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Enhanced nitrate reduction in water by a combined bio-electrochemical system of microbial fuel cells and submerged aquatic plant Ceratophyllum demersum

Xu, Peng, Xiao, Enrong, Wu, Junmei, He, Feng, Zhang, Yi, Wu, Zhenbin
Journal of environmental sciences (China) 2019 v.78 pp. 338-351
Ceratophyllum demersum, Flavobacterium, Geobacter, Pseudomonas, Rhodobacter, algae, cathodes, denitrification, electrochemistry, eutrophication, lakes, microbial fuel cells, nitrate reduction, nitrates, oxygen, power generation, sediments, stable isotopes, submerged aquatic plants, surface water
High nitrate (NO3−) loading in water bodies is a crucial factor inducing the eutrophication of lakes. We tried to enhance NO3− reduction in overlying water by coupling sediment microbial fuel cells (SMFCs) with submerged aquatic plant Ceratophyllum demersum. A comparative study was conducted by setting four treatments: open-circuit SMFC (Control), closed-circuit SMFC (SMFC-c), open-circuit SMFC with C. demersum (Plant), and closed-circuit SMFC with C. demersum (P-SMFC-c). The electrochemical parameters were documented to illustrate the bio-electrochemical characteristics of SMFC-c and P-SMFC-c. Removal pathways of NO3− in different treatments were studied by adding quantitative 15NO3− to water column. The results showed that the cathodic reaction in SMFC-c was mainly catalyzed by aerobic organisms attached on the cathode, including algae, Pseudomonas, Bacillus, and Albidiferax. The oxygen secreted by plants significantly improved the power generation of SMFC-c. Both electrogenesis and plants enhanced the complete removal of NO3− from the sediment–water system. The complete removal rates of added 15N increased by 17.6% and 10.2% for SMFC-c and plant, respectively, when compared with control at the end of experiment. The electrochemical/heterotrophic and aerobic denitrification on cathodes mainly drove the higher reduction of NO3− in SMFC-c and plant, respectively. The coexistence of electrogenesis and plants further increased the complete removal of NO3− with a rate of 23.1%. The heterotrophic and aerobic denitrifications were simultaneously promoted with a highest abundance of Flavobacterium, Bacillus, Geobacter, Pseudomonas, Rhodobacter, and Arenimonas on the cathode.