Organics and coliform removal from low strength domestic wastewater using integrated constructed wetland – microbial fuel cell reactor with bioelectricity generation

Abstract

Wastewater treatment with energy recovery is a major concern in environmental engineering research nowadays. The current study focuses on the removal of organics and fecal coliforms which are primary source of pollution in domestic wastewater, using three identical reactors. One vertical planted constructed wetland (R1), one planted CW-MFC (R2), and one unplanted CW-MFC (R3). Bioenergy production in R2 and R3 was also monitored. In terms of COD removal, R2 reactor achieved 93.13 ± 4.83% efficiency, and R1 and R3 achieved 87.21 ± 4.56% and 86.31 ± 4.37% efficiencies, respectively. BOD removal efficiency in R1, R2, and R3 reactors were found to be similar around 91.79 ± 3.58% to 92.7 ± 3.3%. The total coliform removal was better in R1 (log 2.95) than in R2 (log 2.93). However, the fecal coliform removal in R2 was much higher (log 3.51) compared to R1 (log 2.94). Coliform and organic removal deteriorated during winter time, though electricity generation remained unaffected. The maximum open-circuit voltage in R2 was 886 mV and in the R3 was 487 mV during the complete study. Plants played a positive role in enhancing the electrical performance of R2 compared to unplanted R3 by increasing the redox potential. Presence of dissolved oxygen in the range of 1.97–2.1 mg/L was also detected near the rhizosphere of the planted reactors. Combined role of plants and electrodes was crucial for COD removal and anaerobic condition near anode with low ORP governed the pathogen removal from domestic wastewater.