Denitrification in a low carbon environment of a constructed wetland incorporating a microbial electrolysis cell

The main aim of this study was to explore the possibility of denitrification under low carbon conditions in a microbial electrolysis cell (MEC) integrated into a constructed wetland (CW). To our knowledge, this is the first systematic study of the incorporation of an MEC into a CW for enhancing denitrification. CWs are an efficient and low-cost technology for wastewater treatment facing problems in denitrification under low carbon conditions. Two CW-microcosms were fabricated: one included an MEC arrangement with granular graphite electrodes attached to a power source and the other with a microcosm fabricated with normal stone gravel as a control. These microcosms were fed with synthetic wastewater containing 50 mg/l of nitrate-nitrogen (NO₃-N) with different ratios of organic carbon. Carbon to nitrogen ratio (C: N) were kept to 2:1, 1:1 and 0.5:1. The maximum concentration of organic carbon was 100 mg/l, subsequently decreased to 50 mg/l to 25 mg/l. The highest percentage removal achieved from CW-MEC in C: N ratios of 2:1 were 69.3% on 0.583 mA applied current, whereas the control microcosm’s removal efficiency on the same C:N was 66.2%. The outcomes of this study show that the NO3-N removal was always higher in the MEC integrated CW compared to the normal CW. The study concludes that the higher denitrification is possible by incorporation of an MEC into a constructed wetland under low carbon condition. This approach can provide a new direction for denitrification enhancement in a CW.