Field tests of cubic-meter scale microbial electrochemical system in a municipal wastewater treatment plant.

A pilot microbial electrochemical system (MES) system with a total volume of 1.5 m3 was developed and operated outdoor in a municipal wastewater treatment plant (WWTP). Microbial separator based on the dynamic biofilm on low-cost porous matrix was applied to replace ion exchange membranes (IEMs), while the separate plug-in module architecture allowed the totally 336 pairs of MES units and 14 separator modules to be integrated into one wastewater tank. The separator layer equally divided the wastewater tank into 7 cathodic and 8 anodic compartments. Fed with primary sedimentation tank effluent of WWTP, the pilot MES achieved stable removal efficiency for chemical oxygen demand (91 ± 3%), total nitrogen (64 ± 2%) and ammonium nitrogen (91 ± 3%), which were complied with the first grade A standard of pollutants for municipal wastewater treatment plant (DSPMWTP) in China. The stable power output of pilot MES was 406 ± 30 mW m-3 based on effective liquid volume, or energy conversion performance of 2.03 × 10-3 kWh m-3 (one cubic meter of influent wastewater). The pilot MES achieved much lower effluent COD of 25 ± 7 mg L-1 with HRT of 5 h, while that of activated sludge process in WWTP was 43 ± 6 mg L-1 under HRT of 12 h. Even though the aeration of biocathode demanded a net electricity consumption of 3.44 × 10-3 kWh m-3, the low operation energy requirement for pilot MES was only 12% of that in a typical activated sludge process (0.3 kWh m-3). By avoiding the utilization of IEMs and redundant structural materials, the pilot MES achieved a low system cost of $1702.1 (or $1135 m-3) as well and promoted the further real-world application of MES.