Reshaped structure of microbial community within a subsurface flow constructed wetland response to the increased water temperature: Improving low-temperature performance by coupling of water-source heat pump

Abstract

To evaluate the pollutant removal mechanisms and pathways in traditional constructed wetlands (CWs), and remove its operation bottleneck under low temperature, a co-system was established by coupling a subsurface flow constructed wetland (SFCW) and the water-source heat pump (WSHP) units. Experimental consequence demonstrated that the water temperature had increased significantly, and the mean temperature of influent was 8 ± 3 °C while that of effluent was 15 ± 5 °C. High average removal efficiencies of COD (64.5%), NH3-N (89.5%), NO3-N (90.2%), TN (58%), and TP (93.5%) were achieved in the experimental co-system. Optimal removal efficiency was achieved when pH was 6–7.5 and hydraulic retention time (HRT) was 4 days. Nitrification led to the higher organic pollutants removal efficiency. Meanwhile, it was considered to be due to the significant variation of the microbial community structure after the application of the WSHP units, in which the species richness and community equitability significantly improved. The thermophilic communities grew and reproduced in large numbers. The results also showed the application of co-system was an effective and sustainable strategy for removing diverse pollutants in cold climate.