Although there have been many studies on the process conditions of Constructed Wetlands (CW) and Microbial Fuel Cells (MFC), there are few studies on the Constructed Wetlands coupled with Microbial Fuel Cells. Currently, low power production is the main problem faced by Constructed Wetlands-Microbial Fuel Cell systems (CW-MFCs). This experiment intends to research the effects of HRT, influent COD and electrode spacing on wastewater treatment and power generation performance. In this experiment, CW-MFCs with two different electrode spacings (18 cm for reactor A and 28 cm for reactor B) were set up under continuous flow conditions. The effects of HRT, influent COD and eletrode spacing on wastewater treatment and power generation performance were explored using a single-factor controlled variable method. Experiment results showed that the extension of HRT was beneficial for contaminants removal and the power generation of the CW-MFCs, but the excessive extension was ineffective for the electricity output. The optimal HRT of the CW-MFCs was 24 h when influent COD was 500 mg·l-1. Improving influent COD within the appropriate range (500~1000 mg·l-1) facilitated the power generation and contaminant removal performance of the CW-MFCs. The maximum output voltage and power density were obtained in reactor A when influent COD was 1000 mg·l-1 and HRT was 24 h, which were 548 mV and 120 mW·m-3, respectively. Compared with reactor B, reactor with smaller electrode spacing achieved better electricity generation and contaminant degradation under the optimal condition. Its average output voltage could be improved by 5.1~46.1% and the removal rates of COD and NH4 +-N could also be improved by 0.2~4.9 % and -0.9~13.7 %, respectively. This phenomenon indicates that there was a significant positive correlation between the number of Gram-negative bacteria and the electricity production performance of the CW-MFCs, which was due to the difference in electron transfer efficiency. This study can provide operation parameters for the CW-MFCs process.

Although constructed wetlands (CWs) are widely used around the world with various substrates, the mechanisms of how these modified substrates affect wastewater treatment are still unknown. In this study, CW microcosms were established with and without ceramsite as a substrate, and the wastewater treatment efficiencies were evaluated during 71 days of incubation. Using the 16S rRNA high-through sequencing, the mechanisms of how CW substrate changed the microbial community was quantified. The results showed that compared to soil as substrate, the use of ceramsite as substrate material enhanced the removal of pollutants from CW systems, particularly under a short retention time (1.5-day) condition. There were more beneficial microorganism groups (nitrogen, sulfur, phosphate) in the ceramsite CW system than the non-ceramsite CW system, particularly in the bottom layers. Moreover, the CW with ceramsite substrate had more nitrification function. All of these results suggested that the ceramsite CW system enhanced the removal of pollutants because it increased the concentration of key microbes that are necessarily for nutrient cycles.

In this study, homemade ceramsite-soil filler (system A) and a simple soil filler (system B) were applied in vertical upflow constructed wetlands, and their performance in the treatment of rural domestic wastewater were investigated under various HRTs and packing heights. Optimum performance was reached at a HRT of 6.4 d in both systems. The average removal rates of ammonia nitrogen (NH4 +-N), total nitrogen (TN), and total phosphorus (TP) in system A were as high as 90.78, 86.04, and 90.15%, respectively, which were 0.94, 2.21, and 10.62% higher than those in system B. The TN and NH4 +-N removal efficiencies of both systems decreased with shorter HRTs, whereas the TP removal efficiency was almost not affected. Along the inlet direction, with increasing packing height, the pollutant removal capacity gradually decreased, and the NH4 +-N removal efficiencies in the bottom layers (0-145 mm) of system A and B were 55.88 and 50.22%, respectively, with NH4 +-N volumetric loads of 8.63 and 7.76 g/(m3·d). System A contained more nitrifying genera at the genus level, mainly including Stenotrophomonas, Sphingomonas, and Acinetobacter. The addition of ceramsite resulted in a higher treatment efficiency and resistance to hydraulic shock loading.