Effects of solids retention time on the biological performance of a novel microalgal-bacterial membrane photobioreactor for industrial wastewater treatment

Abstract

Microalgal-bacterial membrane photobioreactor (MB-MPBR) takes the distinctive advantage of simultaneously removing nutrients and organics from sewage in a single step, which might be a promising technology for the treatment of industrial anaerobic digestion effluent with high strength organics and nutrients. The feasibility of using MB-MPBR to treat industrial anaerobic digestion effluent was studied at three solids retention time (SRT) for almost 300 days. The results showed that the total biomass concentration was positively correlated with SRT, increasing from 1.34 ± 0.32 g/L at SRT of 10 d to 3.40 ± 0.15 g/L at SRT of 30 d. However, the growth status of microalgae was nonlinearly correlated to SRT and the highest microalgae content was observed at SRT of 20 d. The removal of chemical oxygen demand maintained constant in the range of 90−94%, while the nitrogen and phosphorus removals significantly changed with SRT. The highest removal of total nitrogen (19.26 ± 4.58%) and total phosphorus (54.95 ± 4.36%) was found at SRT of 20 and 30 d, respectively. Moreover, the flocs size and micromorphology of the microalgal-bacterial flocs were greatly affected by SRT. Overall, MB-MPBR is a capable technique to simultaneously remove organics and nutrients from high-strength anaerobic digestion effluent. However, high concentration of nutrients in the feed and improper SRT value negatively impacted the microalgae growth and nutrients removal, which led to the dissatisfactory effluent quality. Therefore, influent dilution, a longer hydraulic retention time and intermediate SRT is required to achieve high-quality permeate fulfills the discharge standards.