Nitrogen and phosphorus removal in microbial fuel cell-constructed wetland integrated with layered double hydroxides coated filter for treating low carbon wastewater

To further improve nitrogen and phosphorus removal from secondary effluents, the microbial fuel cell - constructed wetland (MFC-CW) was integrated with a filter reactor (FR). MgAl-layered double hydroxides (MgAlLDHs) and MgFe-LDHs were utilized to modify the activated carbon and applied in the integrated system. The phosphate adsorption capacity of the modified substrates was compared. Meanwhile, the pollutants removals and bioelectricity generation with LDHs modified substrates addition in MFC-CW-FR were investigated. Results indicated that the adsorption of phosphate by LDHs-modified substrates mainly occurred through ion exchange, electrostatic adsorption, and chemical complexation. MgAl-LDHs modified activated carbon showed better phosphate adsorption capacity, with the total phosphorus (TP) and total nitrogen (TN) removals of 43.55 % and 21.72 % in FR, respectively. Compared to the addition in the cathode region of MFC-CW, MgAl-LDHs modified activated carbon was more suitable to be added in FR, with the effluent TP and TN concentrations below 0.20 and 5.50 mg/L. Besides, the output voltage could be maintained at 0.8 V. LDHs modified substrates addition also enriched the microbial community, with higher abundances of denitrifying bacteria and phosphate accumulating organisms (PAOs). In summary, LDHs modified substrates contributed to the simultaneous nitrogen and phosphorus removal and provided a novel method for the deep treatment of secondary effluents.