Facultative-like anaerobic packed bed reactor treating low strength wastewater: microbial community and energy balance appraisements

This study explored the microbial community and the energy requirement of an anaerobic packed bed reactor (APBR) treating a low-strength synthetic wastewater (200 mg COD/L). The APBR was run with different hydraulic retention times (HRTs) and temperatures. Results show that the COD removal decreased from 89 to 46% when the HRTs and the temperature were both gradually reduced to 1 h and 20°C. Meanwhile, the methane yield decreased from 0.386 to 0.232 g COD/g TCODconsumed with the decreasing temperature from 35 to 20°C at 1-h HRT. This low methane production was associated with a low relative abundance of 0.575–0.628% for the archaea group in genus level. Genus Methanosaeta with 0.307–0.388% relative abundance represented 53–62% of the archaea group whereas facultative Trichococcus with 7.3–11.3% relative abundance was dominant in the microbial consortia. Candidatus Moduliflexus found was the second largest microbial population with 4.2–6.1% relative abundance. This facultative environment was observed in the APBR, resulting in 18–37% COD unbalanced. The energy appraisement resolved that the total electrical energy required for the APBR was consistent at 4.192 × 10−3 kWh/m3 at 20–35°C to yield the net energy ratio of 5.97–15.29. The facultative-like APBR treated the low strength wastewater efficiently while the energy input was balanced by its self-produced methane energy. [Display omitted]