Evaluation of the optimization effect of a combined constructed wetland with micro-polluted water sources

Abstract

The research aimed to evaluate the eight-years purification performance of a large-scale combined constructed wetland (CW) improving micro-polluted water, to analyze problems occurring during long term operation and their causes, as well as to propose measures and suggestions for further optimization. The results shows that the average removal rates (RRs) of permanganate index (CODMn), ammonia nitrogen (NH4+-N), total nitrogen (TN) and total phosphorus (TP) were 4.39 % ± 12.64 %, 41.57 % ± 16.36 %, 32.61 % ± 23.36 % and 47.05 % ± 20.39 % during 2013–2020, respectively. Compared with other similar constructed wetlands, the removal rate of each pollution indicator was relatively low. The deep purification zone exhibited the best performance due to the long hydraulic retention time (HRT); the pretreatment zone had low capacity in removal of CODMn and TN; the emergent plant zone was significantly affected by the plant arrangement; the purification performance of submerged plant zone in the first three years was inefficient due to the difficult restore of submerged plants. The average RRs for CODMn, NH4+-N, TN, and TP after the optimization engineering were 2.54 ± 14.76 %, 39.62 ± 18.47 %, 31.86 ± 22.19 %, and 46.06 ± 21.02 %, respectively, indicating that the overall purification performance was not improved significantly. The analysis shows that influent concentrations, temperature, HRT and design of combined processes were key factors influencing the purification performance of CW. In the future, it is necessary to take targeted measures for the above key factors to improve the water quantity and quality assurance rate of drinking water sources, to ensure the drinking water health and safety.