Abstract
An integrated vertical-flow constructed wetland-microbial fuel cell system (CW-MFC), consisting of an up-flow chamber and a down-flow chamber, was constructed to treat synthetic sewage wastewater. The performance of CW-MFCs filled with different substrates [i.e., ceramsite (CM-A), quartz (CM-B), and zeolite (CM-C) granules] under various hydraulic retention times (HRTs, 7.6, 4.0, and 2.8 d) was evaluated. Efficient and stable nitrogen (N) and phosphorus (P) removals were observed in CM-A under different HRTs, while the voltage outputs of the CW-MFCs was greatly reduced as the HRTs decreased. With an HRT of 2.8 d, the ammonium (NH4+-N) and orthophosphate (PO43–-P) removal efficiencies in CM-A were as high as 93.8 and 99.6%, respectively. Bacterial community analysis indicates that the N removal in the cathode area of CM-A could potentially benefit from the appearance of nitrifying bacteria (e.g., Nitrosomonas and Nitrospira) and relatively high abundance of denitrifiers involved in simultaneous nitrification and denitrification (e.g., Hydrogenophaga, Zoogloea, and Dechloromonas) and denitrifying sulfide removal (e.g., Thauera). Additionally, the difference in N removal efficiency among the CW-MFCs could be partly explained by higher iron (Fe) content in milled ceramsite granules and higher abundance of denitrifiers with nitrate reduction and ferrous ions oxidation capabilities in CM-A compared with that in CM-B and CM-C. Efficient PO43–-P removal in CM-A was mainly ascribed to substrate adsorption and denitrifying phosphorus (P) removal. Concerning the substantial purification performance in CM-A, ceramsite granules could be used to improve the nutrient removal efficiency in integrated vertical-flow CW-MFC.
Highlights
Water eutrophication caused by the enrichment of nitrogen (N) and phosphorus (P) has become a worldwide environmental problem in recent years
As the HRT decreased from 7.6 to 2.8 d, increased NH4+-N concentrations were observed in the sampling ports of the up-flow chamber of CM-A, the down-flow chamber of CM-B, and both chambers in CM-C
The results indicated that the NH4+-N removal from layer U4 to U2 might be associated with the substrates selected
Summary
Water eutrophication caused by the enrichment of nitrogen (N) and phosphorus (P) has become a worldwide environmental problem in recent years. Constructed wetlands (CWs) have been widely accepted as a preferable alternative for wastewater treatment because of their low initial investment costs, easy operation and maintenance, and good landscape integration. The integration of CWs with microbial fuel cells (i.e., constructed wetlandmicrobial fuel cell system, CW-MFCs) has attracted worldwide attention (Doherty et al, 2015). The efficiency of power generation and wastewater treatment is the focus of CW-MFC research. Concerning research on power generation, great efforts have been made to increase power density (Shen et al, 2018; Xu et al, 2019), though the usefulness of CW-MFCs system as an electricity generating device in real scenario has not yet been well examined. For research on wastewater treatment, attention has been extended from chemical oxygen demand (COD) removal to N removal (Xu et al, 2018)
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