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Photovoltaic electrolysis improves nitrogen and phosphorus removals of biochar-amended constructed wetlands
- Gao, Yan, Yan, Cheng, Wei, Ruping, Zhang, Wen, Shen, Jianing, Wang, Mingxuan, Gao, Bin, Yang, Yicheng, Yang, Liuyan
- Ecological engineering 2019 v.138 pp. 71-78
- adsorption, ammonium nitrogen, anodes, biochar, cathodes, chemical precipitation, constructed wetlands, electrochemistry, electrolysis, energy flow, flocculation, hydrogen-oxidizing bacteria, ions, iron, nitrate nitrogen, nitrogen, phosphates, solar energy, wastewater treatment
- To deeply remove nitrogen (N) and phosphorus (P) from constructed wetlands (CWs), the authors found that CWs can be combined with the use of photovoltaic energy for best results. Thus, electrolysis-integrated, biochar-amended, horizontal (subsurface)-flow-constructed wetlands (E-BHFCWs) were combined with free-water, surface-constructed wetlands (FWSCWs) to remove N and P from secondary effluent water of a wastewater treatment plant (WWTP). Photovoltaic energy was used for electrolysis to intensify the removal of nitrate nitrogen (NO3−-N), ammonium nitrogen (NH3-N), and phosphate phosphorus (PO43−-P) in E-BHFCWs. In addition, FWSCWs were constructed to further remove NO3−-N, NH3-N, PO43−-P and iron ions in effluent of E-BHFCWs and to enhance DO concentration. For the E-BHFCWs combined with FWSCWs, the removal rates of NO3−-N, NH3-N, and PO43−-P were 73.28%, 53.11% and 67.58% respectively. The removal amounts of NO3−-N, NH3-N, and PO43−-P were about 211.08 kg N/a, 64.81 kg N/a and 10.46 kg P/a by E-BHFCWs. Photovoltaic electrolysis in E-BHFCWs was able to enhance NO3−-N removal through electrochemical reduction by iron cathodes, enriched hydrogenotrophic bacteria in the substrate, and by modified biochar substrate in situ with iron ions. Meanwhile, NH3-N was mainly removed by modified biochar adsorption, nitrifying microbes, and plant uptake. The removal rate of PO43−-P was also enhanced due to the formation of ferric ions by the anodization of sacrificial iron anodes, causing chemical precipitation, physical adsorption, and flocculation of PO43−-P. Thus, E-BHFCWs combined with FWSCWs are capable of effectively promoting removals of NO3−-N, NH3-N, and PO43−–P and provide a new insight into a new energy flow that can enhance N and P removals of CWs.