Performance of integrated vertical-flow constructed wetland-microbial fuel cells during long-term operation: The contribution of substrate type and vegetation

An integrated vertical-flow constructed wetland-microbial fuel cell (CW-MFC) system, consisting of an upflow chamber and a downflow chamber, was designed to treat synthetic sewage wastewater. The potential influence of vegetation (with and without the planting of Canna indica) and substrate type (ceramsite, quartz and zeolite granules filled in CM-A, CM-B and CM-C, respectively) on the performance of wastewater treatment and electricity generation in the CW-MFCs was evaluated during long-term operation. A two-way analysis of variance (ANOVA) indicated that both vegetation and substrate type significantly affected the effluent ammonium (NH4+-N) and orthophosphate (PO43--P) concentrations (p < 0.05), and the interaction term (i.e., vegetation × substrate type) was significant for both NH4+-N and PO43--P removal (p < 0.05). The efficient N removal in the planted CM-A and CM-C could be partly attributed to the enhanced cathodic denitrification in association with the high-power outputs. After plant removal, the deterioration of wastewater treatment and electricity generation performance was observed in all of the CW-MFCs except for CM-A. Using ceramsite as the substrate of a CW-MFC would contribute to a promising performance. However, the increased nirK/nirS and nosZ/16 S rDNA ratios indicated a risk of N2O emission in the unplanted CM-A, while the gradual decrease in the PO43--P removal efficiency indicated the saturation of adsorption sites on the ceramsite granules after two years of operation.