Potential of novel wastewater treatment system featuring microbial fuel cell to generate electricity and remove pollutants

• A new design of membrane-free pilot-scale constructed wetland-microbial fuel cell was performed here.
• The CW-MFC worked well as continuous bioelectricity produced and high pollutants removal rates were obtained.
• Temperature and influent COD concentration influenced the electricity generation of the system.
• It implied a new way by applying and magnifying CW-MFC to practical operation.

A new design of a pilot-scale constructed wetland managed with a membraneless microbial fuel cell (CW-MFC) was tested here to assess its potential to generate electricity and remove pollutants under different operating conditions. In the CW-MFC, the cathode was half vertically inserted into the matrixes of constructed wetland (CW) and half exposed to the air to benefit from both surrounding wetland plant growth and the atmosphere thereby ensured its demand for oxygen as well. A series of periodic and regular voltages were obtained after four cycles of wastewater treatment in the batch flow experiment with influent chemical oxygen demand (COD) 228 mg/L. The maximum voltage output (0.588 ± 0.01 V) for these four cycles lasted for 34, 35, 37 and 42 h, respectively. A steady set of maximum voltage (0.529 V) outputted over a wetland operation period of 15 days in the continuous flow experiment with the hydraulic retention time of 10 h. The maximum power density was 9.6 mW/m2 and the maximum current density was 55 mA/m2 according to the cathode area. Under batch flow mode, the COD removal rate was 91.2% and the outstanding removal rates of total nitrogen, ammonium nitrogen and total phosphorus appeared ranging between 95% and 99% while electricity generated from the CW-MFC. The influence of temperature on electricity generation was investigated and the result showed that the maximum voltage output values were inversely relative to the lasting duration of the voltage. Influent COD concentrations also affected the highest voltage output and continuous electricity generation of CW-MFC, and the higher initial COD concentration elevated the electricity generation. Thus, the new CW-MFC has high potentials not only of bioelectricity generation but also of the high pollutant removal rates.