INDUSTRY DEFINED PROJECT ON “EFFICIENT DEWATERING OF SLUDGE” at “Naroda Enviro Project Limited” Submitted by DEEP SHAH (120170105011) JANIT PATEL (120170105013) APURVA PATEL (120170105003) JEET PATEL (120170105017) NIRAJ CHAUDHARY (120170105047) B.E. (Chemical), 7th Semester In fulfilment for the award of the degree of Bachelor of Engineering In Chemical Engineering
Chemical Engineering Department Vishwakarma Government Engineering College, Gandhinagar Gujarat Technological University, Ahmedabad October, 2015
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GOVERNMENT ENGINEERING COLLEGE GANDHINAGAR CHEMICAL ENGINEERING DEPARTMENT (Department of Technical Education, Gujarat State, Gandhinagar) Nr. Visat Three Roads, Visat-Gandhinagar Road, Chandkheda, Gandhinagar – 382424.
Date:- 16/10/2015
CERTIFICATE This is to certify that the project of “Efficient Dewatering of Sludge” been carried out by SHAH DEEP, PATEL JANIT, PATEL APURVA, PATEL JEET, CHAUDHARY NIRAJ under my guidance in the fulfilment of the degree of bachelor of engineering in chemical department of B.E final year of Gujarat Technological University, Ahmedabad during academic year 2015-2016.
__________________________
_________________________
Prof. D.R.GANDHI
Prof. N.M.PATEL
Project Guide
Head of the department
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ACKNOWLEDGEMENT Each and every person in this world has to depend on other for one or other help. No person can accomplish this task without the help of others. Similarly during our project work we directly and indirectly received help from some personalities. We are greatly indebted to them for their help. First of all we would like to thank Mr. Satish Patel (Plant Incharge), NEPL then our guide Prof. Dolly R. Gandhi for her excellent help by providing internet and required book facility in college, For her ever-tiring excellent guidance. This helped us a lot during work. Not only her guidance but also her consistent encouragement inspired us a lot to complete this project in a successfully and satisfactory manner. And also we are very thank full to Prof. N.M. PATEL (Head of department) for their administrative support. We take this opportunity to thank NEPL staff who have taken great pain by fulfilling my requirements whenever we needed help. Last but not least we thank the almighty for giving us excellent mental and physical strength for completing the project work successfully. . DEEP SHAH JANIT PATEL APURVA PATEL JEET PATEL NIRAJ CHAUDHARY
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ABSTRACT Chemical industry being a vital sector of nation along with tons of useful chemicals also produces large amount of waste, which needs to be treated. ETP are used for this purpose. However, they face challenges in making the industrial sludge completely dewatered as well as its disposal by land filling, incineration, dumping etc. If the sludge is not properly disposed may result in mere shifting of pollutant from waste stream to final disposal site, where they may again become free to contaminate the environment. ‘Sludge dewatering’ is, as the name clearly implies, removing water from sludge. Sludge dewatering is typically the final step for industrial waste water treatment processes and plants. After waste water treatment the sludge remaining is very high in water content that can be reclaimed through sludge dewatering. There are many processes like physical process, chemical process, and biochemical process. It is required to remove the solid content from the sludge. After removing the solid, treated water can be used for agriculture use and reducing the environmental issues. So, we will work on “EFFICIENT DEWATERING OF SLUDGE”, which will ensure maximum recovery of liquid as water from sludge to isolate the solids and then investigate composition of solids for its further extraction of metals, if possible. This will contribute towards reduction in environmental contamination and high recovery of water.
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INDEX CHP.NO.
CHAPTER
PAGE NO.
1.
COMPANY PROFILE
1
2.
INTRODUCTION TO SLUDGE
3
2.1
What is sludge?
4
2.2
Sludge characterization
4
2.3
Origin of sludge
4
2.4
Type of sludge
4
3.
LITERATURE SURVAY
6
3.1
Introduction
7
3.2
Concept of CETP
7
3.3
Advantages and limitations of CETP
8
3.4
Design criteria for CETP
8
3.5
Process and design parameters for CETP
8
3.6
Method
9
3.7
Design parameters
9
4.
11
4.1
NEPL EFFLUENT TREATMENT PLANT Block diagram
4.2
Process flow diagram
13
4.3
Process description
14
5.
PROBLEM IDENTIFICATION & CONCLUSION REFERENCES
20
12
24
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LIST OF TABLES Table no. 1 2
NAME OF TABLE Typical design parameters for activated sludge process Typical minimum SRT range for activated sludge treatment
PAGE NO. 10 10
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CHAPTER:-1 COMPANY PROFILE
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COMPANY PROFILE Naroda Enviro Projects Ltd. is a company registered under section 25 of the companies Act, 1956 and working on "No Profit No loss" basis. The company is established in 1995, pursuant to landmark judgement given by Hon. High court of Gujarat under SCA No. 770 of 1995. The company is working as a Nodal agency between Industrial Units and various Government agencies. The company has main two projects : (1) The common Effluent Treatment plant (CEPT), which is giving services to the polluting industries of Naroda GIDC Estate.
Aerobic treatment Anaerobic treatment Multi-effect Evaporator (ME)
(2) Treatment, storage and disposal facilities (TSDF), giving services to industries of Gujarat to dispose their hazardous waste in sufficient manner. Location of company: Naroda Enviro Projects Ltd. (NEPL) Plot No. 512-515, Phase 2 Naroda, Ahmedabad
dhffkfkf COMMON EFFLUENT
MULTI-EFFECT
TREATMENT PLANT
EVAPORATOR (ME)
EFFLUENT
ANAEROBIC
SOLID WASTE
TREATMENT
MANAGEMENT
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CHAPTER:-2 INTRODUCTION TO SLUDGE
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2.1 What is the sludge? Semi-liquid residue from industrial processes and treatment of sewage and wastewater.
2.2 Sludge characterization: There are several types of sludge that have specific characteristics that will influence: The choice in conditioning chemical (cationic flocculants, ferric chloride, lime…) The choice in the dewatering equipment to be used (filtration, centrifuge…) These choices will also depend on the final use of the sludge (incineration, agricultural spreading)
2.3 Origin of the sludge: During the course of the water treatment, products coming from the pollution are extracted while the treated water is released in the environment. Among these products coming from the pollution one can distinguish: Particles that decant naturally or that come from the physio-chemical treatment Excess micro-organisms coming from dissolved organic matter treatment Mineral matter that is non-biodegradable All these products are suspended in more or less concentrated forms and the resulting liquid is called sludge.
2.4 Different Types of sludge:1. Primary sludge: Primary sludge comes from the settling process. It is therefore made of easily decantable suspended particles: large and/or dense particles. It has a low level of Volatile Solids content (VS around 55% to 60%) and its dewatering ability is excellent. It is also very easy to concentrate this type of sludge with a static thickening step just before dewatering. The drawback is that this sludge ferments very easily.
2. Biological sludge: Biological sludge comes from the biological treatment of the wastewater. It is made of a mixture of microorganisms. These microorganisms, mainly bacteria, amalgamate in bacterial flocs through the 1 Synthesis of Exo-polymers. A simple decantation in the clarifier will easily separate the bacterial flocs from the treated water. Only part of this settled sludge is sent to dewatering: the excess biological sludge; part of it is re-circulated to maintain the bacterial population in the reactor. To simplify, we will not differentiate between the different qualities of biological sludge (prolonged aeration, low charge, high charge…); their main properties are: 4|Page
● A high Volatile Solids content: VS around 70% to 80%. ● A low dry solids content: 7 g/l to 10 g/l. It is often necessary to introduce a . dynamic thickening step by flotation or gravity belt. ● The dewatering ability is medium. It depends partially on the VS. The higher the VS the harder it is to extract the water from the sludge.
3. Mixed Sludge: Mixed sludge is a blend of primary and biological sledges. The blending ratio is often as follow:
35% to 45% of primary sludge 65% to 55% of biological sludge.
This blending will permit an easier dewatering as the intrinsic properties of the sludge are other between two types.
4. Digested sludge: Digested sludge comes from a biological stabilizing step in the process called Digestion, this stabilization is performed on biological or mixed sludge. It can be under different temperatures (Mesophilic or Thermophilic) and with or without the presence of oxygen(aerobic or anaerobic). following this stabilization step the
A lower volatile solids content: VS around 50%. A mineralisation of the sludge occurs during digestion A dry solids content around 20 g/l to 40 g/l. A good dewatering ability.
5. Physio-chemical sludge: This type of sludge is the result of physio-chemical treatment of the waste water. It is composed of flocs produced by the chemical treatment(coagulants and/or flocculants).The characteristics of this sludge is the direct result of the chemicals used (mineral or organic coagulants) and of course of the pollutants in the water.
6. Mineral sludge: This name is given to sludge produced during mineral processes such as quarries or mining beneficiation processes. Their nature is essentially mineral particles of various sizes (including clays). They have a very good aptitude to settle by gravity and very high concentrations are frequently obtained.
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CHAPTER:-3 LITERATURE SURVEY
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3.1 INTRODUCTION:Huge rise in the number of small-scale industries can be seen in any Indian city due to easily finance available from market and increasing the demand of goods. Is generally observed that, either due to their economics of scale coupled with their unplanned growth and dearth of affordable and cost effective treatment technology, efforts by small scale units in achieving the environmental compliance has not been effective. Under these constraints, setting up of individual full-fledged treatment device is no longer feasible. Hence the desirable option is of the shared or combined treatment, wherein, managerial and operational aspects are collectively addressed and cost of treatment, becomes affordable as enunciated in the scheme of the common effluent treatment plant, which are proving to be a boon especially for all industries.
3.2 CONCEPT OF COMMON EFFLUENT TREATMENT PLANT (CETP): CETP not only helps the industries in easier control of pollution, but also acts as step towards cleaner environment and service to the society at large. Small scale industries, by their very nature of job cannot benefit much from economics of scale and therefore the burden of installing pollution control equipments, falls heavy on them. Realizing this practical problem, under policy statement for abatement of pollution the Govt. felt to extend the scheme for promoting combined facilities for treatment of treatment of effluent and management of solid waste for clusters of small scale industrial units and also to provide technical support to them. The combined treatment provides a better economical option because of the equalization and neutralization taking place in the CETP. Other important issues for merit for common treatment include scarcity of land at the industry’s level and a comparatively easier availability of professional and trained staff for the operation of CEPT, which can otherwise be difficult, at the individual level. The concept of common treatment, based on feasibility, should be part of the new industrial estates as essential component of infrastructure. In fact, the location of industries should always be such that units with compatible nature of activity are located in a cluster which in turn can facilitate in providing common treatment.
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3.3 ADVANTAGES OF COMMON EFFLUENT TREATMENT PLANT: Saving capital and operation cost of treatment plant. Combined treatment is always cheaper than small scattered treatment plants. Availability of land, which is difficult to be ensured by all individual units in the event, they go for individual treatment plant. Contribution of nutrients and diluting potential makes the complex industrial waste more amenable to degradation. The neutralization and equalization heterogeneous waste makes make its treatment techno economically viable. Professional and trained staff can be made available for operation of CETP, which is not possible in case of individual plant. Disposal of treatment wastewater & sludge becomes more organized. Reduced burden on the various regularity authorities & ensure pollution control requirement.
3.4 LIMITATION OF CETP: There is uncertainty of toxicant discharge by various industries so there is also uncertainty prevailing discharge of BOD< COD and suspended solid from different industry. These uncertainties will seriously effect on the performance of the plant.
3.5 DESIGN CRITERIA FOR CETP:
Inventory of industries Qualitative and quantitative characterization of wastewater from industries Classification of industries based on wastewater generation Classification of wastewater based on bio-degradability Site-specific, effective and easy to maintain design of conveyance system Bench scale and pilot scale treatability study Segregation of wastewater Pre-treatment of wastewater Assessment of appropriate treatment technology Waste minimization and resource recovery Disposal mechanism of treated technology Estimation of treatment cost Cost benefit analysis Selection of best suited cost sharing pattern Stress on cleaner technologies.
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3.6 Method: Activated sludge process is a complex dynamic process and stimulation of such system must necessarily account for a large number of reactions between a large number of components. If there is a load for BOD, COD, TDS is increase on the activated sludge process then from the modelling and stimulation of the process we can predict that how the efficiency of the progress get affected. If the total wastewater flow rate on the plant increase or decrease then we can predict that how the efficiency of the process get affected. If there is a load of volatile organic compound increase on the process then we can predict that how the performance of the plant get affected. The growth rate of bacteria in the tank can be predicted by modelling and stimulation of activated sludge process. Activated sludge process consists of two units- the aeration tank and the secondary clarifier. From the bottom of the secondary clarifier, Settled and concentrated sludge is returned back to the aeration tank to maintain the mixed liquor suspended solids (MLSS) at desirable level. Excess sludge thickener to keep the system operating at a controlled sludge age (mean cell residence time, MCRT or sludge retention time, SRT). Activated sludge process is the most widely used secondary treatment process for treating both municipal and industrial wastewaters. Within the activated sludge process, the biological reactor, aeration tank, plays a more important role and has been the focus of much research, which is also the focus of the investigation.
3.7 Design parameters for activated sludge process:
mean cell residence time solids in aeration tank sludge volume index food to micro-organism ratio dissolved oxygen concentration organic loading biological view nutrient requirement
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Typical design parameters for activated sludge process: Process components
Typical values from literature
Aeration basin Depth(m) Width (m) Mean cell residence time(day)
5-8 7-12 5-15
MLSS(mg/l)
1500-4000
SVI(mg/l)
40-150
F/M(kg BOD/kg MLVSS d)
0.2-0.4
RAs rate (% influent rate)
30-100
Organic loading rate (kg BOD/1000 m3d)
335-1000
Typical minimum SRT range for activated treatment: Treatment Removal of soluble BOD in domestic wastewater
SRT range in days 1-2
Conversion of particulates organic in domestic wastewater
2-4
Complete nitrification
3-18
Biological phosphorous removal
2-4
Stabilization of activated sludge
20-40
Degradation of xenobiotic compound
5-50
Develop flocculent biomass for treating industrial wastewater
3-5
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CHAPTER:-4 NEPL EFFLUENT TREATMENT PLANT
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4.1 BLOCK DIAGRAM:-
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4.2 FLOW DIAGRAM:-
(1) — indicates Chemical Sludge (2) — indicates Biological Sludge (3) — indicates Treated Water
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4.3 PROCESS DESCRIPTION: The CETP Naroda is using conventional process for the treatment of wastewater. Selection of this process is being done by doing the treatability study of wastewater. Selection of process is being done by analyzing sample of all the members on the basis of the mixed sample of all members. The CETP plant is located in Naroda G.I.D.C. The process flow diagram of CETP Naroda is shown in above figure. The effluent from the member industries comes to the screen chamber which the first of the preliminary treatment of the effluent. The principle role of the screening is to remove coarse material from the flow stream. The effluent from screening chamber goes to the collection sump before subjecting it further treatment. From the collection sump the effluent goes to oil and grease separator. Its main function is to remove lighter partials which have escaped through the screens, oil and grease which are lighter than water. Effluent from oil and grease separator is taken into equalization tank. The purpose of the equalization tank is to provide homogenized effluent for further treatment. Because of the fill and draw type of mode, part of the chemical treatment like neutralization can also be carried out in the equalization tank. The effluent from the equalization will be pumped to the flash mixer. The flash mixer is provided with turbine type impeller. The various coagulating/flocculating agent and polyelectrolyte is added in the flash mixer through the metering pumps and rapid mixing is provided so as to make homogenous effluent for the effective flocculation. The effluent from the flash mixer will go to the center feed clariflocculator by gravity. The clariflocculator will perform for different functions. The central part is provided with two tubes settler and the flash mixer wastewater enter the clariflocculator from the central column. The outer portion of the clariflocculator provided quite large zone for settlement and separation of the flocs. The overflow of the clariflocculator will be taken to the aeration tank for the biological treatment. In the aeration the reduction of BOD take place by microorganism. In the aeration tank dissolved oxygen will be maintain through diffused aeration. The biomass will be developed acclimatized to suit quality of the primary treated effluent. Once the biomass is developed then it will be maintained by, 1) Providing diffused air from four different root blowers. 2) Recirculation of the settled sludge from the secondary clarifiers. 3) Addition of required nutrition like Urea and DAP so as to have healthy growth of acclimatized biomass.
Biomass will degrade the dissolved organic content of the incoming of the effluent through the metabolic activity and convert them to carbon dioxide and water. This degradation of the dissolved organic matter will reduce the COD and BOD of the effluent. 14 | P a g e
The overflow of the aeration tank will be taken to the secondary clarifier. The biomass will be settled and the clear effluent from the clarifier will do to the treated water dump. For removal of the settled sludge from the bottom will be pumped backed to the respective aeration basin and the excess of the sludge will be taken to the sludge thickener. Primary sludge providing to collect the sludge from the clariflocculator. The primary sludge collected in the sumo will be taken to the sludge dewatering device. Thickener is provided to concentrate to biological sludge from the secondary clarifiers so that the quantity of the sludge with lesser quantity and higher concentration can be produced. The concentrated quantity of the sludge will require less area for sludge drying. The overflow of the thickener will be taken to the equalization tank whereas the sludge will be taken to the sludge drying beds. The combination of aeration tank and secondary clarifier is known as activated sludge process. The following stated variables are considered in activated sludge process: Growth rate of bacteria in aeration tank, 1) BOD removal 2) Nitrogen removal 3) Phenol removal 4) Dissolved oxygen concentration.
OPERATION & MAINTENANCE:1. SCREEN CHAMBER : The effluent of the member industries comes to the screening chamber which is the first stage of the preliminary treatment of the effluent. The size of the screen chamber is 1.0m × 1.0m × 1.0m. The screen chamber is provided with inclined bar screens consisting of 6mm thick MS plate placed at angle 45° and at a distance of 25mm c\c. The main function of the screen chamber is to remove larger floatable solids and allow the smooth pumping of the raw effluent. The screen chamber is also provided with a well having a ladder for the periodical cleaning and removal of the reject. After the removal of the larger floatable solids the effluent enters the collection sump by gravity. 2. COLLECTION TANK : Size of collection sump is 5.5m × 5.5m × 3.0m. The effluent is collected in the sump before subjecting it to further treatment. The walls of the collection sump are acid proof brick lined as an apprehended protective measure against the accidental discharge of acidic effluent. The effluent from the collection sump is pumped (15 Hp capacity). To the primary celery flocculator by self-priming pump having SS shaft and SS rotor. 15 | P a g e
3. FLASH MIXER : Rapid mixing is provided in the flash mixer so as to make homogenous effluent for effective flocculation. The effluent from the flash mixer will go to the Centre feed clariflocculator by gravity. 4. CLARIFLOCCULATOR: The effluent from the flash mixer will come to clariflocculator by gravity. The clariflocculator is a circular tank of the size 14.0 diameter with a depth of 3.0 m with circular flocculation zone of 3.0 m diameter at the center. The flocculator will perform two different functions: (1) The central part is provided with two steps of paddles type flocculator having 20 to 30 RPM. The slow moving of the paddles will form the flocs when the flash mixerwaste water enters the clariflocculator from the central column. (2) The outer portion of the clarifocculator provides quiet zone for settlement and separation of the flocs. The flocs free water will then overflow from the launder and will go to the aeration tank. The sludge settled at the bottom will be removed from the bottom by gravity to primary sludge sump. For effective removal of the sludge, a scrapper with a peripheral drive is provided. INFLUENT CHARACTERISTICS COD=3500-5000 mg/l BOD=1200-1800 mg/l SS=600-900 mg/l TDS=15000-20000 mg/l
EFFLUENT CHARACTERISTICS COD=800-1500 mg/l BOD=1200-1800 mg/l SS=100-150 mg/l TDS= 15000-20000 mg/l
5. PRIMARY SLUDGE SUMP: Primary sludge sump is provided to collect the sludge from the clariflocculator. The primary sludge collected in the sump will be taken to the sludge dewatering device i.e. the decanter. 6. SLUDGE DECANTER: Looking to the quality and quantity of the sludge and with a view to have flexibility in the operation of the system during monsoon; two type of sludge dewatering system have provided. They are;
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1) Sludge drying beds (4 in nos.) each of size 11.0m x 7.0 (for secondary sludge) 2) Decanter of Alpha level The clear filter will be taken back to the equalization tank whereas the sludge cake will be allowed to dry and then packed in HDPE bags and stored on impervious area. From these areas the dried sludge will be transported to the hazardous waste disposal site. 7. FILTER PRESS: A filter press is typically less costly to install than compared to rotary drum vacuum. A filter press is a solid liquid separation device using the principle of pressure feeding. The filter medium is provided in between the plates. A feeding pump is utilized to force the liquid through the medium leaving the solid trapped inside. The sludge from the decanter will pass through the filter and the water and solid sludge will be separated. The filter press is under construction. 8. EQUALISATION TANK 1 & 2: Three equalization tanks each of size of 24.0m x 12.0 x 3.5m have been provided. All the equalization will work independently through fill and draw system. The equalization tanks are provided with course air diffused system. The purpose of the equalization tank is to provide homogenized effluent for further treatment. Because of the fill and draw type of mode, part of the chemical treatment like neutralization tank can also be carried out in the equalization tank. The effluent from the equalization tank will be pumped tank will be pumped to the flash mixer. 9. OIL & GREASE TRAP: The size of the oil & grease trap is 14.0m x 3.5m x 2.5m. Its main function is to remove the lighter particles which have escaped through the screens and oil and grease which are lighter than water. The oil and grease trap is provided immediately after pumping the larger cross section area will help to reduce the velocity and in turn reduce the oil and grease. The baffles walls provided in oil and grease trap will help the oil to float. The oil scum accumulated on the surface of the water will be removed periodically through manual operation. The overflow of the oil and grease trap will go to the equalization tanks. 10. HOLDING TANK 1, 2 &3: The water is trapped in all the holding tanks one by one. The water from the equalization tank moves through the flash mixer and reaches holding tank-1 then after that reaches to tank-2 and tank-3. The uniform mixing is done in the holdings. 17 | P a g e
11. FLASH MIXER: The various coagulating/flocculating agent and polyelectrolyte is added in the flash mixer through the metering pumps and rapid mixing is provided so as to make homogeneous effluent for effective aeration. The effluent from the flash mixer will go to the flash channel from there it reaches to the tube settlers. 12. TUBE SETTLER 1 & 2: Tube settlers can be applied to new or existing clarifiers operated at 2 to 4 times the normal rate of clarifier. The coagulant is cut up to half. Care should be exercised by the contractor in unloading, transporting and placing tube modules. There are two tube settlers. Through tube settler-1, the water from the holding tank is carried to aeration tank and tube settler-2 carries from sewage industry. 13. AERATION TANK: The overflow of the clarifocculator will be taken to the aeration tank for the biological treatment. Two aeration tanks each of size 31.0 diameter and 5.6 m depth are provided. Four semi circle independent compartments are provided by providing partition wall dividing the circular aeration tank at the centre. By providing four compartments flexibility and effectiveness of the biological treatment will increase because anyone compartment can be taken for maintenance/ repairing without disturbing the functioning of the remaining eg In the aeration tank the dissolved oxygen will be maintained through diffused aeration. For diffused aeration disc type, membrane of Envirex- USA has been provided. The biomass will be developed acclimatized to suit the quality of the primary treated effluent. Once the biomass is developed then it will be maintained by(1) providing diffused air from four different root blowers.(2) recirculation of the settled sludge from the secondary clarifiers and (3) addition of required nutrition like urea and DAP so as to have healthy growth of acclimatized biomass. 14. SECONDARY CLARIFIER 1 & 2: Two centre feed secondary clarifier each of diameter 23.0 x 3.5 have been provided. The overflow of the aeration tank containing the biomass will be taken to the secondary clarifier through gravity. The biomass will be settled and the clear effluent from the clarifier will go to the treated water sump. For the removal of the settled sludge at the bottom rotating scraping mechanism of M/s voltas have been provided. The settled sludge from the bottom will be pumped backed to the respective aeration basin and the excess of the sludge will be taken to the sludge thickener.
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15. TREATED WATER SUMP: Treated water sump is a holding tank for the treated water, from where it can be pumped to the proposed Naroda-Odhav-Vatva-Narol drain line being constructed by Ahmedabad municipal corporation(AMC). Sufficient land area has been provided adjoining to the sump so as to accommodate tertiary treatment if any required. The size of the sump is 14.0m x 7.0m x 3.5m.
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CHAPTER – 5 PROBLEM IDENTIFICATION AND CONCLUSION
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Problem identification: The major problem that NEPL, naroda faces is the high cost of sludge disposal, since they are heavy in weight and disposal payment is on weight basis. After analyzing the entire process flow diagram, we found the following areas (marked with red circle) on which, we can work to produce more dewatered sludge and increase the efficiency of dewatering. The flow diagram is shown below :
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Following problems are identified:(1) (2) (3) (4)
Chemical dosing/pretreatment after the collection sump. Chemical pre-treatment before flash mixer. Inefficient flocculation before dewatering. Decanter (since it removes only 20% water).
So, we would like to work on, (a) “Efficient dewatering”, which reduces problem number (4). (b) “Chemical flocculation and treatment”, which reduces problem (1),(2), and (3) and also helps for the reduced energy requirement for (4).
Why we want to work on Dewatering of the sludge? The general objective of dewatering is to remove water there by reducing the sludge
volume. This produces a sludge which behaves as a solid and not as a liquid and reduces cost of subsequent treatment and disposal. In most cases, the percent solid content of a dewatered sludge is set by the requirements for disposal. This percent solids is subsequently higher than percent solids content of a thickened sludge. Most producers pay for sludge disposal by weight and water is heavy.So, if you remove as much water as possible, your dewatered sludge is lighter and this costs loss to dispose of your sludge and increase the number of reacting options. The water obtained is used for the purpose of washing and dilution in food grade industry. The sludge obtained being dewatered thus becomes compact and enhances the waste minimization. As the sludge is efficiently dewatered, toxins are removed to maximum level hence provides environmental protection.
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Conclusion: For the purpose of, “Chemical flocculation” and “Dewatering”, various physical and chemical method can be used. Chemical flocculation:(1) Pre-treatment with an chemical agent (2) Chemical dosing Dewatering:(1) (2) (3) (4)
Pressure filtration Belt press dewatering Air sludge drying process Centrifugation, vacuum filtration.
We would investigate the processes cited above in the next semester (VIII) and propose a solution for efficient dewatering of sludge.
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REFERENCES:(1) Huan L, Yiying J, Mahar RB, Zhiyu W, Yongfeng N (2009). Effects of ultrasonic disintegration on sludge microbial activity and dewaterability. J Hazard Matter 161:1421-1426. (2) Wakeman RJ, Tarleton ES (1999) filtration. Equipment selection modelling and process simulation. Elsevier advanced technology, Oxford. (3) Vesilind PA, Hsu CC (1997) Limits of sludge dewaterability. Water Sci Technol 36:87-91. (4) Chen G, Yeu PL, Mujumdar AS (2002) sludge dewatering and drying. Dry technol 20:883-916. (5) NEPL Lab Manual and Analysis Data.
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