NITIE, Mumbai
Moving Bed Biofilm Process An Innovation in Wastewater Treatment
Anant Maheshwari PGDISEM Class of 2011
CONTENT
INTRODUCTION BIOLOGICAL TREATMENT PROCESSES Purpose Principle Types BIOFILMS Advantages of Biofilm Processes Biofilm Systems in use MOVING BED BIOFILM PROCESS Principle Applications Process Design & Engineering Advantages BIOFILM CARRIERS Characteristics of Biofilm Carriers CASE STUDY Case of AstraZeneca, Sweden Case of ITC Ltd., PSPD Div., Andhra Pradesh REFERENCES
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INTRODUCTION Biological Treatment Process: Purpose: The idea behind all Biological methods of wastewater treatment is to introduce contact with bacteria (cells), which feed on the organic materials in the wastewater. Biological treatment processes are based on the activity of microorganisms and the main objectives are: Transform dissolved and particulate biodegradable constituents into acceptable end products. Transform or remove nutrients as N and P. Remove or reduce concentration of organic or inorganic compounds.
Principle: Microorganisms eat the organic material present pre sent in the wastewater. Through their metabolism, the organic material is transformed into cellular mass, which is no longer in solution but can be precipitated at the bottom of a settling tank or retained as slime on solid surfaces or vegetation in the system. The water exiting the system is then much clearer than it entered it.
Types: Suspended Growth Process: The microorganisms responsible for the treatment are maintained in the suspended state. It is commonly known as Activated Sludge process. It consists in a set of two basins. In the first, air is pumped through perforated pipes at the bottom of the basin. This provides oxygen form of air to the water and creates highly turbulent conditions that favor intimate contact between cells, the organic material in the water and oxygen. The second basin is a settling tank, where water flow is made to be very quiet so that the cellular ce llular material may be removed by gravitational settling.
Schematic View of Suspended Growth Process
Activated Growth Process: The microorganisms responsible for the treatment are attached to an inert packing material. A very common example of this process is Trickling T rickling Filter. It consists in a bed of fist-size rocks over ove r which the wastewater is gently sprayed by a rotating arm. Slime (fungi, algae) develops on the rock surface, growing by intercepting i ntercepting organic material from the water as it trickles down.
Schematic View of Attached Growth Process
Biofilm: A biofilm is a structured community of bacterial and other microbial cells enclosed in a polymeric matrix and adhered on an inert or living surface. Biofilms consists of three components: Microorganisms Extracellular Polymeric Substances (EPS) Surface
Advantages of Biofilm Processes: Higher process productivity (loading rates) Higher biomass holdup Higher mean cell residence time No need for biomass recirculation reci rculation Creates suitable environment for each type of bacteria Sustains toxic loads
Biofilm Systems in use: Rotating Biological Contactor (RBC) Trickling filter Fixed media submerged biofilters Granular media biofilters Moving Bed Biofilm Reactor (MBBR) Fluidized bed reactors
Trickling filter
Moving Bed Biofilm Reactor
Rotating Biological Contactor (RBC)
Fluidized bed reactors
MOVING BED BIOFILM PROCESS Principle: The basic principle of the moving bed process is the growth of the biomass on plastic supports that move in the biological reactor via agitation generated by aeration systems (aerobic reactors) or by mechanical systems (in anoxic or anaerobic reactors). The supports are made from plastic with a density close to 1 g/cm 3 letting them move easily in the reactor even when the capacity reaches 70%. The moving bed processes come from the current trend in waste water treatment, from the use of systems that offer an increased specific surface in the reactor for the growth of the biomass, achieving significant reductions in the biological reactor volume. Suspension within the reactor is kept in continuous movement by either aeration (in aerobic reactors) or mechanical mixers (in anaerobic and anoxic reactors).
Aerobic Aerobi c Reactor with Aeration System
Anaerobic Reactor with Mechanical Stirrer
Initially fixed bed systems were used, however it was discovered that this type of process show a series of operational inconveniences such as the blocking of the bed because of the excessive growth of the biomass, this makes periodical cleaning obligatory. These drawbacks have caused the need for the creation of simple biofilm processes that eliminate them and that ease their operation; these are the moving bed processes. p rocesses.
Applications: This type of process can be applied both to treatment plants for the biodegradation of organic material as well as for installations with nutrient elimination, in urban and industrial wastewaters. Another application is the use of this technology in the redesign of current activated sludge processes, which only treat organic material, to expand them and include simple nitrogen elimination without the need to construct new biological reactors.
With respect to the aeration system is via a grid of perforated stainless steel tubes that avoid problems of efficiency loss, diffuser replacement, etc. MBBR is widely used in all kinds of industries across the globe for various purposes. Following industries are using MBBR as the biological treatment unit in their treatment plant: Municipal Wastewater Food Processing Industry Pulp & Paper Industry Pharmaceutical Industry Petroleum / Chemical Industry Electronics Fish Farming
Schematic diagram of MBBR system
Process Design & Engineering: Major components of the system are: a. Media b. Stainless Steel c. Aeration System d. Stainless Steel e. Sieve Assemblies f. Tank g. Blowers h. Instrumentation & Controls Certain other features of the system are as follows:
Media Retention: A stainless steel wedge wire sieve is used to retain the media. Aeration Grid: A stainless steel grid mounted at the bottom. The grid is connected to high efficiency blowers which produces a medium bubble which provides the necessary mixing. Operated at a DO concentration of 5 - 7 mg/l. Retention times in the MBBR tank are in the order of 15 to 30 minutes. minutes . Followed by an efficient efficient particle separation to remove remove particulate matter. Settling is enhanced by Coagulation (retention time 15-20 mins.) followed by separation by floatation, cloth or filtration.
Aerobic reactor with aeration system and vertically mounted cylindricalbar sieves
Anoxic reactor with horizontally shaft mounted mixers and rectangular mesh sieves
Advantages compared to conventional biological processes: In general, the main advantages shown by the moving bed process p rocess compared to conventional biological processes are: A reduction in the volume of the biological reactor because it uses a support or carrier that gives a high specific surface. They are very flexible processes since they are based on the percentage of plastic support used in the reactor, it is recommended that it is not greater than 70%, the surface can be modified and as a consequence the efficiency of the process.
It does not require reactor biomass recirculation – This gives rise to the fact that the biomass does not depend on the final separation of the sludge and as a consequence typical problems found in conventional activated sludge processes related to the sedimentation properties of the sludge (filamentous bulking, etc.). e tc.). The operation and control is simple for this type of processes.- On the one hand the process avoids blockage problems and consequently regular cleaning periods, in addition it is not necessary to control the sludge purging since the system keeps the biomass in the reactor until it comes off the support. It allows the generation of a characteristic biomass for each type of reactor (aerobic, anoxic or anaerobic) bringing about the creation of a biofilm with a high level of activity. Experimentally it has been confirmed that the levels of nitrification and denitrification in this type of processes are greater than those obtained in conventional processes.
Operational stability and maintenance: The Moving Bed Biofilm process requires no sludge recirculation and has a robust operational design regarding factors such as temporary limitation of nutrients, toxicity, as well as pH- and temperatures shocks. These factors may temporarily reduce the biological capacity of the biofilm system, but will not significantly affect the biomass in the reactor. Due to the continuous movement and pre-treatment by means of screening the MBB process is generally not prone to clogging. However, in upgrading existing treatment plants that operate without primary settling and rather large screen sizes, the carrier material should be chosen correspondingly to prevent clogging.
Biofilm Carriers: The core of the process is the biofilm carrier elements on which attached growth of microorganisms takes place. The elements are made from polyethylene with a density slightly lower than water. The biofilm carrier elements are kept suspended in the water by air from the diffusors in aerobic reactors and by means of propeller mixers in anaerobic and anoxic reactors. The carrier elements are retained by means of suitably sized sieves or plates. The original KMB carrier elements are about 7 mm long and 10 mm in diameter and designed to provide a large protected surface for the biofilm and optimal conditions for the bacteria culture when the elements are circulated in the water. The carrier elements are wheel shaped with longitudinal fins at the outside. They are made of polyethylene having a density of 0.96 g/cm 3, which allow easy movement of the carrier material in the completely mixed tanks. The carrier material is retained by perforated plates (usually 5x25 mm).
The reactors are normally filled up to 67% of their volume with biofilm carrier elements corresponding to an effective biofilm area of 250 to 350m 2/m3 water volume, depending on the carrier shape and size used. Due to the shape of the carrier elements, only 12% of the water is displaced.
Moving bed plastic media
Bacteria in plastic media
Characteristics of The Anox Kaldnes Biofilm Carriers
CASE STUDY #1
Pharmaceuticals Company Södertälje, Sweden
Company Profile: - A world leading pharmaceutical pharmaceutical company with a world-class world-class biologics capability. - Active in over 100 countries with a growing presence in important emerging markets including China; corporate office in London, UK; and major R&D sites in Sweden, the UK and the US. - Sales in 2008 totalled totalled $31.6 billion. billion. - 26 manufacturing sites in 18 countries .
Background: In 1992, AstraZeneca approached AnoxKaldnes in order to obtain a state of the art solution for a new treatment plant. The wastewater from the pharmaceutical production was highly toxic and in addition contained many difficult-to-degrade organic compounds. The recipient was the very sensitive Lake Mälaren, which surrounds several cities including the capital Stockholm. To be able to discharge the wastewater into Lake Mälaren it had to be totally detoxified and at thesame time at least 95% of the organic content had to be removed. Solution: Several activated sludge processes were initially unsuccessfully tested. The main problem was that the wastewater was toxic not only for animals and plants but also for the bacteria used in biological treatment processes. An R & D project was then launched basedon the newly developed Natrix™ biological process. It was demonstrated that only certain microfungi could resist and break down the toxic compounds. The Natrix™ technology is different in the carrier it uses. The patented Natrix™ carrier is normally from 31 to 50 mm in length and from 31 to 60 mm in diameter. The carriers are injection moulded high density polyethylene/calcium carbonate. The filling volume is typically 30 to 50% of the reactor volume. The Natrix™ process can treat wastewater with total suspended solids contents of 1000 to 2000 mg/l, up to this moment the process has been nearly exclusively used in industrial applications. A tailor-made treatment process in six stages was develope d. In the first three MBBR reactors fungal growth is promoted by lowering pH to 4. In the following three stages, when the wastewater was detoxified, pH is adjusted to 7 to promote bacteria that take c are of the residual organic compounds.
Dimensioning: The flow is approx. 1800 m3/d. Incoming TOC averaging 440 kg/d but varies considerably because of batch-wise production. The hydraulic retention time in each reactor is 3-4 h. The biological treatment process is complemented with chemical phosphorous ph osphorous precipitation and polishing with activated carbon and a sand filter to takecare of any residual toxicity and suspended solids, respectively .
Results: The treatment plant has been operational since 1997 and the treatment results have been superior. In addition, the built-in tolerance to peak loads and toxicity in the Natrix™ biological process has provided a very stable operation that could not have been obtained with conventional treatment processes. The treated wastewater is totally detoxifyed by the action of the microfungi that also takes care of 80% of TOC. The bacterial communities in the following reactors remove additional organic substances so that the overall TOC removal is 97%. Approximately 80% of incoming nitrogen is removed (far more than the discharge limit) and Phosphorous removal is 99%. During the years, environmental studies of the discharge point have shown that the recipient has not received any residual toxicity from the treatment process and that the amounts of nitrogen, phosphorous, phosphorous, COD and suspended solids have decreased dec reased in the area.
CASE STUDY #2
ITC Limited Paperboards & Specialty Papers Division Bhadrachalam, Andhra Pradesh
Company Profile: PSPD, a Division of ITC Ltd, is India’s largest and most technology advanced Pulp & Paper
business paperboard co. of capacity 4.0 Unit Bhadrachalam is I ndia’s largest single location integrated paperboard lac TPA Paper and Paper Board
30% Market share in 2008-09 : growing to 45% by 2009-10 in paperboards segment Usage of 90,000 TPA Recycled fiber
Treatment Facilities at site: Mechanical pre-treatment o Bar screen primary clarifier o
Biological treatment Activated sludge o MBBR o
Post treatment Clarifier (Mechanical) o
ETP Flow sheet
Process Design: Number of reactors : 2 Reactor dimensions: 21.3 m x 21.2 m x 8 m (WxLxH) Water depth : 7 m Reactor volume : 3200 m3 each Media type : Biofilm-Chip P Amount of media : 320 m 3 in each reactor Void volume : 80% MBBR Inlet Conditions: Parameter
Unit
Design
Flow
m3/d
44,000
pH
std. unit
6-8
0
Temperature
C
Max 40
TSS
mg/l
<120
COD
mg/l
720
Results: Parameter
Unit
MBBR inlet
MBBR outlet
COD
mg/l
1120
672
BOD5
mg/l
450
60
Achieved COD reduction by 40 % at MBBR outlet Achieved BOD5 reduction by 87%
REFERENCES
http://www.sciencedirect.com http://www.greenbusinesscentre.org http://www.veoliawaterst.com/processes/lib//pres/DB16yRyQ59FJ5S17v5bWSb3 v.pdf http://www.accaglobalgroup.com/EEC_HOW_SYSTEMS_WORKS.pdf http://www.sabesp.com.br/sabesp/filesmng.nsf/570F9FE72CBC3BB2832574F2005 81095/$File/mbbr_chandler_johnson.pdf http://www.scipub.org/fulltext/ajes/ajes46675-682.pdf http://www.xauat.edu.cn/FUWWS-XIAN2005/keynote-pdf/Hallvard.pdf www.anoxkaldnes.com http://www.water.siemens.complications/wastewater_treatment/Pages/Granado r_Juice.aspx http://www.veoliawaterst.com/processes/lib//pres/DADC813X5P3s5ERP572ZV4L b.pdf
