Improvements of nitrogen removal and electricity generation in microbial fuel cell-constructed wetland with extra corncob for carbon-limited wastewater treatment

Abstract

Nitrogen residues in effluent from municipal wastewater treatment deteriorate aquatic ecosystem, and the common method is to add external carbon sources. Considering the low cost and easy availability, agricultural biomasses are often applied as the external carbon sources for carbon-limited wastewater treatment. This research estimated the feasibility of adding agricultural wastes to simultaneously enhance nitrogen removal and bioelectricity generation in microbial fuel cell-constructed wetland (MFC-CW), and the results were compared to those in MFC. Different agricultural wastes (corncob, straw, rice husk) were compared, and corncob showed a higher carbon release ability. The results revealed that the carbon release of corncob was a diffusion process, and fitted the second-order kinetics with the highest released chemical oxygen demand (COD) of 47.6 mg·(g·L)−1. Corncob addition significantly enhanced the nutrients removal in MFC-CW with original influent COD of 22 mg L−1, and the maximum total nitrogen (TN), nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N) removals were 86.6 ± 1.6%, 97.2 ± 0.3%, 73.1 ± 2.8%, respectively. Besides, the bioelectricity generation performance was also promoted with the maximum voltage and power density of 340 mV and 23.5 mW/m3, whereas the internal resistance slightly increased. The findings provide an economic way for nitrogen removal, energy recovery and agricultural wastes management by MFC-CW when treating carbon-limited wastewater.