Enve 330 –Solids Waste Engineering Term Project Anaerobic Digestion of OF Municipal Solid Waste 10/06/2009 Gozde Yilmaz Reyhan Sengur Sedat Kekec Ugur Kucukbayrak

What is the anaerobic digestion(AD)? AD process is degradation of organic material in the absence of oxygen and the presence of anaerobic microorganisms. It produces mainly 55 % methane and 45 % carbon dioxide gas and a compost product suitable as a soil conditioner. AD can be classified as net energy producer process. Primary goal of anaerobic digestion is energy production and volume reduction and waste stabilization are second goals of processes.

Which steps take place? 1. Hydrolysis/liquefaction: The complex polymeric matter is hydrolyzed to monomers. Lipids Polysaccharides Protein Nucleic Acids Fatty Acids Monosaccharides Amino Acids Purines & Pyrimidines Acidogenesis: Breakdown of the remaining components by acidogenic(fermentative) bacteria.End product:VFAs,By products: NH 3, CO 2,H 2 S Acetogenesis: Monomers are converted to simple organic acids, carbon dioxide and hydrogen 2 CO 2 (aq) + 4H 2 (aq) = CH 3 COOH (aq) + 2H 2 O 4. : 4. Methanogenesis: Methane is produced by bacteria called methane formers( methanogens). CH 3 COOH CH 4 + CO 2 2C 2 H 5 OH + CO 2 CH 4 + 2CH 3 COOH CO 2 + 4H 2 CH 4 + 2H 2 O

Key Parameters of AD Processes C/N Ratio A C/N ratio of 20 – 30 is considered to be optimum for an anaerobic digester. Carbon/Nitrogen ratio of MSW is estimated as 40. *Why C/N ratio is a key parameter* If C/N ratio is very HIGH, Rapid consumption of nitrogen by microorganisms No longer reaction on the left over carbon content,low gas production. If the C/N ratio is very LOW. Ammonia accumulation. Increase in pH Toxic effects on methanogenic bacterial population.

Key Parameters of AD processes 67 pH Value: Optimum biogas production is achieved when the pH value of the input mixture is between 6 and 7. Temperature: There are mainly two temperature ranges that provide optimum digestion conditions; For mesophilic range: 20°C-40°C(as optimum 30°C-35°C. ) For thermophilic :between 50°C-65°C Retention Time: The retention time for wastes treated in mesophilic digester range from 10 to 40 days. Lower retention times are required in digesters operated in the thermophilc range Mixing: The purpose of mixing in a digester is to blend the fresh material with digestate containing microbes.

MSW in AD Process Pretreatment: The waste received by AD digester is usually source separated or mechanically sorted. The purpose of separation is to remove of undesirable or recyclable materials such as glass, metals, stones. In source separation, recyclables are removed from the organic wastes at the source. Mechanical separation can be employed if source separation is not available. The waste is shredded before it is fed into the digester. Pretreatment Waste Digestion Gas Recovery Residue Treatment

Figure 1: Flow Diagram of AD

Figure 2: A Figure Shows Inside the Reactor Figure 3: An Anaerobic Digestion Plant

Waste Digestion: Feed is diluted to achieve desired solids contentand remains in the digester for a designated retention time. Different kind of water sources can be used such as clean water, sewage sludge, or re-circulated liquid from the digester effluent. Joint treatment of MSW with animal manure/sewage slurry is a popular method in existing plants,economically more viable than a MSW only treatment system. Gas Recovery: Biogas can be used for various applications, such as for cooking, lighting, Electricity production etc., Residue Treatment: In case of residue treatment, the effluent from the digester is dewatered, and the liquid recycled for use in the dilution of incoming feed. The biosolids are aerobically cured to obtain a compost product.

Types of Anaerobic Process Single Stage: All of the biological reactions occur within a single sealed reactor or holding tank. Lower construction cost w/multi stage processes. Less control of the reactions occurring within the system. Acidogenic bacteria reduce the pH of the tank BUT methanogenic bacteria operate in a strictly defined pH range The biological reactions of the different species in a single stage reactor can be in direct competition with each other. There are special process applied by countries; - Dranco Reactor - Kompogas Reactor - Valorga Reactor

Different Processes in Use Other Than Turkey Dranco Process: Feed is introduced from the top and digested matter is taken from the bottom. No mixing due to downward plug-flow of the waste. Part of the extracted matter is reintroduced with the new feed while the rest is de-watered to produce the compost product. Kompogas Process: The process works similarly, except the movement takes place in plug flow in a horizontally disposed cylindrical reactor. Mixing is accomplished by the use of an agitator. Valorga Process: The reactor is a vertical cylindrical reactor divided by a partial vertical wall in the center. The biogas, periodically injected with high pressure at the bottom of the reactor, allows efficient vertical mixing

Types of Process according to TS content Low-Solid High Solid - Solids concentrations is between. 4-8%. Disadvantages: - Considerable amounts of water must be added to wastes to bring the solids content to 4- 8%. -Residue material has to be dewatered. -Solids content of higher than 20%. Advantages: -Lower water requirements, - Higher gas production per unit volume of reactor size. Disadvantages: -Operation of the biochemical reactions at high solid content., -Handling problems(etc.pumping and mixing the solid streams.)

Dranco Process Feed Kompogas Process Biogas Digestate FeedBiogas recirculation for mixing Valorga Process

It can be seen that most of the plants are operating in Europe (91%), with some in Asia (7%) percent and a few in the US (2%). Germany is the leader with 35% of all AD plants, followed by Denmark (16%) and Sweden and Switzerland and Austria (8%). Distribution of AD Plants in World

India A BIOTECH plant treating organic solid waste on an institutional level. Municipality Co-Generation PlantChina Thailand

Applications in Turkey Anaerobic digestion process is a new subject for organic fraction MSW. There is not any anaerobic digestion plant but ISTAC A.S. is considering construct an AD plant. Planned plant will have 1MW capacity and produce energy from manure, organic wastes, yard wastes etc. Biogas will be used for heating and electricity and processed waste will be used as fertilizer. Istanbul Technical University and TUBITAK conduct this project in pilot plant and they produced 630±200 L/day biogas and 69% methane and 31% CO2.

Figure 4: A view from planned AD Plant in Turkey

Why Anaerobic digestion mSW? High energy prices all over the world Stringent environmental regulations especially controls on organic matter going to landfills as well as further expansion of landfills. Biological route for the recovery of nutrients from the organic fraction of MSW. Biogas generates less air pollution(clean energy source) by the combustion instead of fossil fuels. For developing countries efficient and sustainable solution for solid waste management.

Comments For Turkey Important subjects that have to be researched ; Biogas plants types must be adjust to the location conditions, Finding cheap and local isolation materials, Determining how to get biogas from vegetable wastes, Fertilizer obtained from anaerobic digestion plant how affects plants or soil, Determining how biogas contributes environmental health, Determining how anaerobic digestion technology affects socioeconomic life in rural areas.

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