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


  • Anaerobic Digestion and BiogasTerminology and designs

  • 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

  • Total Solids, Volatile SolidsTotal SolidsAsh

  • 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

  • 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

  • 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

  • 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

  • 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.

  • 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

  • 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.

  • Different digester typesBatch vs. ContinuousTwo phaseCSTRUASBFixed-film

  • Batch vs. continuously fedBatch Digester loaded once, emptied once fully degradedContinuously fed Digester regularly loaded (usually daily), effluent produced at each loading

  • 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

  • Two phase digestion

  • CSTRContinuously-Stirred Tank ReactorSimple but effective design

  • UASBUp-flow Anaerobic Sludge BlanketFrequently used for sewage wastewater

  • Fixed Film ReactorIncreased substrate-bacteria contactUtilizes biofilmsShort HRTDecreased sizeUsed as DRU

  • Digesters in developing nationsBag digester, Costa RicaSmall scale digester, rural India

  • Digesters in agricultureCovered Lagoon, Tulare, CACorn sillage digester, Neumunster, Germany

  • Digesters in industrial settingsLbek mechanical biological treatment plant, GermanyMechanical biological treatment plant, Tel Aviv, Israel

  • Digesters as architectural features?Reading Sewage Treatment Works, Reading, United Kingdom

    Appleton Wastewater Treatment Plant, Appleton, Wisconsin

  • Questions?


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