Anaerobic Digestion and Biogas Terminology and designs.
Post on 01-Jan-2016
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