Recently, a focus has been placed on the natural production of methane via anaerobic digesters due to its place in the water-energy-food nexus which aims to connect the three major sectors of urban life and sustainable development. Anaerobic digestion sits prominently in the nexus due to its ability to digest organic matter (food waste) and produce usable fertilizer as well as methane, a renewable energy source. The anaerobic co-digestion of energy-rich fats, oils, and greases (FOG) has been recognized as an effective, low-cost, and commercially viable approach to improve methane yields needed to increase energy recovery at wastewater treatment facilities. However, it is currently unknown what microbiome compositions are optimal for co-digestion nor what operational parameters are most effective at creating these optimal compositions.
This work monitored nineteen full-scale anaerobic digesters, at six separate facilities, monthly for one year to link operational characteristics with microbiome composition. Of the nineteen digesters studied, three perform FOG co-digestion, four perform co-digestion with biodiesel wash water, one is fed only TWAS (thickened waste activated sludge), and the remaining eleven are fed primary sludge and TWAS. Microbiome composition was analyzed using 16S rRNA amplicon sequencing. Operational data from each of the full-scale facilities (including pH, alkalinity, volatile fatty acids, detention time, temperature, total and volatile solids, free ammonia, organic N, dissolved P, organic P, chemical oxygen demand, and gas production) was examined to determine their influence on microbiome compositions.
Batch resistance assays were created to link microbiome compositions with digester functionality in response to organic over loadings. For each full-scale anaerobic digester tested, five batch anaerobic digesters were ran as digestate-only controls, and the remaining twenty were fed 1 mL, 5 mL, 10 mL, and 20 mL of canola oil (in quintuplet). The rates of methane production and methane content of the biogas were used to calculate the functional resistance of each full-scale anaerobic digester. The batch resistance assays were performed in winter and summer to account for seasonal variations in full-scale plant operation and microbiome compositions.