Biomethanation of organic waste, Anaerobic degradation,Degradation of organic waste

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Information about Biomethanation of organic waste, Anaerobic degradation,Degradation of...

Published on July 1, 2009

Author: salinsasi



Energy has a major economical and political role to play in the modern day society. Energy consumption in the developed countries has more or less stabilized whereas in developing countries like India and China it is increasing at a phenomenal rate. The Government is looking forward to Biomethanation as a secondary source of energy by utilizing industrial, agricultural and municipal solid wastes. A large amount of money is being invested in this direction with various projects under different stages of implementation and many to follow them. Hence the long-term sustainability of the technology needs to be judged. Various potential merits of Biomethanation like reduction in land requirement for disposal, preservation of environmental quality, etc. are the spin off of the process. A study of biomethanation plant in different developed countries and India has been carried out. To understand the technical feasibility in the Indian context, a comparison is made between the characteristics of Indian waste and the ideal wastes characteristics. Further problems of the operational stability, commercial viability of biomethanation in India, developmental plans covering issues in the formulation of national policy, improvements in collection and transportation systems, marketing strategy, and funds allocation has been highlighted .With the growing energy crisis supplemented by environmental concerns, Biomethanation can serve as a potential waste-to-energy generation alternative.
With the ever increasing awareness of green house gases and its adverse impact on the environment, pursue of Biomethanation of Municipal Solid Waste will drastically reduce the emission of CH4 and CO¬2, earning the country precious carbon credits. It will also forge India among developing countries, leading in adoption of technology which suffices the broad guidelines as laid under KAYOTO PROTOCOL.


URBAN WASTE SCENARIO • Urban India generates about 1.4 lakh MT/day of MSW • Requires 1750 acres of land for land filling/year Courtesy-MNRE







POTENTIAL OF ENERGY FROM URBAN WASTES 2007 2012 2017 MSW 1.48 2.15 3.03 (lakh tpd) MW 2550 3670 5200 MLW 17.75 20.70 24.75 (mcd) MW 330 390 460 Courtesy-MNRE

INDIAN SCENARIO • As per MSW Rule 2000, biodegradable material should not be deposited in the sanitary landfill • Therefore there is almost no scope of generation of biogas in the form of landfill gas from new sanitary landfills • However, there is a huge potential of trapping the landfill gas generated in the old dump-sites across the country, particularly the large ones with more than 5 meter thickness (height plus depth) Courtesy-MNES


WTE TECHNOLOGIES • Bio-methanation • Incineration • RDF • Gasification • Integrated systems

MERITS OF BIOMETHANATION • Reduction in land requirement for MSW disposal. • Preservation of environmental quality. • Production of stabilized sludge can be used as soil conditioner in the agricultural field. • Energy generation which will reduce operational cost. • Supplement national actions to achieve real, long term, measurable and cost effective GHG’s reductions in accordance with Kyoto Protocol.



PRINCIPLES • Complex process leading to generation of methane and carbon dioxide. • Process involves three steps (Barlaz et al 1990)  Hydrolysis  Acidification  Methanogenesis • Process can be carried out in  Single step  Two step

HYDROLYSIS • Anaerobic bacteria breakdown complex organic molecules (proteins, cellulose, lignin and lipids) into soluble monomer molecules such as amino acids, glucose, fatty acids and glycerol. • Monomers are available to the next group of bacteria. • Hydrolysis of complex molecules is catalyzed by extra cellular enzymes (cellulose, proteases and lipases). • Hydrolytic phase is relatively slow ,can be limiting in anaerobic digestion.

ACIDOGENESIS • Acidogenic bacteria converts sugar, aminoacids and fatty acids to organic acids (acetic, propionic, formic, lactic, butyric acids), alcohols and ketones (ethanol, methanol, glycerol and acetone), acetate, CO2and H2. • Acetate is the main product of carbohydrate fermentation. • The products formed vary with type of bacteria as well as with the culture conditions (temperature, pH etc).

ACETOGENESIS • Acetogenic bacteria converts fatty acids and alcohols into acetate, hydrogen and carbon dioxide . • Acetogenic bacteria requires low hydrogen for fatty acids conversion . • Under relatively high hydrogen partial pressure, acetate formation is reduced and the substrate is converted to propionic acid, butyric acid and ethanol rather than methane.

METHANOGENESIS • Methanogenesis in microbes is a form of anaerobic respiration. • Methanogens do not use oxygen to breathe, oxygen inhibits the growth of methanogens. • Terminal electron acceptor in methanogenesis is carbon. • Two best described pathways involve the use of carbon dioxide and acetic acid as terminal electron acceptors: CO2+ 4 H2 → CH4 + 2H2O CH3COOH → CH4 + CO2

Organic matter (Carbohydrates, lipids, proteins etc) Lipase, protease, pectinase Stage 1 Hydrolysis cellulase, amylase produced by hydrolytic microorganisms Carboxylic volatile acids, keto acids, hyroxy acids, ketones, alcohols, simple sugars, amino aicds,H2 and CO2 ß-oxidation, glycolysis Stage 2 Acidogenesis deamination, ring reduction and ring cleavage Short chain fatty acids (mainly acetic and formic acid) Stage 3 Acetogenesis Acetate CO2 and H2 Stage 4 Methanogenesis Methane +CO2 Courtesy-Kashyap .D.R et al ,2003



NUTRIENTS • Lower nutrient requirement compared to aerobic bacteria. • COD:N range is 700:5. • N used in synthesis of Enzymes, RNA, DNA. • Concentration of various nutrients (Speece et. al ,1996) N : 50 mg/l P : 10 mg/l S : 5 mg/l

pH • Most important process control parameter. • Optimum pH between 6.7 & 7.4 range for methanogenic bacteria (Zehnder et. al. 1982). • Excess alkalinity or ability to control pH must be present to guard against the accumulation of excess volatile acids. • The three major sources of the alkalinity are lime, Sodium bicarbonate and sodium hydroxide.

TEMPERATURE • Constant and Uniform temperature maintenance. • Three temperature range Psychrophilic range ; < 200 C. Mesopholic range ; 200 C to 400C. Thermophilic range ; >400 C. • Rates of methane production double for each 100C temperature change in the mesophilic range . • Loading rates must decrease as temperature decreases to maintain the same extent of treatment. • Operation in the thermophilic range is not practical because of the high heating energy requirement (Ronald L. Drostle – 1997)

• Study of temperature variation (Alvarez Rene et al 2007).  Forced square-wave temperature variations (i) 11 0 C and 25 0 C, (ii) 15 0 C and 29 0 C, (iii) 19 0 C and 32 0C.  Large cyclic variations in the rate of gas production and the methane content.  The values for volumetric biogas production rate and methane yield increased at higher temperatures.  The average volumetric biogas production rate for cyclic operation between 11 and 25 0C was 0.22 L d -1 L - 1 with a yield of 0.07 m 3CH kg -1 VS added (VSadd) 4

 Between 15 and 29 0C the volumetric biogas production rate increased by 25% (to 0.27 L d -1L-1with a yield of 0.08 m 3CH 4 kg -1 VSadd).  Between 19 and 32 0C, 7% in biogas production was found and the methane yield was 0.089 m3 CH4 kg-1 VSadd.  Digester showed an immediate response when the temperature was elevated, which indicates a well- maintained metabolic capacity of the methanogenic bacteria during the period of low temperature.  Periodic temperature variations appear to give less decrease in process performance than as prior anticipated.

Courtesy- Alvarez Rene et al 2007

SOLID RETENTION TIME (SRT) AND HYDRAULIC RETENTION TIME(HRT) • SRT is defined as the average time the solid particles remains in the reactor. • The anaerobic digestion is typically performed in Continuously Stirred Tank Reactor (CSTR). • The performance of CSTR is dependent on hydraulic retention time (HRT) of the substrate and the degree of contact between the incoming substrate and a viable bacterial population (Karim et al.,2005). • An increase or decrease in SRT results in an increase or decrease of the reaction extent.

MIXING • Mixing creates a homogeneous substrate preventing stratification and formation of a surface crust, and ensures solids remain in suspension. • Mixing enables heat transfer and particle size reduction as digestion progresses . • Mixing can be performed in two different ways(Kaparaju P et al,2007):  Continuous mixing – SRT is equal to HRT  Non-continuous mixing – SRT is more than HRT

• The effect of continuous , minimal (mixing for 10 min prior to extraction / feeding) and intermittent mixing (withholding mixing for 2 hr prior to extraction/feeding) on methane production was investigated in lab-scale CSTR (kaparaju P. et. al ,2007) . • On comparison to continuous mixing, intermittent and minimal mixing strategies improved methane productions by 1.3% and 12.5%, respectively.

ALKALINITY • Calcium, magnesium, and ammonium bicarbonate are examples of buffering substances found in a digester . • A well established digester has a total alkalinity of 2000 to 5000 mg/L. • The principal consumer of alkalinity in a reactor is carbon dioxide .

TOXICITY • Toxicity depends upon the nature of the substance , concentration and acclimatization . • NH 4-N concentration of 1500-3000 mg/L at 200C and pH 7.4 and above is considered stimulatory . • Anaerobic process is highly sensitive to toxicants due to slow growth rate.



BIOMETHANATION INCLUDES FOUR MAJOR ELEMENTS 1. Pretreatment. 2. Digestion. 3. Gas purification 4. Residue treatment.

PRETREATMENT • Separate out inorganic matter and materials which disrupt mechanical operation of the digester • Increase the biodegradability of the substrate. • Classification of the refuse by either wet or dry separation processes • Provides the feedstock with a high concentration of digestible matter, relatively free of metals, glass and grit • Dry separation processes offer the advantage of flexibility in selecting the desired water content • Wet separation processes operate at low solids concentrations, and have the disadvantage of requiring a dewatering step

DIGESTION • Organic feedstock is mixed with nutrients and control chemicals. • Lime and ferrous salts are added for pH and hydrogen sulfide control. • Digester operates at mesophilic conditions ( 370C ). • The conversion occurs in two steps firstly solids are solubilized or digested by enzymic action, secondly the soluble products are fermented in a series of reactions resulting in the production of methane and carbon dioxide.

PRODUCTS OF DIGESTION • Consist of two streams  The gas stream is composed of approximately equal volumes of methane and carbon dioxide.  The slurry stream is composed of an aqueous suspension of undigested organic matter.

SINGLE-STAGE HIGH RATE DIGESTION • Process done in single digester • Uniform feed is very important • Digester fed on daily cycle of 8 or 24 hours. • Digester tank may have fixed roof or floating roof.

TWO-STAGE DIGESTION • Seldom used in modern digester design. • High rate digester coupled with second tank in series. • Second tank not provided with mixing contraption. • Less than 10% of the gas generated comes from second tank

GAS TREATMENT AND HANDLING • Gas from digester contains methane, carbon dioxide and trace quantities of hydrogen sulfide. • CO2 and H2S must be removed if the methane gas is to be pumped for combustion purpose. • Standard method of removing acid gases from natural gas is by absorption with monoethanolamine (MEA), the MEA is then regenerated and recirculated. • Methane must also be dried, accomplished by a glycol dehydration process in which the moisture is absorbed in dry glycol, which is also regenerated and recirculated.


Courtesy-MNRE Project for generation of 5 MW power from Municipal Solid Waste at Lucknow (Courtesy MNRE)

ENERGY RECOVERY POTENTIAL Courtesy-Ambulkar.A.R et al 2003

ENERGY GENERATION/CONSUMPTION IN SYSTEM Energy Resources Material Resources Manure Commercial Non-conventional Biogas Biomethanation sources sources Technology Processing of waste Industrial Agricultural Degradable Utilization Consumption Inerts organic matter Human Consumption Municipal Solid waste Waste Generation Role of Biomethanation Technology Energy Generation-Consumption in System in the system Courtesy-Ambulkar.A.R et al 2003

PARAMETERS RESPONSIBLE FOR TECHNICAL FEASIBILITY OF BIOMETHANATION PLANT Parameters related with Technical Feasibility Need for obtaining waste Ensuring process kinetics Ensuring the with desired composition to be fast enough for conditioning of waste addressing the following implementation at plant at processing site with issues: scale addressing the respect to the • Annual seasonal following parameters with following points: variation in waste optimum conditions: • Removal of non- composition. • pH biodegradables • Identification of • Digester Temperature • Removal of points for collection (Thermophilic, binders like soil of waste. mesophilic conditions) particles, stones, • Source specific • Carbon to Nitrogen ratio etc. collection of waste. • Maintenance of • Adjustment of COD/BOD values of the water content in reactor feed. the feed to the reactor. Courtesy-Ambulkar.A.R et al 2003

PARAMETERS AFFECTING THE COMMERCIAL VIABILITY OF BIOMETHANATION PLANT Factors affecting the economy of plant Compromise with the Costs associated with Problems associated with Energy inefficiency associated marketing of products quality of raw material as Pre- and Post- treatment with the plant • Uncertainty in markets energy generation of the feed • Biological processing is a time source • Raw material being a for the digestate consuming process and hence represents a •MSW being a heterogeneous energy generation rates are commercial risk, which heterogeneous mixture with low. impacts on the mixture has a considerable amount • Net energy generation rate is technology’s costs. remarkable seasonal of inerts and needs low as it involves the • Other energy variation which pre-treatment. efficiencies associated with hampers the quality • Large amount of generation sources both biogas generation and will have to competitive of product wastewater is biogas combustion. edge over the biogas. generated with • The calorific value of biogas is • Compost is not yet needs an efficient comparatively less as it established as a method for treatment. contains about 50% CO2 along product marketable. with methane. Courtesy-Ambulkar.A.R et al 2003

PARAMETERS FAVORING THE COMMERCIAL VIABILITY OF BIOMETHANATION PLANT Factors enhancing the economy of plant Reduction in costs Financial Incentives from • Reduction in raw government material transportation • Financial and fiscal cost. incentives offered by the • The feed MSW is very Ministry of Non cheap and so less raw Conventional Energy material cost. Sources. • Constitutional Amendment Act and emphasis on privatization has led to the creation of this market in India. Courtesy-Ambulkar.A.R et al 2003


VALORGATM PLANT AT FRANCE • Principle The Valorga process is an anaerobic biological treatment process for waste organic fraction . • Advantages  Adapted to the treatment of organic municipal solid waste  The process operates under anaerobic conditions with a high dry solid content of 25 - 35 %, owing to a specific process design.  Anaerobic digestion leads to the production of a high methane content gas: the biogas.  Does not require a large land area.




APPROPRIATE RURAL TECHNOLOGY INSTITUTE (ARTI), PUNE Schematic description of the small ARTI compact biogas plant. Courtesy-ARTI

APPROPRIATE RURAL TECHNOLOGY INSTITUTE (ARTI), PUNE Construction of an ARTI compact ARTI biogas plant for treatment of biogas plant. kitchen waste at household level. The design, has won the Ashden Award for Sustainable Energy 2006

Bhabha Atomic Research Centre (BARC), Mumbai Courtesy-MNES

Biogas Plant at Trombay Courtesy-MNES

Parameters of BARC technology Courtesy-MNES

The Energy and Resources Institute (TERI), New Delhi Courtesy-TERI

The Energy and Resources Institute (TERI), New Delhi Waste is fed into the acidification module. UASB unit Courtesy-TERI

PROJECTS INSTALLED FOR ENERGY FROM URBAN WASTES • 6.6 MW project based on MSW at Hyderabad • 6 MW project based on MSW at Vijayawada • 5 MW project based on MSW at Lucknow • 1 MW power from Cattle Dung at Ludhiana • 150 kW plant for Veg. Market, sewage and slaughterhouse waste at Vijayawada • 250 kW power from Veg. Market wastes at Chennai.



CONCLUSION Considerable potential for enhancing the biogas production from the present stock of MSW generated in the country. Drastic reduction in the emission of CH4 and CO2, earning the country precious carbon credits. Assist in implementation of KYOTO protocol.

REFERENCES  Alvarez Rene and Liden Gunnar (2007), ‘The effect of temperature variation on biomethanation’, Bioresource Technology 99 (2008) pp 7278- 7284.  Ambulkar A.R and Shekdar A.V (2003), ‘Prospects of biomethanation technology in the Indian context: a pragmatic approach’, Resources Conservation and Recycling 40 (2004) pp 111-128.  Bhattacharyya J.K., Kumar S., Devotta S., (2008), ‘Studies on acidification in two-phase biomethanation process of municipal solid waste’, Waste Management 28 (1), 164-169. Bioresource Technology 77 (2000) pp 612-623.  Dhussa A. K and Tiwari R.C (2000), Article on Waste-to-energy in India. 12-14.  Kaparaju P, Buendia I, Ellegaard L and Angelidakia I (2007), ‘Effect of mixing on methane production during Thermophilic anaerobic digestion of manure: Lab-scale and pilot-scale studies’, Bioresource Technology 99 (2008) pp 4919-4928.  Karim K., Hoffmann R., Klasson K.T., Al-Dahhan M.H.,(2005), ‘Anaerobic digestion of animal waste : effect of mixing’, Science Technology 45, pp 3397-3606.  Kashyap. D.R, Dadhich. K. S, Sharma. S. K (2003), ‘Biomethanation under psychrophilic conditions’, Bioresource Technology 87 (2003) pp 147 - 153.  Kim I.S., Kim D.H., Hyun S.H.,(2002), ‘Effect of particle size and sodium concentration on anaerobic thermophilic food waste digestion’, Science Technology 41,pp 61-73.  Kumar D., Khare M., Alappat B.J.(2001), ‘Leachate generation from municipal landfills in New Delhi, India’.27th WEDC Conference on People and Systems for Water, Sanitation and Health, Lusaka, Zambia.  Mahindrakar AB, Shekdar AV.(2000), ‘ Health risks from open dumps: a perspective’, Bioresource Technology 63 (2000) pp 281 - 293.  Muller Christian., (2007), ‘Anaerobic digestion of biodegradable solid waste in Low and Middle income countries’, Eawag Aquatic Research.  Municipal Solid Waste (Management and Handling) Rules,(2000), MNES, Govt of India, New Delhi.

 NEERI Report (2005), ‘Assessment of Status of Municipal Solid Waste Management in Metro Cities, State Capitals, Class I Cities and Class II Towns’.  Parkin G. F,Owen, William F, (1986)*, ‘ Fundamentals of anaerobic digestion of waste water sludges’, J. Env. Engg. Div. ASCE, Vol. 112, No. 5, pp 867-920.  Ronald, L. Drostle, (1997)*, ‘Theory and practice of water and waste water treatment’, John Wiley and sons, Inc USA ( NewYork).  Sawyer, Clair N, Mc Carty, Perry L. and Gene F. Parkin (2003), ‘Chemistry for Environmental Engineering and Sciences (Fifth Edition), Tata McGraw Hill Book Company, pp 689-697.  Solid waste manual (2004), MNES, Govt of India.  Speece R.E. (1983)*, ‘Anaerobic biotechnology for Industrial waste water treatment’. Env. Sci.and Tech Vol.17, No.19, pp 416A.  Vavilin V.A., Angelidaki I., (2005), ‘Anaerobic degradation of solid material: Importance of initiation centers for methanogenesis, mixing intensity and 2D distributed model’, Biotechnology, Bioengineering 89(1), 13-122.  Zehnder, A.J, K. Ingvorsen and T. Marti (1982)*, ‘ Microbiology of methanogen bacteria in anaerobic digestion’, pp 45-68. * - Papers not referred in original


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