Constructed wetland coupled microbial fuel cell treating real tannery wastewater: Performance, effect of filling media and anode position, and mechanisms of contaminants removal

Abstract

This study was undertaken to assess the performance of constructed wetland coupled microbial fuel cell (CW-MFC) system to treat real tannery wastewater. Five identically designed CW-MFC systems were setup and operated in a batch mode for two operational cycles. To assess the effect of filling media, CW1-MFC and CW2-MFC were filled with polypropylene granules as an innovative filling media, whereby, CW3-MFC, CW4-MFC, and CW5-MFC were packed with natural gravel. All CW-MFCs were provided with cylindrical graphite anodes, but CW2-MFC, CW4-MFC, and CW5-MFC used irregular-shaped granular graphite underneath the cylindrical anodes as supportive auxiliary anode. Cana indica was utilized as the vegetation model in four CW-MFC systems, but CW5-MFC was maintained unplanted and considered as the control system. The results demonstrated that maximum removal efficiencies of COD were in the range of 98.9%- 99.3%, while, maximum power outputs were recorded as 351.3, 622.3, 538, and 4437 mW/m3 with maximum salinity elimination efficiencies of 62%, 56%, 52%, and 56% in CW1-MFC, CW2-MFC, WC3-MFC, and WC4-MFC, respectively. Performance of the unplanted CW5-MFC was significantly comparable to the planted CW4-MFC in regard of COD removal and power generation, but with lower efficiency of salinity removal of 16.43% indicating the plant role in removal of total dissolved solids. Also, the results revealed the absence of arsenic and chromium in the treated effluent. So, besides being an effective approach for the treatment of tannery wastewater, it is a promising, operationally friendly and economically sustainable ecotechnology in the focus of wastewater reclamation and its reuse, as well as energy recovery.