Phosphorus recovery from artificial wastewater by microbial fuel cell and its effect on power generation.

The effects of ammonium (NH4) and magnesium (Mg) on the precipitation of phosphorus in artificial wastewater by an air-cathode single-chamber microbial fuel cell were investigated. When both NH4 and Mg were added to the wastewater, phosphorus was precipitated as struvite. Almost no precipitation occurred with the addition of only NH4, while phosphorus was precipitated as cattiite with the addition of only Mg. However, the amount of precipitate was less than that observed in experiments in which NH4 was also added. As the amounts of NH4 and Mg were increased, more precipitate was observed. Precipitated phosphorus on the cathode was recovered by dissolution in Milli-Q water and MES buffers. It was discovered that the formation of a precipitate reduced the performance of the cathode. Dissolution treatment caused the performance of the cathodes to increase to their initial level.

Removal and recovery of phosphorus as struvite from swine wastewater using microbial fuel cell.

Air-cathode single chamber microbial fuel cells (MFCs) were operated with swine wastewater. The maximum power density, the maximum current density, the average value of COD-removal efficiency, and the coulombic efficiency were 1-2.3 W/m(2), 6.0-7.0 A/m(2), 76-91%, and 37-47%, respectively. During operation, 70-82% of the phosphorus was removed from the influent, and some precipitations were observed on the surface of the liquid side of the cathodes. The amount of phosphorus contained in these precipitates was estimated to be equivalent 4.6-27% of the influent. The main component of these precipitates was revealed by X-ray diffraction analysis to be struvite. Furthermore, our results indicate that phosphorus in suspended solid form was first dissolved, and then precipitated on the cathode. By scanning electron microscope observation, the morphology of the precipitates was irregularly shaped, including crystals with hexagonal cross-section surfaces, and was different from the familiar needle-like ones. These results indicate that simultaneous recovery of electrical power and phosphorus from wastewater by microbial fuel cell is possible.

Sludge-sludge interaction in the enhanced biological phosphorus removal process.

Metabolisms related to enhanced biological phosphorus removal (EBPR) were found to be affected when two activated sludges with different EBPR activities were mixed together. In the present study, two laboratory scale EBPR processes were operated in parallel, one of them with higher and another with lower EBPR activities. The activated sludges from the two reactors were mixed together at different mixing ratios. The supernatant was made the same for all mixing ratios, anaerobic-aerobic batch experiments were performed, and acetate uptake rate and phosphate release rate under anaerobic conditions and phosphate uptake rate under aerobic condition were determined. The metabolic rates measured were expected to be linear to the mixing ratios, as the supernatant was the same for all mixing ratios, whereas the metabolic rates were either promoted or inhibited by mixing of sludges. As an indicator for the sludge mixing effect on the metabolic rates, mixing effect intensity (MEI) was introduced. Chemical substances that are produced by microorganisms in activated sludge are proposed to be one of the possible causes of the sludge mixing effect.