Evaluation of electrode separators and the external resistance in electrochemically assisted constructed wetlands

A proton exchange membrane increases the electrical performance of a microbial fuel cell (MFC). New inexpensive materials should be sought, especially in a constructed wetland microbial fuel cell (CW-MFC). Here, in a laboratory-scale system of five CW-MFCs, wet clay, wet earth or mud, and non-woven cloth were used as inexpensive separators with long-term stability. The five CW-MFCs were planted with Typha latifolia, fed with synthetic wastewater, and packed with natural porous material. Graphite felt was used as electrodes and the experimental system had a hydraulic residence time of 3 days, operating under shade and natural conditions of temperature and light. Electrodes were connected to current collectors (copper wire) and to an external resistance, with a change every 20 days, starting in open-circuit and following with 20000, 18000, 15000, 10000, 5600, 1000, 560, and 10 Ω. These laboratory-scale CW-MFCs reduced concentrations of nitrates, ammonium ion, and sulfates without inhibiting electricity production. Microbiological analyses indicated that anaerobic, facultative, aerobic, and denitrifying bacteria may have caused these reductions. The reactor with the live plant and with the wet earth or mud separator achieved the highest production of electricity (22.6 mW/m²), and may be worth further attention.