Operating a two-stage microbial fuel cell–constructed wetland for fuller wastewater treatment and more efficient electricity generation

By integrating microbial fuel cells (MFCs) into constructed wetlands (CWs) the need and cost of building a reactor are eliminated, while CWs provide the simultaneous redox conditions required for optimum MFC performance. Two single-stage MFC-CWs, with dewatered alum sludge cake as the main wetland medium for enhanced phosphorus removal, were operated to determine the effects of electrode separation and flow regimes on power production and wastewater treatment. When the anode is buried and the cathode is at the air–water interface the system is inhibited by a large ohmic resistance resulting from the increased electrode separation. By placing the cathode directly above the anode and operating the system with simultaneous upflow into the anode and downflow into the cathode the ohmic resistance is reduced. The chemical oxygen demand (COD) removal efficiency was, however, reduced to 64% (compared with 79%). A two-stage system was subsequently run for fuller wastewater treatment and increased power production. The results indicate that a two-stage MFC-CW can increase the normalized energy recovery and improve removal efficiencies of COD, total nitrogen, NH4+, total phosphorus and reactive phosphorus to 93 ± 1.7%, 85 ± 5.2%, 90 ± 5.4%, 98 ± 5.3% and 99 ± 2.9%, respectively.