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Abstract
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 fat mass 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 fat 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 (92.2–95.7% relative activity) and Anaerolineaceae (13.3–57.5% relative activity), 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 and short solid retention time (SRT) 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 acid-phase (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 the optimum fat loading rate.
Highlights
Fats, oils, and grease (FOG) from cooking and food processing industries are generally collected in grease traps and interceptors to prevent damage to sewage collection systems (Alqaralleh et al, 2016; Amha et al, 2017)
Increased biogas production was observed in the two-phase methane phase (TP-MP) reactor compared to the SP reactor at all fat loading rates; due to the high variability, the differences in biogas production rates were not statistically significant (Supplementary Figure 2)
This study demonstrated a statistically insignificant increase of biogas production in the TP anaerobic membrane bioreactors (AnMBRs) compared to the SP AnMBR during co-digestion of food waste (FW) and FOG at different fat loading rates
Summary
Oils, and grease (FOG) from cooking and food processing industries are generally collected in grease traps and interceptors to prevent damage to sewage collection systems (Alqaralleh et al, 2016; Amha et al, 2017). Management of FOG in anaerobic digesters can reduce environmental impacts by diverting it from landfills (i.e., the conventional method for FOG management), while enabling energy recovery in the form of increased biogas production from the additional substrate (Alqaralleh et al, 2016). Anaerobic membrane bioreactors (AnMBRs), which combine anaerobic digestion and membrane separation to improve effluent quality and increase biogas production, are an attractive biotechnology for organic waste management AnMBR was reported to produce 0.13–0.18 L CH4 per g of COD removed during treatment of food processing wastewater with a net energy benefit of 0.16–1.82 kWh m−3 (Galib et al, 2016)
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