Development of a Novel Microbial Fuel Cell for Nutrient Recovery from Synthetic Municipal Wastewater

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Microbial fuel cell (MFC) is currently considered as a promising technology for wastewater treatment. This study aims to evaluate the feasibility of a double-chamber MFC to remove nutrients toward their recovery from municipal wastewater. In this scenario, the nutrient recovery can be obtained with the MFC reactor and there is no need of adding chemicals for the pH increase. Besides, energy recovery can also be achieved, which could increase the economic feasibility of this recovery system. Results showed that phosphate ions were not detected in the catholyte when the anode chamber and cathode chamber were not hydraulically connected; in contrast, the accumulation of ammonium was achieved in the cathode chamber under this situation. When anode effluent was used as the influent of the cathode compartment, nutrients can be recovered by chemical precipitation at high pH generated by the MFC itself while supplying aeration in the cathode chamber. Besides, partial phosphate and ammonium were removed by microbial absorption in the anode compartment. It was found that double-chamber MFC with the cation exchange membrane (CEM) as the separator reported the best nutrients removal compared to the forward osmosis membrane and nonwoven acting as the separator. Therefore, the MFC with CEM serving as the separator was utilized in the subsequent experiments. The impacts of organic loading rate (OLR) (435-870 mgCOD/L·d) on nutrients recovery via the double-chamber MFC for treating domestic wastewater were also evaluated. Experimental results suggested the MFC could successfully treat municipal wastewater with over 90% of organics being removed at a wider range of OLR from 435 to 725 mgCOD/L·d. Besides, the maximum power density achieved in the MFC was 254 mW/m² at the OLR of 435 mgCOD/L·d. Higher OLR may disrupt the recovery of PO₄³⁻-P and NH₄⁺-N via the MFC. The same pattern was observed for the coulombic efficiency of the MFC and its highest value was 25.01% at the OLR of 435 mgCOD/L·d. The dual-chamber MFC was then continuously operated under different influent concentrations of ammonium-nitrogen (5 to 40 mg/L). Experimental results demonstrated that this MFC reactor achieved > 85% of COD removed. Moreover, excess ammonium concentration in the feed solution may compromise the generation of electricity. Simultaneously, the recovery of phosphate achieved in the MFC was not significantly influenced at the wider influent ammonium concentration. In contrast, a high concentration of ammonium may not be beneficial for its recovery. In addition, the effect of hydraulic retention time (HRT) on the recovery of nutrients by the MFC system was studied. The COD removal rates were relatively stable while varying HRT from 0.35 to 0.69 d, which were over 92%. Similarly, the changes in the recovery rate of nutrients were negligible while increasing the HRT. In contrast, the maximum power generation declined when HRT increased.
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