Feedstock and microbial community analysis for a mesophilic co-fermentation anaerobic digestion facility

Eight substrates comprising 90% of the feedstock from a two-stage, mesophilic anaerobic digestion biogas plant located in Oroville, CA were evaluated at lab scale for their total solids/volatile solids content, biomethane potential, and micro/macronutrient concentrations in order to determine their biomethane potential in anaerobic digestion. Specific biomethane potentials from 20-day trials for eight types of substrate were trap grease (735 ml/g TS) cheese whey (452 ml/g TS), potatoes (328 ml/g TS), apple waste (460 ml/g TS), olive waste (626 ml/g TS), salami waste (709 ml/g TS), cow manure (191 ml/g TS) and food waste (579 ml/gram TS). Substrates representative of four different macronutrient groups including lipids (trap grease), proteins (cheese whey), carbohydrates (potatoes), and simple sugars (apple waste) were tested in biogas potential trials with samples collected at five time points over a 10-day period. DNA was extracted and sequenced from each sample using Ion Torrent PGM to determine if the community structure of bacteria and archaea changed in response to a change of feedstock composition. No significant changes in the bacterial community and only minor changes in the archaea community were observed suggesting that microbial communities stemming from mixed substrate co-fermentation biogas reactors are well suited to a wide variety of substrates. Further, these microbial communities appear slow to respond to a sudden shift in feedstock type. This result contrasted with other feedstock related community studies which saw large community shifts in inoculum stemming from a single substrate inoculum source. This implies the co-fermentation facilities which operate on substrates stemming from different macronutrient types may contain microbial communities which are more resilient to changes in feedstock composition.