Refractory azo dye wastewater treatment by combined process of microbial electrolytic reactor and plant-microbial fuel cell

An innovative design of microbial electrolytic reactor (MER) coupled with Ipomoea aquaticaForsk. plant microbial fuel cell (IAF-PMFC) was developed for azo dye wastewater treatment and electricity generation. This study aims to assess the sequential degradation of azo dye and the feasibility of energy self-sufficiency in the MER/IAF-PMFC system. The decomposition of azo dye into aromatic amines and dye decolorization occurred in the MER at high hydraulic loading of 0.28 m³/(m²·d), while dye intermediates were mainly mineralized in the IAF-PMFC at low hydraulic loading of 0.06 m³/(m²·d). The final decolorization efficiency and COD removal of the combined system reached 99.64% and 92.06% respectively, even at influent dye concentration of 1000 mg/L. The effects of open/closed circuit conditions, presence/absence of aquatic plant and different cathode areas on the performance of the IAF-PMFC for treating the effluent of the MER were systematically tested, and the results showed that closed-circuit condition, plant involvement and larger cathode area were more beneficial to decolorization, detoxification and mineralization of dye wastewater, bioelectricity output, plant growth and photosynthetic rate. The power consumption by the MER was 0.0163 kWh/m³ of dye wastewater, while the highest power generation of the IAF-PMFC reached 0.0183 kWh/m³. The current efficiency of the MER for dye decolorization was as high as 942.83%, while the maximum coulombic efficiency of the IAF-PMFC for intermediates metabolism was only 6.30%, which still had much space of bioelectricity generation promotion. The MER/IAF-PMFC technology can simultaneously realize refractory wastewater treatment and balance of electricity production and consumption.