anaerobic digestion

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EVN 6114March 24, 2015Anaerobic digestion --a biological solid waste treatment technologyPresented by Emmanuel George

OverviewWhat is Anaerobic Digestion?ProcessProcess stagesHydrolysis Acidogenesis Acetogenesis Methanogenesis Batch and continuous process Residence time.Application Products Conclusion Reference

What is anaerobic digestion?Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.Used both industrially and domestically to produce fuelAnaerobic digestion is widely used as a source of renewable energy

mechanical biological treatment plant in Germany

Process Bacteria break down biomass (food waste)in the absence of oxygen, in temperature controlled sealed vessels and produce biogas which is typically made up of 60% methane and 40% carbon dioxide .microorganisms responsible for digesting the sludge's anaerobically are often classified in two groups, the acid formers and the methane formers.

There are basically 3 stepsPreparing the waste , by reducing the size.Constantly mixing the sludge with moisture, nutrients and pH neutralizers while heating it to 60 degree Celsius and holding it for the required time.Collecting the generated gas and disposing the digested solids.( for each pound of undigested solids we get 8- 12 cubic feet of gas in which 60% is methane.

Anaerobic Digestion process

Process stages

Batch & continuous process Continuous process Organic matter is constantly added or added in stages.Here the end products are completely removed. Resulting constant production of biogas.Single or multiple digesters in sequence may be used .Continuous gas supply and fast process residence time is less.More equipment , more design work

Batch process Biomass added at the start of the process, then the reactor is sealed for the duration of the process. Simple batch process needs inoculation, with the already processed material to start digestion. this will have odor issues if opened before process is complete. Advanced batch process has less odor issues because it uses the after digested biomass is kept in the reactor for composting.Lower design work, less equipment , more than one tank ensures constant gas production.

Residence time The residence time in a digester varies with the amount and type of feed material, the configuration of the digestion system, and whether it be one-stage or two-stageresidence times may be in the region of 14days In two stage it may vary from 15- 30 days.

Application Waste treatmentPower generationreduce the emission of greenhouse gases Reduce fossil fuelsDisplacing industrially produced chemical fertilizers Reducing usage of LP Gas for cooking.

Products BiogasMethane --60-80%Carbon dioxide 20-40%Nitrogen 0-10%Oxygen -- 0-1%Digestate used as fertilizers replacing the industrially produced fertilizers Waste-Water this is because of the moisture content present that was introduced in the preparation stage and this is reused/recycled back to the preparation process.

Conclusion What is anaerobic digestion

References Digestion--Gregory D. Boardman.Environmental Encyclopedia.