Performance and microbial community structure characterization of a CIC anaerobic reactor for the treatment of cassava wastewater

A laboratory-scale controlling internal circulation (CIC) anaerobic reactor was developed to treat cassava wastewater. The hydraulic retention time (HRT), internal circulation ratio, and temperature were selected as main operating variables that could be optimized to increase efficiency of the reactor. Responses of microbial communities to changes in these parameters were investigated using high throughput sequencing (HTS) approach. With increasing internal circulation ratio, the COD removal efficiencies and gas production rates also increased. On the other hand, decreasing temperature to 20 °C resulted to increase in the effluent COD concentration to 1000 mg L⁻¹, with low gas production rate of 0.10 m³CH₄ kg⁻¹·COD⁻¹. Upon starting the internal circle of the CIC reactor, species diversity was reduced while species abundance increased. Specifically, Methanosarcinales increased from 32.82% to 39.69%, and Methanobacteriales from 33.72% to 54.77%. However, when the CIC reactor temperature was further reduced to 25 °C, the abundance of Methanobacteria decreased to 33.35%. Results showed the microbial community shift was observed at different internal circulation ratio and temperature, influencing the pollutants removal rate and gas production rate.