Influence of evapotranspiration on wastewater treatment and electricity generation performance of constructed wetland integrated microbial fuel cell

Abstract

Evapotranspiration (ET) is a natural phenomenon of water loss through plants, which can influence the treatment performance of constructed wetlands integrated with microbial fuel cells (CW-MFC). The influence of ET on the electrochemical performance and treatment performance of CW-MFC in an actual field with real wastewater has never been studied in detail. Thus, this research aims to explore the effects of water loss ascribed by ET on different performance indicators of a CW-MFC fed with municipal wastewater in actual field conditions, for instance, voltage and power generation, internal resistance, and wastewater treatment. During the first 48 h of the operation of CW-MFC, a significant drop in the water level by 336 mm (from 15 mm to 351 mm from the top surface) in the cathode electrode zone due to ET was recorded. This water loss at the cathode enhanced cathodic reduction kinetics by increasing the oxygen saturation at the cathode, thereby improving the voltage generation from 182.5 +/- 12.5 mV (first 6 h when the cathode was more water-saturated) to 800 +/- 13.47 mV (after 48 h when the cathode was air-saturated due to loss of water), which corresponds to the current and power density of 85.71 mA/m(3) and 25.71 mW/m(3), respectively. Together with this significant coulombic efficiency (CE) and net energy recovery (NER) of 11.95 % and 2.44 Wh/kg center dot COD was achieved. The internal resistance of CW-MFC was also noted to decrease from 1000 Omega in the first 6 h to 700 Omega at the end of 48 h. After 48 h of the observation period, the CW-MFC could achieve chemical oxygen demand (COD), ammonium, and phosphate removal efficiency of 80 +/- 7.98 %, 73.17 +/- 5.01 %, and 75.60 +/- 1.65 %, respectively. This study demonstrates a substantial effect on the performance of CW-MFC due to ET water loss in the actual field. Thus, ET is a critical aspect and worth considering for large-scale implementation of CW-MFCs, especially in tropical regions or with dense plantations.