Anaerobic microbial community data under different fat loading rates.. Fats, Oils, and Grease Anaerobic Digestion

Co-digestion of fats, oils, and grease (FOG) with food waste (FW) can improve the energy recovery in anaerobic membrane bioreactors (AnMBRs). Here, we investigated the effect of co-digestion of FW and FOG in AnMBRs at fats loading of 0.5, 0.75, and 1.0 kg m-3 day-1 with a constant organic loading rate of 5.0 gCOD L-1 day-1 in both a single phase (SP) and two phase (TP) configuration. A separate mono-digestion of FW at an identical organic loading rate was used as the benchmark. During co-digestion, higher daily biogas production, ranging from 4.0 to 12.0% was observed in the two-phase methane phase (TP-MP) reactor compared to the SP reactor, but the difference was statistically insignificant (p>0.05) due to the high variability in daily biogas production. However, the co-digestion of FW with FOG at 1.0 kg m-3 day-1 fats loading rate significantly (p<0.05) improved daily biogas production in both the SP (11.0%) and TP (13.0%) reactors compared to the mono-digestion of FW. Microbial community analyses using cDNA-based MinION sequencing of weekly biomass samples from the AnMBRs revealed the prevalence of Lactobacillus and Anaerolineaceae, which are known as fermenters and fatty acid degraders. Syntrophic fatty acid oxidizers were mostly present in the SP and TP-MP reactors, possibly because of the low pH in the acid phase digesters. A greater abundance of the mcrA gene copies (and methanogens) was observed in the SP and MP reactors compared to the AP reactors. This study demonstrates that FW and FOG can be effectively co-digested in AnMBRs and is expected to inform full-scale decisions on optimum fats loading rate.