Energy capture and nutrients removal enhancement through a stacked constructed wetland incorporated with microbial fuel cell

To improve the sustainability of constructed wetlands (CWs), a novel tiered wetland system integrated with a microbial fuel cell (MFC) was developed in this study. Compared to the single stage CW, chemical oxygen demand (COD) removal efficiency was improved from 83.2% to 88.7%. More significantly, this tiered system significantly enhanced total nitrogen removal efficiency (an increase from 53.1% to 75.4%). In terms of MFC integration, a gradually decreased performance in electricity production was observed during its 3 months of operation (the voltage dropped from nearly 600 mV to less than 300 mV), which resulted in a reduction of power density from around 2 W/m³ to less than 0.5 W/m³. The deterioration in performance of the air-cathode is the main reason behind this, since the electrode potential of the cathode under open circuit reduced from 348.5 mV to 49.5 mV while the anode potential kept constant at around −400 mV. However, in spite of its electrical performance reduction, it was proved that MFC integration enhanced COD removal and the nitrification process. Further work is needed to improve the stability and feasibility of this new system.