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 degrees C. Meanwhile, the methane yield decreased from 0.386 to 0.232 g COD/g TCODconsumed with the decreasing temperature from 35 to 20 degrees 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 x 10(-3) kWh/m(3) at 20-35 degrees 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. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.