High-rate stabilization of primary sludge in a single-chamber microbial hydrogen peroxide producing cell

This study investigates the effect of sludge stabilization at high rates on a single-chamber microbial hydrogen peroxide (H2O2) producing cell (sMPPC). Unlike a typical microbial fuel cell operation, the use of the sMPPC focuses on sludge treatment instead of power generation. Two different porous separators between the anode and the cathode, glass fiber (GF) and stitchbond polyester fabric (SPF), as well as two circuit modes, closed and open, were explored. The sMPPC in the open-circuit mode (no current generation) had a COD removal rate of 0.89 g COD per L per day (removal flux of 22 g COD per m−2 d−1) due to only passive oxygen diffused through the air-cathode. The sMPPC in the closed-circuit mode equipped with SPF increased the removal rate up to 2.4 g COD per L per day (loading rate of 5 g COD per L per day). The high removal rate resulted from current production, oxygen diffused through the air-cathode, and H2O2 produced, and was higher than that of a conventional anaerobic digester. This arrangement achieved a 52% VSS removal rate and 1.2 × 105 most probable number per gram solids of fecal coliforms, and the values met two important requirements (pathogen indicators and vector attraction reduction) for class B biosolid production. The microbial community in the sMPPC showed stratification of microorganisms at the anode, supporting its crucial roles in aerobic metabolism as well as anaerobic hydrolysis, fermentation, and anode respiration. We demonstrate for the first time how the sMPPC allows direct sludge stabilization at higher organic loads than traditional anaerobic digesters.