Effect of effluent recirculation rate on the performance of anaerobic bio-filter treating coal gasification wastewater under co-digestion conditions

In this paper, anaerobic biofilters (AF) were adopted for anaerobic co-digestion of potato starch wastewater (PSW) and coal gasification wastewater (CGW). A modified Gompertz equation was used for the analysis. With a ratio of PSW:CGW at 1:1 for the influent, it remarkably improved the removal effect of (chemical oxygen demand) COD and total phenol. With an influent concentration of COD of 2600 mg L−1 and total phenol 200 mg L−1, the effluent COD and total phenol could be decreased to 1100 mg L−1 and 100 mg L−1, respectively. The methane production rate was generally above 260 (mL CH4 per g per d). In order to further enhance the performance of the system, the strategy of effluent recirculation on co-digestion was adopted. The result indicated that under a low effluent recirculation rate of 0.5, concentrations of COD and total phenol in effluent could reach as low as 800 and 70 mg L−1, respectively. Also, the methane production rate was around 300 (mL CH4 per g per d). High-throughput sequencing showed the microbial phyla Bacteroidetes, Chloroflexi, Euryarchaeota, Firmicutes dominanted the system and the abundance variation was observed at different effluent recirculation rates.