Anaerobic Digestion and Biogas

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Anaerobic Digestion and Biogas. Terminology and designs. Total Solids, Volatile Solids. Total Solids (TS)= Dry weight of substrate Volatile Solids (VS)= Combustible proportion of TS, organic matter - PowerPoint PPT Presentation

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<ul><li><p>Anaerobic Digestion and BiogasTerminology and designs</p></li><li><p>Total Solids, Volatile SolidsTotal Solids (TS)= Dry weight of substrateVolatile Solids (VS)= Combustible proportion of TS, organic matterNon-volatile Solids (Ash) = Minerals etc. left over from combustion</p></li><li><p>Total Solids, Volatile SolidsTotal SolidsAsh</p></li><li><p>COD/BODChemical/Biochemical Oxygen DemandMeasures amount of oxygen required to degrade a substrateUsed widely in aerobic water treatmentCharacterizes wastewaters and organic feedstocksEstimates energy content of substrate</p></li><li><p>BMPBiochemical Methane Potential AssayDeveloped as correlative test of BOD in anaerobic systemsRealistic measure of total methane potential of a feestockCan determine non-biodegradable materials in feedstock</p></li><li><p>Organic loading rateRate at which feedstock is fed to the digester (i.e. g VS / L reactor)Varies by feedstock, reactor type, temperature, etc.Too low= too large of reactorToo high= overload reactor, acidification</p></li><li><p>Hydraulic Retention TimeHow long substrate remains in active volume (i.e. turnover rate)Optimized for higher biogas/ reactor volume ratioToo high= Unnecessarily large reactorToo low= Reduced biogas output, washout microbes</p></li><li><p>TemperatureAnaerobic metabolism much more sensitive to temperature than aerobicMethanogens more affected than acidogensLeads to unbalanced pH at low temps.Loading rate reduced at low temps.</p></li><li><p>Mesophilic vs. ThermophilicTemperature classes for microbes in digesterMesophilic (30-40C), Thermophilic (50-60C)Different microbial communities operate at each temp. classMost digesters operate at mesophilic</p></li><li><p>pHVery important parameterOptimum 7.0, acceptable 6.0-8.0Methanogens cannot function at low pH. Ammonia toxicity above 8.0Slow recovery after sustained drop in pH.</p></li><li><p>Different digester typesBatch vs. ContinuousTwo phaseCSTRUASBFixed-film</p></li><li><p>Batch vs. continuously fedBatch Digester loaded once, emptied once fully degradedContinuously fed Digester regularly loaded (usually daily), effluent produced at each loading</p></li><li><p>Two phase digestionSingle phase- all in one reactorTwo phase- acidogenesis and methanogenesis separatedBenefitsIncreased over-all efficiency (short HRT of acidogenic reactor)More pH control of methanogenic reactor</p></li><li><p>Two phase digestion</p></li><li><p>CSTRContinuously-Stirred Tank ReactorSimple but effective design</p></li><li><p>UASBUp-flow Anaerobic Sludge BlanketFrequently used for sewage wastewater</p></li><li><p>Fixed Film ReactorIncreased substrate-bacteria contactUtilizes biofilmsShort HRTDecreased sizeUsed as DRU</p></li><li><p>Digesters in developing nationsBag digester, Costa RicaSmall scale digester, rural India</p></li><li><p>Digesters in agricultureCovered Lagoon, Tulare, CACorn sillage digester, Neumunster, Germany</p></li><li><p>Digesters in industrial settingsLbek mechanical biological treatment plant, GermanyMechanical biological treatment plant, Tel Aviv, Israel</p></li><li><p>Digesters as architectural features?Reading Sewage Treatment Works, Reading, United Kingdom</p><p>Appleton Wastewater Treatment Plant, Appleton, Wisconsin</p></li><li><p>Questions?</p></li></ul>