

Environment-friendly alternative

n

Biogas technology provides solution to pollution problem being a “waste-treatment facility ” and at the same time an “energy-generating device ”. Biogas Technology in the Philippines

2

Chapter I

HISTORICAL DEVELOPMENT OF BIOGAS TECHNOLOGY History of Biogas Technology in the Philippines Interest in biogas development grew with the encouraging

reports from the official mission of the Philippine Coconut Administration after its return from a European tour in 1965. The main interest in biogas stemmed from its pollution prevention

and public health aspects rather than from its fuel energy generation potential, as firewood was abundantly available then. In

the early 70s, Dr. Felix D. Maramba, an agricultural engineer by profession of the Araneta University Foundation, pioneered the development of biogas technology at Maya Farms, an integrated livestock farm, meat processing and canning operation in the Antipolo Hills of Rizal Province. Demonstration models of Indian, Chinese and European types were set up by the

farm in order to obtain the necessary experience and to assess the suitability of different types of plants. The models were later modified and used as pilot plants. Biogas produced at the farm supplies 40% of the total power requirement of the farm and was used for domestic applications, cooking vats in the canning plant, fuel of burners for heating and gasoline engines running a feed mill, operating a 60-KVA electric generator and running farm vehicles. The late President Ferdinand E. Marcos directed the Energy

Development Board (now Department of Energy) in the later part of 1976 to embark in a crash program to use biogas as substitute fuel.

Biogas Technology in the Philippines

4

He instructed the establishment of model biogas plants in stock farms in every province and towns where there are breeding stations. In the early 80 ’s, as part of the “crash programme”, the Bureau of Animal Industry and the EDB, launched a program on “Biogas ng Barangay” (Village Biogas Project). Loans were made available to livestock owners through financial institutions. Demonstration projects at the regional and provincial levels were

established; 340 units of concrete biogas plant, 321 units in Luzon, 18 in Visayas and 1 in Mindanao. Available fresh pig manure per year was estimated at 8.9 million tons, indicating a biogas production potential of 502 million cubic meters per year. The Indian design with a floating gas holder was more popular. The model did not last long because of the maintenance problem.

Due to lack of government support on the technology and the series of reorganization in the government, the continuity and prioritization of the project became less important. Other organizations engaged in extension of biogas technology were the National Housing Authority, the Engineering Battalion of the military, and the Department of Community Development. The Development Bank of the Philippines granted loans to farmers at low interest rates for the biogas projects. The Philippine Rural Life Center (PRLC), a non-government organization promoted a culvert model b iogas system in the early

80s. The PRLC trained people from the government as well as private sectors in the field of animal production and biogas technology. Many units of the model were copied and installed in some selected villages but the continuity ceased because the PR LC

project was also terminated in the late 80 ’s. Also in the late 80 ’s, the Affiliated Renewable Energy Centers (ARECs - formerly ANEC) were established at different state colleges and universities nationwide to serve as extension arm of the Department of Energy (DOE) in promoting renewable energy in the rural areas.

5


The Cavite State University (CvSU), formerly Don Severino Agricultural College (DSAC) was very active in the development of the design especially for semi-commercial pig raisers. CvSU-AREC: Revitalize Biogas Technology

Cavite State University – Affiliated Renewable Energy Center (CvSU-AREC) was established in 1989 by the Department of Energy (DOE) in its efforts to promote the use of Renewable Energy Technologies (RETs) in Region IV. There were other ARECs established in several strategically located colleges and universities (both private and public) in other regions of the country

to serve as DOE ’s extension arm to the rural areas. During the first few years of the project, information awareness campaigns were conducted to promote the use of Renewable Energy resources such as wind, hydro, solar and biomass. The Center was successful in arousing the interest of the people in the livestock sector but not so successful in convincing

them to invest in any of these technologies mainly because of the availability of grid electricity in their area and most clients lack needed capital and they were used to receiving dole out projects from the government. In the 90’s, pig production in the Philippines rapidly grew,

but gained negative impact due to significant environmental problems brought by the industry. Being aware of these, the CvSU-AREC team reassessed its position and focused its thrust on BIOGAS TECHNOLOGY, a decade old technology which offers energy generation and environmental protection. Seminars and trainings on biogas technology were attended by AREC staff and a number of working models were constructed to obtain an indepth knowledge of the technology.


6

A major opportunity for additional knowledge came in September 1991 when STET, an NGO from Japan, sponsored the three-month hands-on training on Biogas Technology at the Biogas

Research and Training Center for Asia and the Pacific (BRTC) in Chengdu, People’s Republic of China, which was participated in by Prof. Jaime Q. Dilidili, head of the Technology Development Division of the CvSU-AREC. This was followed in November 1991 by a 45-day hands-on training sponsored by the International Institute for Rural Reconstruction (IIRR) with Indian technician as trainors. Since then, the center ’s capability was strengthened and enhanced. These trainings enabled the AREC staff to fully understand the principles and processes of Biogas Technology, which eventually facilitated the transfer of knowledge and expertise to more than a hundred clienteles. In 1993, the First National Training Course on Biogas Technology was conducted at the then Don Severino Agricultural College with the primary objectives of promoting the technology and producing skilled biogas technician to construct and supervise

the construction of a biogas plant.

Figure 1. Participants of the First National Training Course on Biogas Technology 7


A Chinese Biogas Digester Model was also designed and constructed at the CvSU main campus for validation purposes. In the course of evaluation, its performance was subjected to necessary adjustments to make it an effective working model. Difficulties were encountered in the replication of the same model

and the transfer of the technology in the absence of highly specialized skills for that purpose. It was at this point that the Center designed a simple model which is adaptable to Filipino masonry skills, easy to construct and readily operational. Thus, the birth of DSAC-Biogas Digester Model which was awarded by the Intellectual Property Office (IPO) a Utility Model Registration Number UM 2-1997-15098 on April 9, 2002. The National Biogas Technology Extension Program in Key Livestock Areas was implemented in 1996 in cooperation with the Department of Energy and the Department of Agriculture wherein

CvSU was designated as the National Biogas Demo and Training Center. Since then, a number of local, regional and national fora, seminars, hands-on trainings and workshops were conducted to promote the technology. Participants were from various sectors of the society: private individuals, companies, NGO s, agro-industry,

government agencies and DOE including the 20 ARECs in the country. In the course of promoting the technology, the following

were developed: training module, technoguide, a number of brochures and printed materials. The printed materials aimed to create awareness among the biogas enthusiasts. Linkages were established between DOE (represented by CvSU – AREC IV) and various government agencies suc h as the Department of Agriculture

(DA), Department of Environment and Natural Resources (DENR), Laguna Lake Development Authority (LLDA), Department of Science and Technology (DOST), and Provincial Government of Batangas to name a few. Likewise, the technical expertise of the Center was so ught

by several non-government organizations (NGOs) such as Sorosoro Ibaba Development Cooperative, Inc. (SIDCI) in Batangas Biogas Technology in the Philippines

8

City; Women’s Ecology Center of St. Scholastica ’s College at Mendez, Cavite during the time when Sis. Maryjohn Manansan was the Directress; Center for Ecozoic Living and Learning (CELL) of the Columban Fathers at Silang, Cavite; Angels ’ Hills Retreat Center at Tagaytay City and others. Hands-on trainings were conducted in Davao City, Cagayan

de Oro City, Butuan City and Gingoog City catering mainly to the participants from Mindanao. Participants from the Visayas were trained in Cebu City, Bilar, Bohol and Dumaguete City, while that from Luzon were accommodated at CvSU Mai n Campus at Indang, Cavite. The participants were asked to propagate and practice the new learned technology in their respective areas of coverage.

To date, a number of CvSU Biogas Digester Model in varying sizes had been constructed nationwide, addressing the requirements of small-medium-large livestock producers, thus, helping the government in its effort to protect the environment and energy conservation. CvSU-AREC believes that it has done its share in promoting

sustainable livestock industry development of the country and contributing to environmental protection. The Center has earned recognition for its expert services in Biogas System as applied to Power Generation and Livestock Waste Management. BAI Experience in the Promotion of Biogas Technology In 1995, the low-cost Biogas Technology using Polyethylene

tube was introduced in the Philippines by the Bureau of Animal Industry (BAI). Modification of the plastic tube biogas digester being introduced in Vietnam by Thomas R. Preston was done and applied by the research staff of BAI. With the advent of small and

affordable unit (3 to 5 cu.m. at P6,500.00-13,000.00), BAI Tubular Polyethylene Digester (BAI-TPED) has gained popularity. The main breakthrough is the utilization of polyethylene plastic

tube for the digester that is simple and easy to maintain. 9


In the same year, a program on the promotion of this low-cost biogas technology was launched to cater to the demands

of the increasing number of small household pig raisers in the country. The project was conceived so that affordable, easy to install and adaptable biogas model will be available to small household pig production units. The promotional strategy was continued by the different regional offices and local government units under the Department of Agriculture. Some livestock cooperatives and NGOs were also tapped for the project and promoted biogas technology to their members. The technology gained wider acceptance and continued to progress. There were about 254 units installed nationwide but some of these are not functioning already due to some problems i.e. damages caused by animals, natural calamities, falling trees, flood etc. Monitoring the units installed at different places became

a problem due to lack of funds for travels of staff. The biogas project gained small support from the Food and Agriculture Organizations. The farmers raising 10 to 20 pigs & feeding sugarcane juice were tapped for the project “Diversification of Sugarcane Juice. ” The project included the installation of biogas digester to selected cooperators to manage the manure. The units installed served as demonstration or show window for other pig raisers in the locality. Through this project, other interested local government officials requested the BAI to conduct training for farmers and technicians in their respective localities. The project was coordinated with other regional offices where training was conducted. The project has trained 300 farmers, 25 key farmers and 200 agricultural technicians. Repair and maintenance of the digester became the major constraints due to the unavailability of materials and technicians to do the repair of the biogas system.


10

PhilBIO and Biogas Technology Philippine Bio-Sciences Co., I nc. or PhilBIO was established

in 1998 with the goal of promoting biogas technology utilization in the country. A subsidiary of AsiaBioGas Co. Ltd, with headquarter in Thailand, PhilBIO ’s first waste-to-energy project was constructed at the Rocky Farm in the province of Rizal. To date, it has completed 60 Covered In-Ground Anaerobic Reactor (CIGAR) Projects. These systems treat wastewater effectively through proper cultivation of microbial sludge to remove significantly BOD and COD in wastewater, and capturing biogas for an on-site power use.

Status of Biogas Technology in the Philippines In 2006-2008, CvSU-AREC conducted a research entitled “ Validation of Biogas Technology and Its Utilization in the Philippines” which was funded by the Philippine Council for Industy

and Energy Research and Development (PCIERD). Result of the study showed that there are more than 900 units of biogas digesters installed throughout the country. The total capacity of these digesters is estimated at 662,457 cu.m. (Figure 2). Through the years, the country has also developed pool of experts on the technology. Appendix C shows the list of experts/

contractors/suppliers of the technology in the country. R efe re n ce s:

Avilla , HF. et.a l. 200 6. Bio ga s Te chn ology Develo pm en t in the Philipp ines: Status an d Pro pe cts. C ou ntr y Pa pe r p rese nte d to the ASEA N Rur al En ergy Fo ru m an d Technology Exhibition. Dilid ili, J.Q. e t.al. 20 08. Te rm ina l Repo rt o n Vali d atio n o d Bio ga s Techn ology an d Its Utilization in the Philippines. CvSU-AREC IV. Ma ra mb a, F elix D. 19 78. Bio ga s a nd Waste Recycling . The Philipp ine Exp er ien ce. Re ga l Pri nti ng Comp an y. www.agribusinessweek.com/philbio-the-leader-in-biogas-technologies www.pcierd.dost.gov.ph/index2.php?option=com_docman&task=doc_view&grid= 21&Itemid... 11


Figure 2. Biogas installations in the Philippines Biogas Technology in the Philippines

12

Trends and Advancements of Biogas Technology World s First Biogas-fueled Train ’

Figure 3. 60-seater biogas-fueled train A remarkable advancement in biogas technology is the world’s first biogas-fueled train in Sweden. This train makes daily trip between Linkoping just south of Stockholm, and Vastervik, 80 kilometers away from the Baltic coast. It can accommodate 60 passengers in a single car and could run 600 kilometers at a maximum speed of 130 kilometers an hour. Svensk

Biogas, which developed the train for a cost of 10 million kronor (the equivalent of €1.05 million or US $1.26 million), replaced the diesel engines of an old Fiat locomotive by two Volvo gas engines. Replacing the engine has made the train more enviro nment

friendly, since the combustion of biogas, like other biofuels, helps reduce greenhouse gas emissions. Source: AFP, October 24, 2005; Tim Fra nks, BBC New s, October 24, 2005

13


Figure 4. Synergy Biopower Containerized Control Center In August 2007, the Ontario Power Authority (OPA) has granted its first SOC (Standard Offer Contract) for a Biogas Anaerobic Digester system to Fepro Farms (Klaesi Farm) located near Cobden, Ontario. Biogas created by the Klaesi anaerobic digester is converted into electricity and heat by the Synergy Biopower System. Designed and manufactured in Canada by Powerbase, the Synergy Sy stem is a containerized, turnkey, state-

of-the-art heat and power system for biofuel applications. Source: http://www.powerbase.com/biopower/news.html


14

Figure 5. XC-Series external combustion systems 25kWe-52kWe Source: http://www.tezmanholding.com/cmpny_energy.htm#xc

Figure 6. Record-beating A4, with a maximum speed of 327.2 km/h (203 mph), runs on biogas Source: http://www.autobloggreen.com/tag/biogas/

15


Figure 7. Guascor 957 kW engine generator set Source: http://www.ecw.org/prod/2008BiogasCaseStudy.pdf

Figure 8. Biogas purification using pressure swing absorption process Source: http://www.moleculargate.com/landfill-gas-purification.html


16

Chapter II

BIOGAS TECHNOLOGICAL PROCESS What is Biogas? Biogas is a combustible gas that all organic matters (e.g. animal manures and crop residues) produce when fermented and decomposed by anaerobic bacteria under conditions of uniform humidity, constant temperature and full enclosure in a tank. Biogas is very c ommon in nature and can easily be detected

in the marshland, rice fields and domestic sewage canal. If you put bamboo stick into the black mud at the bottom of a pond, bubbles can be observed to come out. These bubbles are biogas.

This gas is produced by different kinds of bacteria under certain condition. These bacteria eat organic substances and biogas is a kind of excretion from them. The bacteria work well in the absence of air in the environment, so that full enclosure is necessary to enhance biogas production. Biogas is composed of 60 to 70 percent methane (CH 4), 30

to 40 percent carbon dioxide (CO 2) and traces of other compounds

such as hydrogen sulfide (H2S), nitrogen gas (N2), hydrogen gas (H 2), carbon monoxide (CO) and other hydrocarbon compounds. It is about 20 percent lighter than air and has ignition temperature in the range of 650 oC to 750 oC. Methane itself is odorless, colorless

and tasteless, but the other gases contained in biogas give it a slight smell of rotten egg. The gas burns with clear blue flame similar to that of LPG. Upon complete combustion, one cubic meter of methane can reach a temperature of 1400oC and release 8,562 to 9,500 kcal heat (1kcal of heat will raise the temperature of 1 kg of water by 1 oC).


18

One complete combustion of one cubic meter of biogas can release

5,500 to 6,500 kcal of heat.

Biogas Technological Process The biogas technological proces s (Figure 9) is accomplished

by means of fermentation/digestion of organic materials (such as crop residues, human and animal wastes, distillery wastes) through the actions of a number of microorganisms under anaerobic condition to produce biogas and sludge. Anaerobic condition is provided by a simple device known as “ biogas digester” (further discussion in Chapter IV).

Figure 9. The biogas technological process

Stages of Biogas Fermentation There are three important stages in biogas fermentation process: (1) liquefaction stage; (2) acid production stage; and (3) methane production stage (Figures 10 and 11). 19


Figure 10. Stages of biogas fermentation

Figure 11. The three stages of fermentation


20

I n the first stage,

liquefaction stage, a group of facultative bacteria (fermenting bacteria) acts upon the organic substrate. By enzymatic hydrolysis, the polymers are converted into soluble monomers that become the substrate for the next stage. In the second stage, acid-production stage, the soluble substrate from the first stage is acted upon by ac etogenic bacteria

to yield hydrogen, acetic acid and others such as propanic, butyric, lactic and formic acids. These become the substrate for the last stage. Studies showed that 70% of the methane produced come from acetic acid, thus, making it the single most important substrate for methane production. In the third stage, methane production stage, the methane producing (methanogenic) bacteria utilize as substrate the simple

compounds such as acetic acid, hydrogen, formic acid and CO 2 to form methane and carbon dioxide.

Classification of Biogas Fermentation Process There are many processes which could be adopted for the fermentation of different wastes for various purposes. They can be divided according to the following: 1. Method of feeding a. Continuous Feeding

The manure is fed continuously into the digester everyday. The digester collection system/mixing tank is directly connected to the wastes canal sy stem of the livestock

project. The effluent is discharged simultaneously in the same amount of the influent. Thus, the fermentation in the digester goes on continuously. This process is characterized

by constant fermentation, uniform gas production and easy

21


control. This method is widely used in medium and large size digesters. b. Semi-Continuous Feeding

A large quantity of feedstock is put into the digester in the first feeding. When gas yield gradually drops down, fresh

raw material is introduced and the same amount of effluent is being discharged regularly. c. Batch Feeding

Digester is charged with feedstock manually by batch. When gas yield drops down to a low level after a period of fermentation, the digester can be emptied and fed once again. 2. Temperature a. Thermophilic Process

Thermophilic fermentation can be accomplished with a temperature ranging from 45-60 degrees centigrade. This is characterized by rapid fermentation, high gas yield (2 ºC gas/m3 digester/day) and short retention time. This system

is appropriate in fermenting wastes from distilleries, wine and sugar refineries where high temperature feedstock is available.

b. Mesophilic Process

The temperature of mesophilic fermentation ranges from 30oC to 45oC. This process feature low gas production (1 m3 biogas/m3 digester/day), simple operation, low initial cost, and is suitable for low temperature industrial wastewater treatment.


22

c. Ambient Temperature Process

The operating temperature for this process ranges from 18 C to 30oC. The fermentation of this process is much influenced by earth and atmospheric temperature. Its main features include: suitable for rural areas, low cost, gas production is dependent on temperature (0.25 to 0.5 m 3 gas/m3 digester/day), and simple construction. Below 10 oC, bacterial activity ceases, thus, gas production stops. o

3. Fermentation Stages a. Single-Stage Fermentation

The three stages of biogas fermentation take place in the digester tank, e.g. fixed-dome digester and the other type comprising of one tank. In this case, the solid retention time (SRT) and hydraulic retention time (HRT) are the same (SRT=HRT). b. Two-Stage and Multi-Stage Fermentation

These processes indicate that fermentation occurs in two or more digesters. Feedstock is first charged in the first tank and the effluent coming from the first digester is further digested in the second digester. Multi-stage digesters

are characterized by long retention time, good decomposition of organic matter and high investment.

Factors that Influence Biogas Production There are several factors which affect or stimulate gas production. The operational success of the digesters depends on the following parameters:

23


1 . Temperature

The temperature directly affects process conditions by microbial growth rates. The methane bacteria are very sensitive to sudden temperature changes, and for optimum process and stability, the temperature should be controlled carefully within a narrow range of selected operating temperature. It should be remembered that higher temperature yields more gas. 2. Retention Time (RT)

Retention time is the theoretical time that the input material remains inside the digester before it is expelled. Temperature is inversely related to retention time; the higher

the temperature, the shorter is the retention time. The volume of slurry input should be given sufficient time for the bacteria to digest the materials before it leaves the digester. Theoretically,

Digester slurry volume RT (Days) = Daily input volume

or, Digester slurry volume = RT X Daily input volume Table 1. Preferable retention time and gas production at different temperatures Temperature

10 15 20 25 30 35

˚

˚

˚

˚

˚

˚

C C C C C C

Selected Retention Time (Day) 70 45 35 30 20

Gas Production Cow P ig C hicken (lit/head/day) 330 600 700 630 1000

100 190 220 260 310

4 6 9 11 13


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3. pH or degree of Acidity or Alkalinity

The optimum pH value for biogas fermentation is 6.5 – 7.5 although it may tolerate a pH level of 6 to 8. The pH value varies and adjusts automatically. Below 6 or above 8 necessitates adjustment of pH level for it may inhibit or stop the digestion process. Methane producing bacteria are very sensitive to pH condition and changes. Under acidic co nditions,

pH values can be improved by adding ash fertilizer, diluted ammonia water or mixture of them, fermented liquor and lime.

4. Carbon-Nitrogen (C/N) Ratio The bacteria need both carbon and nitrogen to survive.

They consume carbon about 25 to 35 times faster than they consume nitrogen. Thus, proper digestion proceeds at an optimum rate when the carbon content of the slurry or input materials used is about 20 to 30:1. High C/N ratio means short supply of nitrogen and fermentation is subjected to acidic inhibition. Low C/N ratio means excessive ammonia which lead to inhibition. The common sources of carbon are leaves, grasses and raw materials rich in cellulose. Sources of nitrogen are manure and urine. C/N ratio of some organic materials are shown below. Table 2. C/N Ratio of some organic materials M a terial C attle m a nure (with stra w) D a iry m anu re H o rse P ig m anu re P oultry m anu re (fre sh) R ic e straw S aw d ust S ugar c an e (trash) W ate r h y ac inth Source: PAES 414-2:2002.

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C /N R a tio 2 5-3 0 1 0-1 8 19 5-8 6 -10 48 -11 5 30 0-7 23 50 2 0-3 0

Materials with high C/N ratio could be mixed with those of low C/N ratio to bring the average ratio of the composite input to a desirable level.

5. Agitation

Without stirring the small digester, the fermenting slurry can be divided into three layers: scum in the upper part, liquid in the middle, and sludge at the bottom. The main function of stirring is to break these layers and distribute

the slurry inside the digester uniformly. The procedure promotes contact between the old and fresh slurry and between microbes and substrate , thus, accelerating fermentation rate and enhancing gas yield. There are three kinds of stirrer: a. Mechanical stirrer

Mechanical stirrer (Figure 12a) can be operated manually or by means of electricity. The usual construction is a pipe having baffle placed at the middle of the digester to provide

the stirring action. b. Liquid Stirrer

In this method, a certain amount of the effluent is drawn from the outlet of the digester by means of pump or other manual device and returned into the inlet to provide a strong liquid stir (Figure 12b). c. Gas Stirrer

The biogas is drawn from the digester by means of a pump and returned back to the bottom of the digester to promote stirring action (Figure 12c). Biogas Technology in the Philippines

26

Figure 12a. Mechanical stirrer

Figure 12b. Hydraulic stirrer

27


Figure 12c. Gas stirrer 6. Types of raw material

The kind of raw material as input is one of the major factors which influence gas production. The common materials used for methane production are crop residues, human excreta, animal wastes, distilleries and food processing plant wastes, and others which contain high concentration of organic waste. The potential gas yield of some raw materials is presented in Table 3. 7.

Fermentation process

The kind of fermentation process being used has a great influence on gas production. The most common types are single-phase and two-phase fermentation processes. Other types are: Anaerobic Filter (AF); Up flow Anaerobic Sludge Bed (UASB); Expanding Bed; Biological Cycle (AF & UASB). Biogas Technology in the Philippines

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Table 3. Potential gas yield of selected raw materials (Concentration: 6%) Materials Cow dung Horse dung Pig dung Chicken dung Human excreta Rice straw W heat straw Corn stalk Green grass

Liters of Biogas per kg T otal Solids 110-300 240-340 220-480 310-350 330-470 320-470 370-510 360-550 400

8. Toxicity

Mineral ions, heavy metals and detergents are some of the toxic materials that inhibit the normal growth of pathogens in the digester. Small quantity of mineral ions (e.g. sodium, potassium, calcium, magnesium, ammonium and sulphur) also stimulates the growth of bacteria, while very heavy concentration of these ions will have toxic effect. Similarly, heavy metals such as copper, nickel, chromium, zinc, lead, etc., in small quantities are essen tial for the growth

of bacteria but their higher concentration has toxic effects. Likewise detergents including soap, antibiotics, organic solvents, etc. inhibit the activities of methane producing bacteria and addition of these substances in the digester should be avoided. Although, there is a long list of the substances that produce toxicity on bacterial growth, the inhibiting levels of some of the major ones are given in Table 4.

29


Table 4. Toxic level of various inhibitors Inhibitors Sulphate (SO4) Sodium Chloride (NaCl) Nitrate Copper (Cu++) Chromium (Cr+++) Nickel (Ni+++) Sodium (Na+) Potassium (K+) Calcium (Ca++) Magnesium (Mg++ ) Manganese (Mn++)

Inhibiting Co ncentration 5,000 ppm 40,000 ppm 0.05 mg/m l 100 mg/l 200 mg/l 200-500 mg/l 3,500 - 5,500 mg/l 2,500 - 4,500 mg/l 2,500 - 4,500 mg/l 1,000 - 1,500 mg/l above 1,500 mg/l

Source: The Biogas Technology in China, BRTC, China, 1989.

R ef er en ce s:

Sangalang, et.al.. 1993. Co mprehensive Utilization of Bioga s Technology. Proceed ings of the First National Training Co urse on Biogas Technology. CvSU-ANEC. ___ ___ _. 19 96. Bio ga s Techn ology: A Tra ini ng Ma nu al f or Exten sio n. FAO/TC P/ NEP/4451-T ___ ___ _. Bio ga s D ige st. Volume I. Bio ga s B as ics. ISAT. ___ ___ _. 19 89. Th e Bi og as Tech no lo gy in C hin a, BRT C, Chin a..


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Chapter III

COMPREHENSIVE UTILIZATION OF BIOGAS TECHNOLOGY Biogas system requires a simple plant known as biogas digester, and users have only to feed proper amount of waste materials everyday, every two or every three days. This continuous operation can give users a constant gas volume which

can supply the daily fuel requirement of a family or a business. Effluent from this plant could be stored in a storage tank and could be used as liquid fertilizer. Sludge at the bottom of the plant is also pumped out and used as organic fertilizer in the farm. A biogas plant therefore produces two resources, the gas and the effluent. It also treats waste materials and in the process produces biogas. The plant itself therefore, serves as anti-pollution device (Figure 13).

Biogas Utilization Biogas burners or stoves. Biogas burners or stoves

(Figure 14a) work satisfactorily for domestic cooking under water pressure of 75 to 85 mm. The stoves may be single or double burner varying in capacity from 0.22 to 1.10 m3 of gas consumption per hour. Generally, stoves of 0.22 and 0.44 m3 (8 and 16 cu ft)

capacity are more popular. A 1.10 m3 (40 cu ft) burner is recommended for a bigger family with larger plant size. Biogas lamp. Biogas can be used for lighting (Figure 14b) in non-electrified rural areas. Special types of gauze mantle lamps

consuming around 0.07 to 0.14 m 3 of gas per hour are used for household lighting. A great variety of lamps which have single or

double mantles are already available in the market. Generally, mantle lamp is used for indoor purposes and 2-mantle lamps for outdoors. Biogas Technology in the Philippines

32

Such lamps emit clear and bright light equivalent to 40 to 100 ft candle powers. These are generally strong, well built, bright, efficient and easy to adjust. Compared to stoves, lamps are more difficult to operate and maintain.

Figure 14a. Biogas stoves/burners.

Figure 14b. Biogas lamp

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Fuel for Engines. Biogas can be used to operate four stroke

spark ignition engines. Biogas engines are generally suitable for powering vehicles like tractors and light duty trucks as has been successfully experimented in China. When biogas is used to fuel such engines, it may be necessary to reduce the hydrogen sulphide content. Using biogas to fuel vehicles is not much of an attractive

proposition as it will require carrying huge gas tanks on the vehicle.

Electricity Generation. Generating electricity (Figure 14c) is a

much more efficient use of biogas than using it for gas light. From energy utilization point of view, it is more economical to use biogas to generate electricity for lighting. In this process, the gas consumption is about 0.75 m 3 per kw hour with which 25x40-watt lamps can be lighted for one hour, whereas the same volume of biogas can serve only seven lamps for one hour (BRTC, 1983).

Figure 14c. General Motors dual-fuel generator sets designed by Don Hardy with power output of 60 to 200 kW Source: http://home.philbio.com.ph/docs/On_Going_Projects/Beijing%20RE%20conference


34

Refrigerating machines. Biogas can be used for absorption type

refrigerating machines (Figure 14d) operating on ammonia and water and equipped with automatic thermo-siphon. Since biogas is only the refrigerator’s external source of heat, just the burner

itself has to be modified. Refrigerators that run with kerosene flame could be adapted to run on biogas.

Figure 14d. Double-door refrigerating machine Source: www.RefrigeratingMachines.com

What Can You Do with One Cubic Meter of Biogas ?

Table 5 shows some typical applications of one cu.m. of biogas.

35


Table 5. Applications of one cu.m. biogas 1 m

Application L ig h tin g

b i o g as eq u i va le n t

e q u a l to 6 0 -1 0 0 w a tt b u lb f o r 6 h o u rs

C o o k in g

c a n c o o k 3 m e a ls f o r a f a m ily o f 5 -6 0.454 kg of lpg 3.47 kg of firewood 1.40 kg of charcoal

F u e l re p la c e m e n t

0 .7 k g o f p e tro l 0.52 kg of diesel 0.24 m

3

of propane

S haft power

c a n ru n a o n e h o rse p o w e r m o to r f o r 2 hours

E le ctric ity g en era tio n

c an g en era te 1 .2 5 k ilo wa tt h ou rs o f electricity

Sludge Utilization Sludge can be utilized in the following ways: as fertilizer (liquid and solid form) to agricultural crops, as dipping media for seed soaking, as feeds for freshwater fish, as feed supplement for pigs (Appendix A) and as soil conditioner, among others. Table 6 shows the mineral composition of sludge. Table 6. Mineral composition of sludge Mineral N, total, % P2O5, total, %

Solid Sludge 2.07 7.31

Liquid Sludge 0.08 0.15

P2O5, available, %

4.97

0.15

K2O, total, %

0.75 4.9 0.64 0.77 0.01 145 0.96 49.6

0.03 trace 0.66 0.18 0.28 0.47 -

Ca, % Mg, % Fe, ppm Cu, ppm Zn, ppm Mn, ppm Organic matter, %

Source: Maramba, 1978.


36

Figure 15a. Sludge used as organic fertilizer

Figure 15b. Liquid sludge is recycled to clean animal pen.

37


Biogas Technology as Waste-Treatment Facility

Figure 16. Biogas technology in wastewater treatment system Biogas Technology in the Philippines

38

Chapter IV

DESIGN OF BIOGAS DIGESTER The biogas digester is a physical structure commonly known

as biogas plant. It is also known as bio-digester, bio-reactor or anaerobic reactor. The main function of this structure is to provide anaerobic condition for the bacteria to survive. As a chamber, it should be air and water tight. It can be made of various construction materials and in different shapes and sizes. Some of the commonly used designs are discussed below.

Design of Biogas Digester According to Forms and Structure The biogas digester design can be grouped according to their varied forms and structures. 1 . According to Gas Storage

The design of biogas digester may vary accordingly to suit the requirements of the owner. This can be divided into three groups, namely: fixed-digester, floating gas holder and bag digester. a. Fixed-Dome Digester

Fixed-dome digester (Figure 17a) is the most common type of design. The four major components of the digester which are gas storage, fermentation chambers, hydraulic tank and inlet tanks are integrated into one structure. Its distinct advantages over the other designs are: 1. All concrete construction, hence, durable and life long investment. Simple structure. Least cost. 2. No moving parts and metal components, thus, easy to maintain. Biogas Technology in the Philippines

40

3. Capable of generating higher gas pressure (on the average 10 times higher than floating gas holder type). 4. Can be completely constructed underground, thus save land space. Input materials flow easily into the digester by gravity, hence simplifying operation.

Figure 17a. Fixed-dome digester b. Floating Gas Holder Digester

The floating gas holder digester makes use of a floating tank for gas storage. This can be further subdivided into: 1.

Top Floating Gas Holder Digester The floating tank for gas storage is directly installed

on top of the digester. This is usually employed for small size digester (Figure 17b 1).

Figure 17b1. Top floating gas holder digester 41


2. Separate Floating Gas Holder Digester

The application of this style is for medium to large size digester. There are two tanks involved: one is the fermentation tank and the other is the gas storage tank (Figure 17b2).

Figure 17b2. Separate floating gas holder digester c. Bag Digester The bag digester is a type of digester with a bag for gas storage (Fig. 17c).

Figure 17c. Bag digester Biogas Technology in the Philippines

42

2. According to Geometrical Shapes

Biogas digester can be constructed in various geometrical shapes: vertical cylinder, spherical, rectangular, square, pipeshaped, oval, spindle-shaped, elliptical, arch, oblate, etc. (Figure18).

Figure 18. Construction shapes of biogas digester

43


3. According to Orientations

The arrangement of the different components of biogas system can vary according to what is suitable to the condition of the area. The different orientations of inlet and outlet are shown in Figure 18 for design flexibility.

Figure 19. Different orientations of inlet and outlet for design flexibility


44

4. According to Buried Position (Figures 20 to 22)

Biogas digesters can be erected either of the following ways: a. Ground digester

Figure 20. Ground digester b. Semi-buried digester

Figure 21. Semi-buried digester

45


c. Underground digester

Figure 22. Underground digester Advantage s and Disadvantages of Various Designs 1. Cylindrical Fixed-Dome Digester Advantages:

Reinforced concrete construction · No steel sheets required · Generally, it runs on batch-continuous process, i.e. plant waste maybe included · The total cost is normally less than that of floating ·

gasholder

Plant materials maybe used · The digester and the gasholder maybe built below ground level, hence, it is easy to insulate them in cold regions · If built underground, the above surface area maybe used for other purposes. ·


46

MOVABLE COVER

GAS PIPE

GAS STORAGE

OUTLET PIT

INLET PIT

INLET PIPE OUTLET PIPE

FERMENTATION CHAMBER

Figure 23. Cylindrical fixed-dome digester Disdavantages:

No provision for stirring the slurry in the plant · Stirrer can be fitted through dome · The necessity of removing the sludge twice or more often in a year · Outside China, this type is not very popular in view of lack of construction and plastering experience · Requires highly skilled workers for construction ·

2. Spherical Hydraulic Digester Advantages: ·

The same features as cylindrical fixed-dome digester

Disdavantage: ·

47

More difficult to construct than the cylindrical fixeddome


MOVABLE COVER

GAS PIPE

HYDRAULIC CHAMBER

INLET PIT INLET PIPE

FERMENTATION CHAMBER

Figure 24. Spherical hydraulic digester 3. Ellipsoidal Hydraulic Digester Advantages and Disadvantes are the same with Spherical Digester. MOVABLE GAS PIPE

HYDRAULIC CHAMBER

INLET PIT

INLET PIPE FERMENTATION CHAMBER

Figure 25. Ellipsoidal hydraulic digester Biogas Technology in the Philippines

48

4. Flexible Bag-Type Combined Digester/Gas Holder Advantages:

Portable · Constant gas pressure may be obtained · Relatively quick to erect · Low capital cost ·

Disadvantages: ·

Must be made of strong plastic resistant to ultra violet rays (Hypalon-Neoprene plastic is used)

·

Cost depends on local price of plastic materials (if available)

·

Plastic can be accidentally cut during handling and installation

·

· · ·

Should be provided with pressure release valve, otherwise, the bag may explode Rodents have been known to destroy the plastic bag Stirring is not possible Bends in inlet and outlet may cause blockage

GAS PIPE

GAS

LEVELLED SURFACE

SLURRY

INLET

OUTLET

Figure 26. Flexible bag-type combined digester/holder 49


5. Two Chamber Rectangular Digester with Floating Gas Holder (without water seal and with water seal) Advantag Adv antages: es:

Digester is easy to construct · Uniform gas pressure · Offers the possibility of heating the slurry by using solar energy ·

Disadvantages:

. High initial cost · Needs frequent stirring · Clogging problem have been experienced · Susceptible to scum formation · Needs the services of a skilled welder · Gas tank is easily corroded · Leakage is a perennial problem · High rehabilitation cost • Needs annual maintenance

MIXING MIXING DEVICE

GAS VALVE

MIXING MIXING DEVICE COVERED MANHOLE

FLEXIBLE HOSE

INLET GAS PIPE

OUTLET OUTLET

GAS

INLET

HOLD ER G U ID E

(without water seal)

(with water seal)

Figure 27. Two-chamber rectangular digester with floating gas holder


50

6. Fixed-Dome Digester with Separate Gas Holder Advantag Adv antages: es: · · ·

The digester dome is subjected to little gas pressure (determined) by the weight of the gas holder Uniform gas pressure; hence, appliances may be designed and used at their optimum working conditions No steel sheets or reinforcing steel bars are needed for the gas holders

Disadvantage: ·

Additional work and cost of building the water tank as gas holder

GAS PIPE REMOVABLE MANHOLE

BAMBOO CEMENT

INLET

GAS HOLDER

FLOATER

COVER SEALED W/

LOOSE

CLAY

COVER

GAS

WATER

SLURRY

DISPLACEMENT TANK

Figure 28. Fixed-dome digester with separate gas holder 7. Deenbandhu Biogas Digester Advantages: · All

concrete construction hence, durable · Operates on displacement principle as in Chinese digester 51


Low initial cost · Uses commonly available construction materials ·

Disadvantages: · ·

Needs special skills and training for construction Non-uniform gas pressure

MIXING

GAS OUTLET PIPE

TANK

OUTLET INITIAL SLURRY LEVEL

TANK

PVC PIPE DIGESTER

TANK

OPENING

CENTER

Figure 29. Deenbandhu biogas digester 8. Rectangular/Square Fixed Dome Digester Advantag Adv antages: es:

Easy to construct · Uses commonly available construction materials · Operates on displacement principle · Less susceptible to scum formation · Less foreign matters accumulation inside the digester · Can be constructed above/under ground · Can be easily adapted for floating gas holder digester ·


52

Disadvantages: ·

·

Non-uniform gas pressure Requires special training for construction

GAS PIPE

SLURR Y TANK TANK TO DECREASE PRESSURE PRESS URE ON

GAS HOLDER TOP

GAS OUTLET

INLET

SLURRY

Figure 30. Rectangular/Square fixed-dome digester

53


Digester Models in the Philippines There are several models of biogas digester already in the

country. Most common are fixed-dome type, bag type, and for larger applications, the covered lagoon digester. There are also some floating-type biogas digesters, while the drum-type is very few. Depending on the size of the livestock project, the authors are recommending the following digester models/designs for small,

medium and large applications: DSAC-Model Biogas Digester, Tubular Polyethylene-Based Digester (TPED) and Covered Lagoon Digester, respectiv ely.

DSAC-Model biogas digester is a rectangular fixed-dome digester which is a combination of Chinese and Indian model. This model is durable because of its all-concrete construction and is adaptable to small-medium-large scale applications (see details in Chapter V). The TPED model is an improved bag-type digester adaptable to small scale application. This modified technology is

easier to build and less expensive (see details in Chapter VI). However, this model is mainly used for energy-generation and not for waste treatment. The covered lagoon digesters are huge digesters adaptable to large scale applications. The system is generally used in power

generation (see details in Chapter VII).


54

Chapter V

DSAC-MODEL BIOGAS DIGESTER The DSAC-Model biogas digester is a rectangular fixeddome digester. It is a modification combining the features of Chinese and Indian models.

n

Among its special features are the following: Environment-friendly, 60%-80% pollution reduction capability Low cost Easy to construct and simple to operate All concrete construction, durable and with less maintenance Flexibility of design Self stirring With built-in safety mechanism Can generate biogas from 35-60% of the digester volume

n

Adoptable to small-medium-large scale animal production,

n n n n

n

n n

slaughterhouses and food processing plant

Figure 31. DSAC-Model biogas digester (Utility Model No. 2-1997-15098) Biogas Technology in the Philippines

56

Components of DSAC-Model Biogas Digester The biogas digester is composed of an inlet, inlet pipe, gas storage, digester and the outlet chamber (Figure 32).

Figure 32. Basic components of a DSAC-Model biogas system The Inlet. The inlet serves as the collection tank of the

manure. It can either be circular or rectangular in shape. It is divided into two compartments, namely: the collection compartment and the inlet compartment. The collec tion compartment is directly connected to the canal system of the animal pen. It collects the manure and serves as a sedimentation

tank where foreign matters which are non-biodegradable like sand, hair, etc. could be collected to avoid its entry to the d igester.

The inlet compartment is connected to the digester through an inlet pipe which then conveys the slurry to the digester. The inlet

should be provided with cover to avoid the entrance of rainwater and for safety purposes. The Digester and Gas Storage. This is the fermentation tank which provide anaerobic condition needed for the bacteria to act on the organic wastes. The fermentation process is allowed

57


to be completed in the digester for a certain period of time known as the retention period. During the fermentation process,

biogas is generated and stored in the gas storage which form as the dome cover of the digester. The structure must be air- and water-tight. The Outlet Chamber. The outlet chamber serves as the hydraulic tank which maintain the pressure of the biogas inside the gas storage. It can either be circular or rectangular in shape. The chamber is provided with discharge outlet where sludge or effluent can be collected. Manhole . Between the digester and the outlet chamber is a manhole which provide an access to the inside of the digester if necessary. The Gas Line. The gas line is the delivery line of gas

from gas storage tank to the appliances being used. It is located at the midline of the dome cover. It is made of stainless steel pipe.

Principles of Operation The biogas plant operates in a displacement principle. The slurry in the inlet flows into the fermentation tank (digester)

through the inlet pipe. Fermentation process occurs inside the digester due to the action of bacteria. During the fermentation process, biogas is generated and stored in the gas holder. The slurry is allowed to stay inside the digester for a certain number of days to allow the fermentation process to complete. Once digested, the slurry settles down as it becomes more dense compared to the fresh slurry. The digested slurry is then pushed by the incoming fresh slurry into the outlet chamber. The pressure developed by the gas generated inside the digester assists also in pushing the digested slurry towards the outlet chamber to the discharge outlet.


58

Design Formulas Consider a rectangular fixed-dome biogas digester, the design formulas are as follows (see Figure 33).

f

W h

W

f

h

V1

V2

L

Figure 33. Design formulas 59


Let

h = height of rectangle w = width of digester f = top of dome R = hydraulic radius V1 = gas chamber volume V2 = slurry chamber volume Vt = total volume of digester Vo = volume of outlet Vs = volume of slurry

The useful relationship for this type of digester are: 1. f/w = 1/3 W2 + 4f2 2. R = 8f 3. Vo = 1/3 x V2, that is, Vo is one third the slurry chamber volume 4. Vs = V2, that is, the slurry volume is equal to the volume of digester below the top dome. 5. Height of inlet/outlet pipes = 1/2 h, that is, the inlet/ outlet pipes are placed 1/2 the height of the wall. 6. Mixing pit volume should be slightly larger than the daily charge. 7. Manhole dimension is standard for all volumes of digester.


60

Sizing of Biogas Digester There are two approaches in determining the size of a biogas digester. digester. The decision is made by the owner/operator owner/operator to fit his needs. 1. The size of the unit unit to to produce a certain amount of gas needed 2. The size of the unit to process/treat a given amount of organic matter (pig manure, chicken manure, etc.) as a waste management system. Generally, in case wherein the volume of organic matter to be treated is known and the need for gas is minimal, the overriding consideration, therefore is the quantity of the raw materials to be treated. treated. Other questions questions are: What What digester volu volume me is need needed ed to hand handle le thes these e mate ria ls ? Wha t is the quantity of gas expected? How will this gas be utilized? What is the cost involved? For example: Assume a medium-sized piggery with one (1) boar, fifteen (15) sow and one hundred twenty fatteners. The average daily manure production are: 1 Boar = 4.91 kg 15 Sow = 3.97 kg 120 Fattener = 3.84 kg Manure Production Production = 1 boar * 4.91 kg + 15 sows * 3.97 kg +120 fatteners * 3.97 kg = 4.91 + 59.55 + 460.8 = 525.26 li/day Slurry Volume = 525.26 liters * 2 (1 vol. of manure: 1 vol. of water) = 1,050.52 li/day

61


Digester Volume = 882 li/day *40 days retention time = 42,020.80 liters = 42.02 cu.m. Estimated Gas Production = 42.02 cu.m. * 0.5 cu.m. biogas/ cu.m. digester volume = 21.01 cu.m. biogas per day

Pre-Construction Pre-Construction Consideration Consideration Planning/Preparation

It is recommended that the builder reads the entire construction procedures to have an idea of what is involved, the time period required and the construction materials to be used.

Figure 34. Planning/Preparation


62

Some important reminders in planning for the construction

of biogas unit: 1. Order Order and and purchas purchase e all materi materials als in advanc advance. e. 2. Prepare Prepare all tools needed needed in the construction. construction. 3. Building a biogas tank is not si milar to building a house or a piggery. piggery. One crack in a house or piggery structure

is permissible permissib le but not in a biogas digester. digester. Any source of leak for gas will render the biogas digester useless.

4. Water-proofing ater-proofing concret concrete e is relatively relatively easy easy,, but gasproofing is difficult. difficult. This requires materials not applied

in ordinary masonry work. 5. Costing. Costing. Ask the questio question n whether whether some some materia materials ls could be suitably substituted s ubstituted by others which are less expensive but adequate for the job. 6. Available labor. labor. Check if the required required labor and technical skills could be easily obtained and if not, where to secure them. table. The water water table should not exceed 7. Check water table. half of the height height of digester wall. wall. If necessary, necessary, the whole structure may be elevated to compensate for the high water table (although it may involve some problems like more backfill needed and more efforts in lifting/handling manure into the the digester). As a rule, it is best to avoid high groundwater areas for biogas units. construction during rainy season for it may cause 8. Avoid construction construction delay, thus, affecting the quality of concrete work. 9. Follow strictly the scientific methods for working with concrete. The payoff is highly durable, more more lasting and efficiently functioning biogas unit.

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10. Other reminders. Consider the available animal waste, amount of manure available, amount of gas production and potential utilization of biogas byproducts.

Site Consideration The following guidelines are helpful in choosing an ideal

site for biogas project. 1. Water table. Biogas units should be constructed at a site where water table is low. The maximum that a water table may be allowed to rise is ½ of the height of the digester. If the water table in the selected site is too high, look for another site. 2. Site location. It should be located as much as

possible downhill or downstream with respect to a well or spring. Ideally, the minimum distance should be 15-20 meters to avoid water contamination in case of leaks from the digester. 3. Accessibility. The site should be as clean as possible to the point of gas utilization, but at the same time, close to the source of raw materials such as piggery or poultry. 4. Soil formation.

The biogas digester should be constructed on stable soil foundation. 5. Vegetation. The digester should be away from roots of big trees that may damage the structure. 6. Sunlight. The digester is completely underground. In the tropics, the unit should be placed in an open area for greater exposure to sunlight. The heat provided by the sun will promote greater gas production.


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7. In cold areas, the digester should be constructed underneath the house/kitchen/ animal stalls to protect it from extremely low temperature. 8. Feeding. The feeding of raw materials to the inlet/mixing tank should be accomplished via sloping canals or through the action of gravity. This is advisable for increased efficiency and less labor cost in handling the manure. 9. The site should be closed to where the effluent is to be used/stored like vegetable garden or drying bed.

Construction Techniques (DSAC-Model Rectangular- Fixed Dome Digester) a. Lay-outing

After the place has been carefully identified, the area should be cleared from grasses, debris and other materials which might obstruct the free movement of workers doing construction. Minor site development is necessary for soil surface with sloping terrain; however, this is not needed for flat surfaces.

Figure 35. Lay-outing 65


b. Excavation

Earth bank should be as vertical as permissible. A 20 cm gap on both sides shall be allowed for backfill.

Figure 36. Excavation c. Bottom Construction

For a biogas plant of not more than 10 cu.m., a 20 cm x 20 cm footing shall be provided to carry the load of the digester wall. The soil must be properly drained and compacted. The footing must be reinforced with 10 mm RSB properly spaced with stirrups. d. Flooring Construction A 10 cm thick flooring s hall be reinforced with 10 mm diameter

RSB spaced at 40 cm on center both ways. The RSB shall be connected to the footing. Use class A concrete mixture with water proofing compound.


66

Figure 37. Bottom construction

Figure 38. Flooring construction e. Wall Masonry Wall should be reinforced concrete hollow blocks. The wall

should be reinforced with 10 mm reinforcement steel bars placed at 40 cm distance (vertical bars) and every two layers for the horizontal bars. Use class A mortar with water proofing

compound. Provide column in excess of 3 m span. Tie wires for the screen must be embedded and anchored to the horizontal bars. 67


Figure 39. Wall masonry f. Construction of Inlet A 200 mm diameter concrete pipe is connected to the digester

at about half-way down the digester wall. The other end of the pipe is connected to the mixing pit where mixing of manure and water is done. The inlet pipes must be laid at a 30 degrees angle to the digester wall. g. Construction of Hydraulic Tank

This tank serves as the outlet tank. It must be provided with stairs and open manhole as access into the inside of the digester. The floor level must be on the same level with the upper part of top beam. The height of overflow must be at least 10 cm lower than the lower surface of the dome.


68

Figure 40. Construction of inlet

Figure 41. Construction of hydraulic tank

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h. Top Beam Construction

A 20 cm x 20 cm beam reinforced with 4 - 10 mm diameter RSB with stirrups spaced at 20 cm shall be connected to support the top dome. The beam shall be anchored on the vertical bars.

Figure 42. Top beam construction i. Dome Construction

The dome should be cast-in place. The curvature of the form works is based on the design curvature of the dome (inside). The curvature of the reinforcement bars shall be based on the curvature of the dome plus 1/2 the thickness of the dome which should be not less than 5 cm. The reinforcement must be 10 mm diameter RSB spaced at 15 cm (both the curved and the horizontal bars) and the curved bars shall be anchored at the top beam.


70

Figure 43a. Dome construction

Figure 43b. Dome construction 71


j. Sealing the Digester

The biogas digester must be water-tight and air tight. The walls and dome must be reinforced with screen before plastering with class A mortar mixed with sealing compound. Apply three layers of plaster (1/2 ”, 1/4 ”, and 1/4 ” of thickness). Each layer must be applied continuously and should

be finished within one day. All corners must be curvedfinished. The plaster should be mixed with water proofing compound.

Figure 44. Sealing the digester


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k. Air and Water-Tightness Tests

Figure 45. Water-tightness test a. Water -Tightness Test For Shallow Groundwater

1. Dry the digester and check the leakage appearing on the wall, dome, and bottom. If water drips on the inner surface of the digester, this means that the digester is not to water-tight. 2. If water level in the digester changes more than 5 mm for 12 hours, the digester is water-tight by the level of groundwater.

3. Lower the groundwater level and follow the method for deep groundwater. For Deep Groundwater

1. Pour water until the digester is filled with water. 2. At first, the concrete absorb some amount of water. Wait for 3-5 hours and then mark the water level. 3. If drawdown of water level is not more than 5 mm for 12 hours, the digester is water-tight enough. Cover the open area to prevent evaporation. 73


Figure 46a. Air-tightness test b. Air-Tightness Test

1. Drain water until the hydraulic pressure tank is empty. 2. Set manometer (pressure meter) and valve. 3. Close valve and pour water until pressure inside the digester becomes the desired value of 80-120 cm water. 4. If the pressure drawdown is not more than 3% of original value, the digester passes the air-tightness test. 5. The pressure inside the digester

will be affected by many factors such as temperature, atmospheric pressure, and sunlight. If there is no tendency of pressure drawdown, then the digester passed even if some fluctuation is observed. Figure 46b. Manometer


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Table 7. Bill of materials for a 6 cu.m. DSAC-Model biogas plant Quantity 300 60 30 8 2 75 4 40 6 2 2 2 2 1 1 20 1

Unit pcs. pcs. pcs. cu.m. cu.m. pcs. kgs. pcs. kgs. pcs. pcs. pcs. pcs. pc. pc. m. unit

Item description CHB # 5 or 6 Portland cement Sahara waterproofing White sand Crushed gravel, 3/4" RSB, 10-mm diameter CWN, assorted, 1,2,3 Coco lumber, 2" x 2" x 12' G.I. tie wire, #16 Plywood, 1/4" x 4' x 8' Plywood, 1/2" x 4' x 8' Lawanit, 1/8" x 4' x 8' Concrete pipe, 8" diameter Stainless pipe, 8" diameter Ball valve, 1" diameter Screen wire, 1/2" x 1/2" burner gas stove (heavy duty)

Plan of a 6 cu.m. DSAC-Model biogas plant

(Adequate size for 30 heads of pigs or 2,000 heads of chicken)

Figure 47a. Lay-out 75


Figure 47b. Plan

Figure 47c. Longitudinal section

Figure 47d. Section of inlet pipe and hydraulic chamber Biogas Technology in the Philippines

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Chapter VI

TUBULAR POLYETHYLENE DIGESTER The Tubular Polyethylene Digester (TPED) developed by the Bureau of Animal Industry of the Department of Agriculture is

a biogas technology for small swine farmers. TPED is simple, cheap and easy to install. For a measly Php10,000-P15,000, a farmer can have TPED in his backyard. TPED can provide a steady supply of fuel for cooking, thus cut LPG expenses. In addition to this savings, foul odor of decomposing animal manure can be eliminated.

Major Parts of TPED Biogas Digester (Derived from Technology Adoption and Co mmercialization of Low - Cost and Environm ent Friendly Biogas System, Quirino State College)

TPED biogas system has the following six major parts: 1. Trench. This is where the digester is placed. This can be constructed in several ways; either with hollow block sidings dug in soil or placed on top of soil. 2. Digester . This is made of polyethylene bag where manure and urine are placed and where biogas is produced. 3. Safety valve. This is made of one liter capacity plastic bottle where excess gas evaporates to avoid gas reservoir from erupting. 4. Gas Reservoir. This is a polyethylene bag where the biogas produced is stored. 5. Heavy Wooden Object. This is placed on top of the reservoir when burner is used to provide pressure on the gas reservoir so that gas will flow to the burner. 6. Stove. This is where biogas is used. Biogas Technology in the Philippines

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Installation of TPED Biogas Digester Preparation of Trench

A trench may be constructed in several ways. Adopters prefer to construct a concrete trench to protect the digester from soil erosion which may damage the digester (Figure 48a).

Figure 48a. Concrete trench Trench can also be just dug in the soil without concreting it but the life-span of the polyethylene bag is at stake (Figure 48b).

Figure 48b. Trench dug in the ground 79


The polyethylene digester can be placed on top of the ground but should be fully protected (Figure 48c).

Figure 48c. Digester on top of the ground w/o trench When digging the trench it is important to observe the following: n

n

n

The sides and the floor should be smooth with no protruding stones or roots which could damage the plastic film. The floor should have a slope of about 25% from the inlet to the exit (this would be 25cm for a biodigester of 100cm length). The soil that is excavated should be moved away from the edges of the trench so that movement around the bio-digester during or after installation, or subsequent heavyrains, wil l not cause soil to fall onto the plastic.

Protection of the Polyethylene Plastic Digester and Gas Reservoir

The polyethylene plastic digester and gas reservoir must be protected against astray animals as well as children and falling

twigs. The digester and gas reservoir should be enclosed with screen or fence made out of indigenous materials to serve as protection to the structure (Figures 48d). Biogas Technology in the Philippines

80

Figure 48d. The funnel type entrance of manure with screen protection of digester Preparation of the Polyethylene Plastic Digester

1. Cut the polyethylene bag in accordance with the length of the trench prepared (usually from 8 to 10 meters). 2. Lay the plastic flat on a smooth surface then insert one into the other to double the polyethylene bag. Extra care must be observed to protect the plastic. 3. Install the gas outlet. Cut a small hole from the inlet on one edge of the tube. Fit the plastic washer (PVC card) into a small male PVC adapter and insert through the hole from the inlet to the outer portion of the plastic digester. Put another washer and rubber piece and fit it with the female adapter firmly. Cover the gas oulet with a piece of plastic to prevent the escape of air. 4. I nsert a 4 ” PVC pipe at one end of the plastic tube. Fold the plastic around the PVC pipe and tie it with rubber strip. Seal the inlet with plastic cover tied with rubber strip. 5. To fill the polyethylene tube with air, place the plastic cover at one end of the tube then grasp the other end with both hands

and open the plastic in front of an electric fan in order to inflate the polyethylene tube.

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6. Once the polyethyle ne bag is inflated, insert 1” PVC pipe covered with plastic and tie the folded end of the digester with rubber

strips to avoid escape of air. 7. Carry the tube c arefully and place it in the ditch or trench. P ut

the PVC pipe in 45 degrees inclination and fix it temporarily. 8. Fill the digester tube with 3/4 of water. For regular gas production, install a transparent plastic bottle of 1 to 2 liters capacity. Use a PVC Tee, 2 PVC of 1/2 diameter and about 30

cm long. Fix the gas outlet using the 1/2 diameter PVC pipe, a PVC elbow, 2.5 meters plastic hose, and a safety valve. Put a hose inside the bottle with 3 - 4 cm submerged in water to maintain the 3 psi capacity of the gas reservoir. Preparation of Gas Reservoir

The gas reservoir is made up of polyethylene bags around 3 meters long. This is connected near the safety valve and joined

by a PVC Tee. Put the gas reservoir horizontally in an elevated place and put a heavy object above the reservoir to give pressure

on it when the gas is in use. The heavy object is removed when gas is not in use to allow the gas reservoir to resume its original shape as the used methane gas is replaced. Methods of Constructing the Biogas System The method of constructing a TPED biogas system depends

on the location of the pig pen and the number of households using the biogas system. TPED biogas system models are illustrated in Figures 48e and 48f. For more detailed steps in constructing the digester, you http://www.wcasfmra.org/biogas_docs/ may visit this site: 5%20Vietnam%20Plastic%20Tube%20Manual%20Biodigester.pdf


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Figure 48e. First model

Figure 48f. Second model 83


Table 8. Materials needed for the construction of Tubular Polyethylene Digester

R ef er en ce s:

Avilla , H.F. et.al. 200 6. Bio ga s Te chn ology Develo pm en t in the Philippin es: Status an d Propects. Co untry Paper presented to the ASEAN Rural Energy Forum and Technology Exhibition. Be nig no , S.O. and H.K Ba nciles . 2000 . Tech no lo gy A d optio n a nd Comm erc ialization of Lo w Cost and Environment Friendly Biogas System. Maid en Issue. Ro d rig ue z, L. an d T.R. Pres to n. B io ga s Di ge ste r In sta lla tio n Man ua l. Un iversity o f Tro pica l Agriculture Fou ndation


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Chapter VII

COVERED LAGOON DIGESTER A covered lagoon digester is a large anaerobic lagoon with long retention time and high dillution

factor. Typically, this is being used with flush manure management systems that discharge manure at 0.5 to 2 percent solids. The in-ground, earth or lined lagoon is covered with a flexible or floating gas tight cover. They are not heated

Figure 49. Covered lagoon digester

and considered ambient temperature digesters. Retention time is usually 30-45 days or longer depending on lagoon size. Biogas production in the system tends to vary seasonally due to temperature fluctuations.

Components of Covered Lagoon Digester Solids separator . A gravity solids trap or mechanical separator

should be provided between the manure and the lagoon. Lagoons. Two lagoons are preferred; a primary anaerobic waste

treatment lagoon and a secondary waste storage lagoon. Floating lagoon cover . The most effective methane recovery system is a floating cover over all or part of the primary lagoon. Biogas Technology in the Philippines

86

Biogas utilization system . The recovered biogas can be used to produce space heat, hot water, cooling or electricity.

Covered Lagoon Design Variables Soil and foundation . Locate the lagoons on soils of slow-tomoderate permeability or on soils that can seal through sedimentation and biological actions. Avoid gravelly and shallow soils over fractured or cavernous rock. Depth. The primary lagoon should be dug where soil and geological conditions allow it to be as deep as possible. Depth is important in proper operation of the primary lagoon and of lesser importance in the secondary lagoon. Deep lagoons help maintain temperatures that promote bacterial growth. Increased depth allows a smaller surface to minimize rainfall and to cover size, which reduces floating cover cost. The minimum depth of liquid in the primary lagoon should be 12 ft. Loading rate, hydraulic retention time and sizing of primary lagoon. The primary anaerobic lagoon is sized as the larger of volatile solids loading rate (VSLR) or a minimum HRT. Volatile solid loading rate . The VSLR is a design number, based primarily on climate, used to size the lagoon to allow adequate time for bacteria in the lagoon to decompose manure. Minimum hydraulic retention time. The VSLR procedure is appropriate in most cases, however, modern farms using large volumes of processed water may circulate liquids through a primary lagoon faster than bacteria can decompose it. To avoid this washout, a minimum hydraulic retention time (MINHRT) is used to size the lagoon. Primary lagoon inlet and outlet. The primary lagoon inlet and outlet should be located to maximize the distance across the lagoon between them. 87


Rainfall. Rainfall is not a primary factor in determining the potential success of a covered lagoon. In areas of high rainfall, a lagoon cover can be used to collec t clean rain falling on the cover

and pump it off to a field. In areas of low rain, a lagoon cover will limit evaporation and loss of potentially valuable nutrient rich water.

Cover materials. Many types of materials have been used to cover lagoons. Floating covers are generally not limited in dimensions. A floating cover allows for some gas storage. Availability of materials, serviceability, and cost are factors to be considered when choosing a cover material. Cover installation techniques. A lagoon cover can be installed in a variety of ways depending upon site condition.

Full perimeter attachment. The entire lagoon surface is covered and the edges of the materials are all attached to the embankment. Completely floating or partially attached cover. The cover may be secured on the embankment on one to three sides or the whole cover can float within the lagoon. All or some of the sides may stop on the lagoon surface than continuing up the embankment.

Operation and Maintenance of Covered Lagoon Digester Primary Lagoon Operation. The proper design and construction of a primary lagoon leads to a biologically active lagoon that should perform year round for decades. Any change in operation will most likely be due to change in farm operation resulting in an altered volatile solids loading or hydraulic load to the lagoon. The owner should make a weekly visual inspection of the lagoon level.


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Primary lagoon maintenance.

Minimal maintenance of the

primary lagoon is expected if the design volatile solids and hydraulic

loading rates are not changed. Lagoon banks should be kept free of trees and rodents that may cause embankment failure. Weeds and cover crops should be cut to reduce habitat for insects and rodents. Occasional plugging of inlet and outlets can be expected. Accumulated sludge should be removed every 3 to 5 years. Sludge can be removed by agitating and pumping the lagoon or by draining and scraping the lagoon bottom. Cover operation. Operating a lagoon cover requires removing the collected biogas from below the cover regularly or continuously. Large bubbles should not be allowed to collect. If the cover is designed to accumulate rainfall for pump off, accumulated rainwater should be pumped off. Cover maintenance. The cover should be inspected weekly for rainwater accumulation, tearing, wear, and proper tensioning of attachment ropes. The rainwater pumpoff system should be checked after rainfall and maintained as needed.

The Covered In-Ground Anaerobic Reactor (CIGAR) In the Philippines, the Covered In-Ground Anaerobic Reactor (CIGAR), a type of covered lagoon digester, was introduced by PhilBIO in the year 2000 when it constructed its first biogas project in Rocky Farm (Figure 50). The CIGAR (Figure 51) effectively breaks d own organic contaminants through

a multi-step biological treatment of the waste-water in the absence of oxygen. High density polyethylene (HDPE) liners and covers are used to provide for an air-tight system and to prevent leachate from percolating through the ground and polluting local ground water aquifer resources.

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The wastewater, after passing the CIGAR system, resulted to around 95% destruction of harmful biochemical oxygen demand (BOD) and 80% reduction of chemical oxygen demand (COD). Suspended solid is reduced and color is improved in CIGAR system. The digester

is designed to maintain a 30day retention time and temperature of 35 o C to effectively reduce pathogenic materials. The effluent is then

sent to a final treatment lagoon where normal facultative aerobic process predominates. Figure 50. CIGAR at Rocky Farm

Figure 51. The CIGAR system Sourc e:

http://cdm.unfccc.int/usermanagen t/FileStorage/5HHJ719OINSKCQ53PPTFPANBANH91I


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Biogas is also produced in a CIGAR system. The biogas produced is used to generate electricity for use on-site. A biogas-

fueled generator is usually installed in the farm providing the power need of the farm. Surplus biogas are flared rather than released to the atmosphere until such time that structural barriers

are removed to allow the export of any surplus electrical energy to the local distributing grid.

Figure 52. Lagoon digester and biogas handling The Universal Robina Corporation (URC) RF 12 in Bulacan is the largest biogas project done by PhilBIO with 1.08 MW power plant (Figure 53).

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Figure 53. URC RF 12

Figure 54. Lagoon effluent R ef er en ce s:

http://cdm.unfccc.int/usermanagent/FileStorage/5HHJ719OINSKCQ53PPTFPANBANH91I http://pcierd.dost.gov.ph/index2.php?option=com_docman&task=doc_view&grid=21&Itemid=41 http://www.biogaspsu.edu/coveredlagoon.html http://www.calstart.org/info/publications/Biomethane_from _Dairy_Waste_Full_Report.pdf http://www.philbio.com.ph


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Chapter VIII

OPERATION AND MAINTENANCE OF BIOGAS DIGESTER Like any other equipment, the biogas should be properly

maintained to achieve efficient operation. A properly built structure and sufficiently available materials may not produce the desired results due to faulty operation and/or maintenance.

Initial Loading 1. Starter/Seeding. “

The initial raw materials known as

starter ” should contain slurry with high bacteria population.

About 5 - 10% of the total slurry volume should be added when the digester is about 25% full. 2. Cattle dung is a good starter since cattle have methane producing bacteria in their stomachs. Starter can also be made from any manure by adding to its 5-10% “old” slurry obtained from another digester or when cleaning the digester. Starter can also be prepared by storing manure in a container.

3. Filling the digester. The digester should be filled as quickly as possible. The following steps should be kept into consideration: a) Be sure to open all valves to relieve any pressure buildup in the digester dome before putting any slurry into the digester. It is advisable not to connect the piping system to the digester when loading. b) Mix manure and water thoroughly until there are no more “lumps”. This will increase gas production since the bacteria will have more contact surface with the manure. Biogas Technology in the Philippines

94

c) Fill the digester with slurry up to beam level. This is the same level as the outlet chamber floor. d) Do not load any new slurry to the digester until at least 3 days after burnable gas is produced. 4. If the above conditions are not possible, just let the slurry flow into the digester until such time that the digester is filled up to the level of the outlet chamber floor. The necessary bacteria will grow biologically and biogas can be produced in 30 to 40 days. 5. The following materials should not enter the digester: a) Earth or sand; b) Straw, grasses, leaves, etc. – remove all floating materials at the mixing pit before allowing them to enter into the digester. These materials will float on the slurry surface

and may cause problem. c) Oil, soap, detergent, disinfectant, etc. – these materials will disrupt bacteria activity and may even kill the b acteria.

Regular Loading About 1 liter of water is added to every kilogram of manure. The slurry should be mixed thoroughly until the right consistency is obtained. However, in actual practice, there is no fixed water-manure proportion since this will depend on the type of manure being used and its moisture content. The technique will be developed through experience. The loading of materials should be done regularly. Ideally, it should be daily. The amount of slurry should be in accordance

with the requirement of the particular digester volume and its retention time. Less slurry being loaded would result to lower gas production whereas excessive slurry would result in raw materials wastage since slurry will not be fully digested.

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The loading of new slurry materials displaces an equal volume of effluent to the outlet chamber. This effluent must be removed otherwise the digester would be overloaded. The correct digester level is that at zero gas pressure, the slurry should be at

the level of the outlet chamber floor.

Stirring/Agitation of Slurry Mechanically disturbing the slurry inside the digester with the use of stirrer performs two vital functions: first, to stimulate

bacterial activity and second, to break the “scum” layer which forms a mat of vegetable/organic matter at the slurry surface and thus, restricts the gas flow. If left undisturbed, the scum would get thick and harden, which may require opening the digester to remove it. Stirring should be done daily

–

about 3 to 5

minutes in the afternoon. The stirring should be 360 o in one direction and 360o in another direction. For the DSAC-Model, there is no need for stirring since the system operates on displacement principle (see Principles of Operation on page 58).

Condensate Removal The condensate or water that settles in the piping system must be removed monthly since condensate accumulation may obstruct gas flow. The condensate removal may be done by lifting

the gas pipe so that the water in the pipe will be drained back into the digester. Another method is to provide the gas pipe system with condensate trap for easy removal of water.

Servicing Scum Problem Scum very seldoms developed in a DSAC-Mo del biogas plant.

In other designs where this is a perennial problem, the following are the steps that should be undertaken:


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1. Release all gas in the digester. Manometer reading should be zero. 2. Disconnect the gas piping closest to the digester. 3. Remove manhole (if present in the structure). 4. Inspect the scum layer and check its thickness. 5. Remove scum manually with buckets through the manhole.

CAUTION: In removing the scum, be cautious about the pre se nce of fir e nearb y. Smo kin g near the dig ester is dangerous. The digester may still contain gas and may explode.

Periodic Maintenance of the Digester Unlike the DSAC-Model biogas digester, some digester models

need periodic maintenance. In these cases, the digester may need to be emptied at least once a year to remove the settled sludge and other inorganic solids, like sands and stones that accumulate at the digester bottom. The materials are removed manually through

the manhole with the use of buckets or pumps. This is also an occasion to check for possible leaks or structural damages. Take precaution when entering the digester. There are poisonous gases inside. Also, complete emptying of the digester should be done if the following conditions occur: a) Stirring becomes too difficult due to heavy accumulation of inorganic solids (sand, pebbles, etc.) and/or presence of thick scum. b) Gas production ceases completely. This may be due to the introduction of toxins (detergents or disinfectants) into the slurry.

c) Gas production slows down despite regular daily loading and stirring. There may be leaks in the structure. Regular cleaning of the inlet tank should also be done, as well as checking for leaks in the pipes and the digester. 97


Table 9 shows the possible remedies to most common problems encountered by biogas plant users. Table 9. Trouble shooting of biogas plant P rob le m G a s p r e s s u re d o e s n o t rise

C au s e V e ry fe w b a c te ria

R emed y In cre a se the n um be r of b a c t e r ia b y s e e d i n g o r a d d in g s lu d g e f r o m a n e x i s ti n g digester

L ac k o f t im e

F o r co ld w eat h e r, w a it fo r a few weeks.

L e a k a g e a t ga s p i p e o r g a s c o n n e c t i on

Locate the leakage and pu t soap suds on the pipe/connection.

G a s t ap op e n

U n u s e d g a s t a p s h ou ld b e checked and closed.

T e m p era ture is low .

In c re ase t e mp er at ur e b y p r o v i d in g c o v e r .

P re se nc e of s cum

S tir t h e s lu rry in t he d ig e ste r.

Too m uch feeding or too l i t tl e f e e d i n g

P u t t h e r ig h t a m o u n t o f ra w materials.

P r e s e n c e o f i n h i b i t o rs (detergents, chemicals, etc.)

Avoid the entrance of these materials into the digester. Continue daily adequate loading.

R a w m a t e r i a ls t o o t h i c k o r A d d m o r e w a t e r t o d i l u t e t h e t o o t h i n. r aw m a t e r i a ls . G a s d o e s n ot bu rn

P o or q ua lity

In itia l g as c o nt a in s a ir, c a r b o n d i o x id e a n d o t h e r in f l a m m a b l e g a s e s .

Presence of air in the gas pipe

R e l e a s e a i r in t h e g a s p i p e .

F l a m e i s u n s t a b le ( l o n g , P o or g as q ua lit y and w eak, small and pulsating) In co r re c t g a s p r es s ur e

In itia l g as c o nt a in s a ir, c a r b o n d i o x id e a n d o t h e r in f l a m m a b l e g a s e s . C o rr ec t g as p re ss u re to a b o u t 7 5 t o 8 5 m m w a te r .

Gas jet in stove is blocked Clean gas jet Presence of condensate w a t e r i n t he g a s l in e . R a w m a t e r ia l s d o n o t flow into the digester.

Inlet/outlet pipe is clogged.

D ig e s te r pl an t o v er f lo w . O u t le t pi p e i s c l og g e d .

Remove condensate and provide wat er trapping service. C l e a n t h e p i p e b y i n s e r t in g a p o le i n t o t h e p i p e s . C le a n t h e p ip e by in s e rt in g a p o le i n t o th e p i p e s .

S lu rry is to o th ick .

A d d m o re wa te r t o im pro ve dilution.

O u t le t c ha m b e r to o h i gh .

O u t le t o f h y d r a u li c c h a m b e r s h o u l d b e lo w e r e d b y e le v a t i n g t h e i n l e t.


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Chapter IX

BIOGAS UPGRADING Biogas consists of methane (CH 4) carbon dioxide (CO 2) along with some trace gases such as water vapour, hydrogen sulfide (H2S), nitrogen, hydrogen and oxygen. Carbon dioxide and trace gases such as water vapor and H2S must be removed before the biogas can be used because: n n

the hydrogen sulfide gas is corrosive water vapour may cause corrosion when combined with H 2S on metal surfaces and reduce the heating value

Energy recovery from biogas is becoming more common, but the process are hampered with the presence of hydrogen sulfide (H2S). Hydrogen sulfide (H2S) is a colorless, very poisonous gas. It is flammable and forms explosive mixture with air (oxygen). H2S itself has an offensive odor of “rotten eggs ” at concentration as low as 50 parts per billion by volume (ppbv) and is toxic at concentrations above 100 parts per million by volume (ppmv). H2S is a health and safety hazard, and when combined with carbon dioxide (CO 2) and water vapor (H2O), corrodes plant equipment such as boilers and piping, and can ruin powergenerating equipment. A combustion product of H2S is SO2. This makes the exhaust gases very corrosive (sulphuric acid) and contaminates environment (acid rain). High levels of H 2S can also interfere other processess such as killing useful bacteria in an anaerobic digester. Reducing H 2S offers cost savings associated with less maintenance, increased process and energy efficiency, and reduced toxic emissions.


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The incombustible part of biogas, CO 2, lowers its calorific value. On the average, the calorific value of biogas is 12.5 MJ/ m3. By removing the CO2 from the biogas, the calorific value is increased. Stripping CO2 and H2 S from biogas is so called upgrading

of biogas. By upgrading biogas to natural gas quality, containing approximately 88% CH 4 , it is suitable for more advanced

applications in which the heat is not wasted, resulting in a higher efficiency.

Determination of the Hydrogen Sulfide Content in Biogas H2S content of the gas can be measured by the following

methods.

Laboratory Method . H2S content of gases is usually measured iodometrically using cadmium acetate. Lead Acetate Method . A simple way of determining the presence

of H2S in biogas is a test with lead acetate paper. A piece of

paper soaked with lead acetate solution is held in the gas stream

for a short time. The strip of paper will turn black if H 2S is present. The difficulty with this method is its high sensitivity which means that even a very small amount of H 2S can be

detected. A small amount of H2S, however, is not an indication of

greatly reduced efficiency of the desulphurization. Simple desulphurization plants may still posses an adequate purifying performance.

Detection with Iodine Solution . Another simple method for detecting H2S is with an alcoholic solution of iodine which is often available in first aid kits. A small amount of biogas is carefully

introduced into the iodine solution. If H 2S is present the reddish brown solution will decolour. The formation of elementary sulphur causes a milky turbidity. 101


Test-tube Method . The test-tube method is a very exact and simple method of determining the H 2S concentration in biogas.

Suitable tubes are available for measuring the concentration in both raw and purified gas. The gas detector apparatus (ca. 450,DM) and the individual test tubes (ca. 5,- DM each) are relatively

expensive. Also, the test tubes can only be preserved for a limited

time. This method is only expedient in the regional biogas extension service or similar advisor y s ervices. This apparatus could then be used to provide empirical field values for individual

plants. The intervals for recharging the purifying agent can then be laid down. There is no simple, cheap test method available as of now.

For this reason a close control of the desulphurization plant is strongly recommended.

Biogas Upgrading Techniques Techniques of upgrading biogas in large applications are: chemical absorption, high pressure water scrubb ing, pressure swing

adsorption, cryogenic separation and membrane separation. Chemical absorption of H2S into iron-chelated solutions offers a highly efficient removal of H2S from a gaseous biogas stream. The iron-chelated solutions function as a pseudo-catalyst which can be regenerated. The H2S is removed almost completely and converted to elemental sulphur. After the absorption process a scrubber is needed to remove the CO 2 (Figure 55a).

High pressure water scrubbing is based on the physical effect of dissolving gases in liquids. In a scrubber, CO2 as well as H2S, dissolves in the water while CH4 does not because of their difference in solubility. This makes it a very simple process (Figure 55b).


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Pressure swing adsorption separates certain gas species from a mixture of gases under pressure, according to the species ’ molecular characteristics and affinity for an adsorption material. The adsorption material adsorbs H 2S irresistably, and this is poisoned by H2S. This upgrading system consists of four adsorber vessels filled with adsorption materials (Figure 55c). In cryogenic separation , the different chemicals in biogas

liquefy at different temperature-pressure domains allowing for distillation. Typically, a temperature of -170oC and a pressure of 80 bar is used. Producing pure CH 4 from biogas is done by cooling and compressing the crude biogas to liquefy CO 2 which then easily

separated from the remaining gas (Figure 55d).

In membrane separation , CO2 and H2S will pass through a

certain membrane while CH 4 does not. This is also a very simple technique since only a compressor and a membrane are needed. However, this technique is expensive and results to a low methane

yield (Figure 55e). Of the many processes available, only the ‘dry process ’ is suitable for small biogas plants. The desulphurization of biogas is based on a chemical reaction of H 2S with a suitable process. Lime Process . The oldest process is the desulphurization of gases with quick lime, slaked lime in solid form or with slaked

lime in liquid form. The process using quick or slaked lime has not been applied on a large scale for a long time. The large amounts of odourous residue that are produced cannot be satisfactorily disposed of. The handling of large amounts of dissolved or suspended slaked lime requires elaborate equipment.

Large concentrations of CO 2 which are present in biogas make the satisfactory removal of H2S difficult. The CO2 also

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reacts with the quick and slaked lime and uses it up quickly. The Ca(HCO 3)2 formed reacts with Ca(SH) 2 which is formed by the reaction of H2S with Ca(OH)2 thus, resulting in the reoccurance of H2S.

By Ferrous Materials. Ferrous materials in the form of natural soils or certain iron ores are often employed to remove H2S. The ferrous material is placed in a closed, gas tight container (of steel, brickwork or concrete). The gas to be purified flows through the ferrous absorbing agent from the bottom and leaves the container at the top, freed from H 2S. Chemistry. The absorbing material must contain iron in

the form of oxides, hydrated oxides or hydroxides. These react as follows:

2 Fe(OH)3 + 3 H2S Fe(OH)2 + H2S

Fe2S3 + 6 H2O FeS + 2H2O

This process terminates, of course, after some time. The greater part of the iron is then present as a sulfide. Regeneration. By treating the sulphidized absorbent with atmospheric oxygen, the iron can be returned to the active oxide

form required for the purification of the gas: 2 Fe 2S3 + 3 O2 + 6 H2O 2 FeS + O2 + 2 H2O

4 Fe(OH)3 +3 S2 2 Fe(OH)2 + S2

The used absorbent can, therefore, be

“regenerated ” .

This regeneration cannot be repeated indefinitely. After a certain time the absorbent becomes coated with elementary sulphur and its pores become clogged. Purifying absorbents in gasworks (coke

plants) acquire a sulphur content of up to 25% of their original weight, i.e. 40% sulphur by dry weight.


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Figure 55a. Flow diagram for chemical absorption

Figure 55b. Flow diagram for high pressure water scrubbing

Figure 55c. Flow diagram for pressure swing absorption 105


Figure 55d. Flow diagram for cryogenic separation process

Figure 55e. Schematic representation of membrane separation Biogas Technology in the Philippines

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Biogas Purification Process by ITDI The biogas purification process developed by the Industrial Technology Development Institute (ITDI) consist of biogas digester, compressor, series of scrubbers, storage tank for scrubbed biogas,

converted gasoline fed generator, and appliances for electricity utilization (Figure 56).

Figure 56. Biogas purification process by ITDI

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The scrubbers consist of four units of 8 inches diameter PVC pipes each of 50 liters capacity. It is either packed with sodium hydroxide (NaOH) for the removal of CO 2 and iron filings for the removal of H2S. Performance efficiency of the scrubber system is shown in Table 10.

Table 10. Performance efficiency of ITDI scrubber system U n trea te d B io g as CO 2

CH 4

Heating Value

T re ated (S cru b b ed ) B io g a s Heating Value CO 2 CH 4

3

3

(BTU/ft ) 29.1

30.5 29.1

40 40 31

29 30 33

70.9 69.5 70.9 60 60 69 71

70 67

695 681

695 588 588 676 696 686 657

(BTU/ft ) 1.0 1.5 1.0 0.4 0.5 0.2 0 .1

0.5 4.5

99 98.5 99 99.6 99.5 99.8 99.9 99.5 95.5

970 965 970 976 975 978 979 975 936

CO 2 Removal Rate (%) 96.5 95.1

96.5 99 99 99.4 99.7 98.3 86.4

R ef er en ce s:

http://www.fao.org/do crep/T0541E/T0541E0b.htm http://www.scielo.br/scielo.php?script=sci_arttext&pid=s0104-66382004000300006 http://www.watersanitationhygiene.org/References/EH_KEY_REFERENCE S?Sanitation/ BioGas/Purification Hu llu , J.D. e t a l. 2008. C om pa rin g d iffe rent b io ga s u pg ra d ing tech niq ue s. Inte rim Re po rt. Silverio, C.M. Purification of m ethane from b iogas d igester and con version for electricity generation (http://8th-astw.dost.gov.ph/alt_energy/ITDI_BIOGAS.pdf


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Chapter X

BENEFITS FROM BIOGAS TECHNOLOGY There are two (2) kinds of benefits that can be derived from using the biogas system. First are the tangible benefits in which we can put money value on it. These include energy generation and production of feed materials and high quality fertilizer for crops. In most cases, these benefits are in the form of savings because the amount allocated for the purpose was not spent because of available biogas and its by-products. However, in larger applications, the technology becomes a source of income especially when used in producing high quality fertilizer.

The other type of benefit is the intangible benefit which we cannot put money value such as promotion of the conservation of natural resources by not cutting trees for firewood, controlling pollution by proper waste disposal, thereby reducing odor, ground

and surface water contamination and reduction of greenhouse gas emissions. These benefits are more rewarding because man is given the right to live in a fresh, clean and beautiful environment.

Economic Assessment of DSAC-Model Biogas Digester The generated biogas is a potential energy in which the owner has the option for use. He may use all of it or just part of it depending on his particular need. The extent of his actual use of biogas will spell out the magnitude of his savings. The financing support for biogas generation is necessary for the success of the system. The investment is capital intensive

at front end but the long term benefits of the technology is Biogas Technology in the Philippines

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worth supporting the development. Borrowed capital can be amortized from the savings enjoyed in the system. The technology

level or skills necessary to adopt the technology is within the competence of the average Filipino farmers. The raw material for biogas is agricultural waste but the end products are vital to improving the quality of life. To be able to visualize what will happen to our money invested on biogas works, we have to consider all the benefits derived from the system and evaluate it against the cost of using the system. For our discussion, we will use an 8 cu. m. DSAC-Model biogas digester to be used in a piggery project with 30 hogs capacity.

Cost Component of the Biogas System

A. Initial Investment Cost The investment is the initial capital used in the construction and installation of the system, including the excavation. Investment cost for a 8 cu.m. biogas digester is summarized below. Item Assumptions Investment Cost Biogas System Excavation

P10,000.00/cu.m. P450/cu.m. @12.5cu.m.

P80,000.00 5,625.00 ———————

Total

P85,625.00

B. Operating Expenses Operating expenses refer to the amount used in operating the biogas system which include labor, repair and maintenance, interest on investment and

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depreciation. The biogas worker is required to check the system

at least two days per week. If he is paid with P279.50 per day (site basis), then the total labor cost per year is P29,068.00. Annual repair and maintenance is estimated at 3% of the initial investment since the digester has no moving parts. The interest rate is 37.92% which is based on the prevailing bank interest rate assuming that the money is loaned. Depreciation cost is estimated using a straight line method and a 25-year life span of the digester with zero salvage value. Operating expenses is summarized below. Items 1. 2. 3. 4.

Cost

Labor Repair and Maintenance Interest on Investment Depreciation Total

P 29,068.00 2,568.75 16,234.50 3,425.00 ———————-— P 51,296.25

Energy Value of Biogas

a) Fresh manure production

= 30 hogs x 3 kgs/day = 90 kgs/day = 90 li/day = 32.85 cu.m. per year

b) Volume of digester required = 90 li/day x 2* = 180 li/day x 40 days RT = 7200 li = 7.2 cu.m. c) Biogas production (50% methane production)

= 7.2 cu.m. x 50% = 3.6 cu.m. per day = 1,314 cu.m./yr

* (1:1 manure-water ratio)


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In this case, the volume of digester required is 7.2 cu.m. It is recommended that we use an 8 cu.m. biogas digester. d) Equivalent in conventional energy 1 cu.m. of biogas = 3.47 kgs of firewood = 0.45 kg LPG d.1. firewood = 3.47kg/u.m. biogas x 1,314 cu.m./yr = 4,559.6 kgs/yr Peso equivalent = P22,798.00 d.2. LPG = 0.45kg/cu.m. biogas x 1,314 cu.m./yr = 591.3 kgs/yr Peso equivalent = P30,103.00 Since we are evaluating the economic performance of the digester, we have to consider everything that can be generated from the digester as benefits. We assumed that the family uses biogas as substitute for either firewood or LPG, and therefore calculated the value of firewood or LPG saved for a yea r. Majority

of the society are now using LPG instead of firewood, therefore, we will consider the amount saved from the use of biogas as replacement for LPG. However, the volume of LPG equivalent of biogas produced is very large (equivalent to more than 53 LPG tanks). Therefore, we assumed that only 165 kgs of LPG (15 tanks of LPG in a year) are consumed and counted as savings in fuel. Other biogas produced are sold to three different neighbors

at the rate of half of price of LPG and in assumption that they are consuming one tank of LPG per month. In this case, the three neighbors will be paying P280.00 per month for their biogas consumption. Peso equiv =(165 kgs/yr x P50.91/kg)+(P280/mo x 12mo/yr x 3 neighbors) = P18,480.15 113


The economic value of recovered sludge as feed materials and organic fertilizer follows the same format of substitution and extent of use. As much as 30% of the feed requirements can be substituted by sludge and that sufficient organic fertilizer (as much as 40%) can be recovered from the digested sludge. In this example, we will use 15% feed requirement substitution and 20% organic fertilizer recovery. e) feed material recoverable from sludge e.1. Total feed consumption of hogs = 18,000 kgs/yr e.2. Amount of feed materials to be substituted with sludge (15%) = 2,700 kgs/yr e.3. Peso Equivalent (P23/kg) = P62,100 f) Organic fertilizer from sludge f.1. Volume of digested sludge = 32.85cu.m./yr f.2. Organic fertilizer recovered (20%) = 6.57 cu.m./yr = 6,570 kgs/yr f.3. Peso Equivalent (P 5/kg ) = P32,850.00 f.4. Processing Cost (50%) = P16,425.00 f.5. Net Savings/Income = P16,425.00 g) Total Savings/Income = Saving/Income in Energy + Feeds + Fertilizer = P18,480.15 + P62,100 + P16,425.00 = P97,005.15 h) Net Savings = P45,708.90 i) Return on Investment = 53.40% j) Payback Period = 1.87 years


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Chapter XI OPPORTUNITIES AND BARRIERS OF BIOGAS TECHNOLOGY Today, recognition of biogas technology as a solution to pollution problem is more important than energy recovery. Compliance to environmental regulations and avoidance from complaints of local people are the major drivers influencing the owner to invest in the technology. The economic advantage of recovering and using biogas as energy source is just secondary reason for having a digester. The widespread acceptance and dissemination of biogas technology has not yet materialized in the country. One main reason, often mentioned, is the required high investment capital.

But often the reason for failure is the unrealistically high expectations of potential users. Biogas technology cannot solve every problem of a farm, a village or a big animal production unit. Biogas technology is not a universally accepted technology like transistor radio. A biogas plant has to fit into existing farming,

production or waste disposal systems. Attempts to make the system fit to the biogas plant will res ult in expensive and frustrating

failures. Biogas technology has many competitors. Energy can be produced by fuelwood plantations (with other positive sideeffects), by solar systems, hydro-power and other renewable energy technologies. Producing high quality fertilizer can be done in other cheaper way such as composting which are even closer to traditional techniques. What makes biogas an attractive

option is the fact that this technology can provide solutions to a variety of problems simultaneously as “waste-treatment facility ” and as an “energy-generating device”. Biogas Technology in the Philippines

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Barriers in the promotion of biogas technology can be categorized into three: 1) financial, 2) information, and 3) technical. Barriers that fall under the financial aspect are: - high investment cost - lack of institutional support - limited access to financing schemes - lack of incentives to technology adaptors - lack of local government policies to support technology promotion in the countryside Meanwhile, the barriers that fall under the information aspect are: - unclear delineation of roles of agency in NRE - technology gap between the users and the technology itself - poor public image of the technology - inadequate information - absence of a databank Finally the barriers that fall under the technical aspect are:

-

lack of service standards lack of experiences on technology adoption lack of service technicians lack of biogas engineers and contractors

Refe rence s:

______. Biog as Dige st Volum e 1: B io gas B asics. ISAT Dilid ili , J .Q. e t a l. 1998. Techno lo gy Valid atio n o f B io ga s Te chno logy and Its Utilization in the Philippines. Terminal Repo rt. CvSU-ANEC . www. adb.org/Clean-Energy/documents/PHI-PFS-Biogas-SwineWaste.pdf ______. 2004. T he Philipp ine Re co mm en ds fo r A gricultural Waste Processing and Management. PCARRD.

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Appendices


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Appendix A

Utilization of Biogas Sludge as Feed Substitute for Hogs The study was cond ucted by: C. A. Polinga, J. Q. Dilidili, R. S. Sangalang, E. E. Po ling a, R. P. Ar ar ao and R. R. Ma ra siga n - 1996

Abstract The study aimed to: utilize digester sludge as feed substitute for fattening hogs; determine the effects of substituting

sludge on feed intake, length of fattening period and carcass quality; and determine the optimum level of sludge susbtitution for better growth performance of hogs. Completely Randomized Design (CRD) was used, with three treatments and two replications. The treatments were: T1 = 15% sludge substitution; T2 = 30% sludge substitution; and T3 = control (no sludge substitution). Results of the study revealed that growth and development

of hogs fed with sludge is comparable to that fed with 100% commercial feeds. Also, the carcass yield of hogs fed with sludge is not significantly different from hogs fed 100% commercial

feeds.

Introduction Environment pollution as a consequence of livestock production is becoming a serious problem. When animal manure is treated to prevent pollution but not utilized for other purpo ses, production expenses can increase considerably. At the same time,

manure which is considered a renewable natural resource is just wasted. Livestock farming should end up not only at marketing but should also extend to the utilization of animal wastes.


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The development of biogas digester partly solves energy problems as well as environmental pollution in the country. As a result of this technology, various studies have been conducted to maximize the use of the products of biogas technology - the biogas and the sludge. The Biogas Research Training Center for Asia and the Pacific

in Chengdu, China conducted a study on the supplementation of anaerobic digested effluent to animal feeds. Although preliminary findings indicated a certain degree of acceptance, it is not e nough

to easily adopt the technology since some important factors like breed/variety of pigs, environmental conditions and kind of fermentation materials are relative from each locality. Hence, a verification trial on the use of biogas sludge as feed supplement for hogs was conducted. It aimed to utilize digester sludge as feed substitute for hogs; determine the effects

of substituting commercial feeds with sludge on the feed intake, length of fattening period and carcass quality of hogs; and determine the optimum level of sludge substitution for better growth performance of hogs.

Materials and Methods A. Experimental Animals

Six piglets were used in the study. These were divided into three test groups and grown-finished for 5 months. The piglets in each test group had similar initial weights. The two test groups received the digester sludge substitute while the last test group was the control group which received the basic

ration (100% commercial feeds).

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B. Biogas Digester Sludge The biogas digester sludge used in this study was obtained

from a 30-m3 biogas plant located at the new piggery project of the Don Severino Agricultural College (DSAC). Continuous pH monitoring of the biogas sludge was done everyday during the entire duration of the experiment. Newly gathered sludge was filtered first before being added to the animal feeds to eliminate the impurities present in the sludge. C. Experimental Feeds and Feeding

Sludge was supplemented to the basic feed ration (commercial feed) of the hogs in the two test groups. The digester sludge was added to the feed according to the feed consumption of animals. The first group was fed with high level of digester sludge, 30% by weight of feeds, while the second test group was fed with medium level of digester sludge, which was 15% by weight of feeds. The control group received

the basic feed ration (100 percent of commercial feeds). The type of commercial feed given to the two test groups was exactly the same with that of the control group. Wet feeding method was followed since pigs do better on wet feed than on dry feed (Cullision, 1987). The animals were fed twice a day, in the morning and in the afternoon. D. Data Gathered

The following data were gathered: monthly liveweight (kg), liveweight gain (kg), daily consumption (kg) of the animals, feed conversion efficiency (%) of the animals, and the pH value of the gas produced.


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Gain in weight (kg) was computed using the formula: GW = W2-W1

where: GW = gain in weight, kg W1= weight of the animal in the previous month, kg Feed Conversion Efficiency was computed using the formula: GW FCE=

x 100 FC

where: FCE = feed conversion efficiency, % GW= gain in weight, kg FC = feed consumption of the animal during that month, kg Carcass quality was expressed in terms of slaughter weight (kg), carcass weight (kg), dressing percentage, carcass length (cm), and backfat thickness (cm). Dressing percentage was computed using the formula: carcass weight Dressing Percentage =

x 100 slaughter weight

Carcass length was measured from the shoulder of the hog to the end of its ham. Backfat thickness was determined by using a ruler. This was measured in three points of the hog ’s back: one in the midline and the other two, each 1 1/2 to 2 inches (3.8 - 5.0 cm) from the midline to front or rear.

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The data gathered were subjected to Analysis of Variance. Means were compared using Duncan ’s Multiple Range Test (Gomez

and Gomez, 1976). E. Results and Discussion Gain in Weight

The monthly average weight and gain in weight of the animals are shown in Tables 1 and 2 .

The results indicated that the growth respo nse of the animals fed with sludge as feed substitute is as normal as the animals fed

with basic ration of 100 percent commmercial feeds. There were no significant differences (P>0.01) among treatments. The result implies that hog raisers can substitute 15 to 30 percent of the feed requirements with biogas sludge. This is tantamount to 15 to 30 percent savings in feeds without affecting the growth and development of the animals and will eventually result in a 15 to 30 percent additional income. Table 1. Monthly average weight of hogs given diets partly substituted with biogas digester sludge, kg Age, months Initial weight 1 2 3 4 5

Treatment 15% 30% 18.00 20.50 30.25 32.50 41.40 42.90 58.30 60.25 77.05 81.70 90.60 92.00

Control 16.00 28.50 39.45 57.10 80.95 91.00


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Table 2. Monthly average gain in weight of hogs given diets partly substituted with biogas digester sludge, kg Ag e, mo nths 1 2 3 4 5

Treatment 15% 30% 12.25 12.00 11.15 10.40 16.90 17.35 18.75 21.50 12.95 10.30

Co ntro l 12.50 10.95 17.65 23.85 10.05

Feed Conversion Efficiency The feed conversion efficiency was observed in hogs fed

with 100 percent commercial feeds, although it was not significantly different (P>0.01) from the other treatments. This was followed by hogs fed with 15 percent sludge sub stitute

and the least was on hogs fed with 30 percent sludge substitute with 24.53 and 24.16 percent, respectively. Table 3. Mean feed conversion efficiency of hogs given diets partly substituted with biogas digester sludge, % Treatment 1 2 3

Replication 1 2 12.25 12.00 11.15 10.40 16.90 17.35

Total

Mean

12.50 10.95 17.65

24.53 24.16 26.22

Carcass Quality

The summary of carcass quality evaluation is shown in Table 4. The hogs given diets substituted with sludge gave comparable carcass quality to that of hogs fed with the basic ration of 100 percent commercial feeds.

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Table 4. Summary of carcass quality evaluation of hogs given diets partly substituted with biogas digester sludge

Conclusion

Based from the results obtained, it is concluded that susbtituting sludge to the feed ration of hogs has no adverse effect on their growth and development. Likewise, the substition

of 30 percent sludge (by weight of feeds) to the feed ration of hogs gives a desirable result since the amount of commercial feeds that would be consumed by hogs would be lessened by as much as 30 percent. Finally, the results proved that the sludge

could substitute the necessary feed and nutrient requirement of hogs. Recommendations

Based from the results, the following are highly recommended: substitution of sludge to the feed ration of hogs at the amount of 30% by weight of feeds; further study on the utilization of sludge as feed substitute of hogs using higher levels to test the maximum level at which the animal would gain better

performance; and study on the utilization of sludge to the feedstuff of other farm animals. Biogas Technology in the Philippines

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Appendix B

Wellisa Farms Waste to Energy Project It is common knowledge that majority of farms (commercial as well as backyard) in the Philippines lack proper waste treatment facilities. This is a complex problem when the total number of pigs consumed per year is around 12 million

heads. This amounts contributed to severe contamination of surface and groundwater resources, bes ides air and land pollution

issues. Wellisa Farm in Tayud, Consolacion, Province of Cebu, is an exception to this situation in terms of waste management as well as energy utilization. The farm is owned and operated by Mr. Wellington Chanlim, a leading entrepreneur in the agro-production (hog raising and poultry) industry in Cebu. Although the main operation is based in Bantayan Island (situated in the northernmost tip of Cebu Province), the Tayud Farm caters to the small and medium retailers of the municipality and the city.

As one of the wholesale buyers of eggs in Bantayan, Wellisa Farms trades on an average of over 2 million eggs per week which are transported from the island of Bantayan to Cebu. These eggs are transported in egg-trays made of paper pulp compared to the plastic trays being used in other parts of the country. The project is being nominated for the category “Renewable Energy for Non-power Application ” to demonstrate to the hog raising industry that tapping the waste can provide the energy revenue streams for the project. The project demonstrates a clear example of environmental and economic sustainability.


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Biogas Digester System

Biogas digester system The Biogas Digester System installed at Wellisa Farm is the fixed-dome type Chinese model digester. This design was taken from the Biogas Research and Training Center (BRTC), in Chengdu, PROC and was introduced and popularized by University

of San Carlos - Affiliated Nonconventional Energy Center (USCANEC) in the provinces of Cebu and Bohol. The system consists of four (4) concrete digesters of 100.0 cu.m. each, batch fed with an average retention time (RT) of 14 days per digester.

Settling Pond System A settling pond is installed after the outlet portion of the digesters to settle suspended solids regularly discharged where it is collected and dried for fertilizer use. On the last division of the settling pond, a water pump is installed to pump the water back to the piggery building for cleaning and flushing the pens.

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Settling pond system

Cleaning of pens using effluent


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Gas Collection System Each digester produces an average of 250-280 cu.m. of gas per day on pig manure alone. However, However, when chicken dung (fresh) was added into the feed material, the digesters were able to generate 300-350 cu.m. of gas per digester (1.0-1.5 cu.m. per digester volume) for a total of 1,200 to 1,400 cu.m. daily gas production. Since gas is generated on an hourly basis, biogas coming from the digester is piped and stored in gas collectors. In the farm, four (4) 30.0 cu.m. cylindrical steel gas collectors are placed over a cylindrical concrete water tank to ensure a steady supply of gas for use in the farm. As gas is being utilized and consumed, the tanks lower itself to the water seal tank and rises to its maximum level level and height as it is being

refilled. This type of gas collecting increases increases gas pressure by as much as 8kpa which is the working pressure for most gas fueled equipment.

Gas collection system

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Fertilizer System Most of the manpower assigned in the facility are concentrated concentrated in the scooping and drying of digested sludge which Workers assigned in the sludge c ollection in itself is an enterprise. Workers

get additional compensation of P4.00 for every sack of dried sludge they collect everyday. everyday. On the average average 20-25 sacks (40.0 kg) are collected and and dried per day. day. Dried sludge is then then mixed with processed chicken dung to balance the potassium and phosphorus requirement requirement (chicken (chicken dung is high in nitrogen nitrogen but low in K, P) and bagged. The organic fertilizer, fertilizer, under the brand name DURABLOOM, is commercially sold at an average of P200.00

per sack and now getting its its share of the market. At present, Wellisa Farm Tayud disposes an average of 20,000 bags per month in the Visayas Region alone.

A worker making organic fertilizer


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Pulp Moulding System The pulp molding system used a Silfurton machine that was procured by Wellisa Farms to support its demand for eggtrays to deliver eggs from Bantayan to Cebu. The system produces

an average of 20,000 pieces of paper pulp egg-trays per day. Most of this is consumed by Wellisa Farms. However, the project has reduced the dependency on egg-trays bought commercially at a price of Php 3.00 per piece and has reduced the cost per tray by almost 50%.

Egg-tray processing

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Use of Resources (including Power and Energy) The system resource consumption is summarized as: Biogas Digester and Farm Operations:

Electric Consumption : 30kw Digester Volume : 4x100 cubic meter Feeding material : 10 cubic meter of chicken dung and pig manure Gas Production : 1000 cubic meter per day Heating Value : 5500 kcal/cubic meter Recycled water for washing of pigs : 20,000 liters per day Paper Pulp Molding Machine:

Electric Consumption : 75kw Thermal Consumption: 600 liters of diesel or 1000 cubic meter of biogas Waste paper consumption: 2000 kg per day The total electric consumption of around 125kw (peak) is being evaluated to be generated using a biogas engine or other appropriate technology (using biogas) to eliminate the dependency

on the grid power. Government financial intervention is being considered for this project. As there is no envisioned shortage of gas from the waste stream (as supported by the operations for the past two years) this option is not considered. The maintenance of the biogas digester system is done in batches and does not affect the continuous operations of the system. There is also no change in the supply conditions for recyc led

newsprint which ensures timely delivery and stable costs.


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Environmental Impact The project aims to mitigate and enhance the following environmental impacts: Thermal Energy , the biggest environmental impact perhaps is the fuel switch from diesel to biogas. Prior to the development of the biogas system the thermal consumption for the paper pulp molding machine was around 600 liters of diesel fuel each day. This has been replaced by 1000 cubic meter of biogas. This also saves the daily logistics problems of transporting the diesel and refueling activities. The annual saving on diesel fuel is estimated at 1200 barrels or 200 liters. Water Pollution: Most pig farms as well as chicken farms

all over the world are confronted with the issue of meeting compliance standards for waste water discharge. All over the Philippines this problem is evidenced by the water quality within the river systems in major hog raising municipalities. Wellisa Farms, Tayud has demostrated that operations of a piggery can mitigate and manage the water polutions concerns if appropriate waste management systems are installed and maintained. Air Pollution: The multi-stakeholder approach involving

the local community and the Department of Environment and Natural Resources will attest to the improvement in the air quality

at Wellisa Farms, Tayud. The operations are free of the odor that is common in most piggery operations. Land Pollution: The use of settling ponds and the solid

separation for organic fertilizer has mitigated the land pollution that would be caused by lagoons which is the common practice in the industry.

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Also the application of organic fertilizer will replace the usage of chemical fertilizers that pollute the land and water over

a period of time. An average of 600 bags (40kgs each) of organic fertilizer is manufactured per month. Also the use of paper egg-trays as compared to plastic egg trays. Water Recycling: The project recycles on an average

about 20,000 liters of water each day. The system is almost a closed loop with very little water being pumped from the groundwater on a daily basis. Thus the scarce groundwater resource at Tayud is available for other users within the area. Paper Recycling: The project recycles on an average of

2000 kgs of used newspapers, cartons and other paper materials that are purchased from recyclers. This amounts to an annual recycling of 720 tons of paper.

Contribution to the Local Economy The successful operation of the project provides livelihood

for the 30 laborers who are also encouraged to make additional income through the production of organic fertilizer. Most of the manpower assigned in the sludge collection get an additional compensation for every sack of dried sludge they collect everyday. The success of the project has encouraged the owners to venture into much larger project involving paper pulp molding using biogas.

This will certainly put Cebu on the global map as a manufacturer of high quality, low priced paper pulp products. The outcome of such project will certainly have an economic impact not only on a local level but also on a regional level. Source: 2006 Green-E Awards Application. Category-Renewable Energy for Non-Power Application. Nominated by Solution Using Renewable Energy Inc. (SURE).


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Appendix C

Biogas Experts/Contractors/ Suppliers in the Philippines

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Cont...

Source: Technology Validation of Bio gas Technology an d Its Utilization in the Philippines: Terminal Report, CvSU-ANEC.


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Biogas Book 111711

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