Study On Treatment Of Polluted River Water Using Pilot-scale Constructed Wetlands

Study on treatment of polluted river water from Xinyi River using pilot-scale Constructed Wetland (CW) was performed. This river is a flood discharge river with great variations of water quantity and quality. The feasibility of using CW to treat the polluted river was demonstrated. The effluent water quality and removal efficiency of different CW systems at different time periods, different retention times, different pollutant loads, and different aquatic plants were compared.The main results show that:(1) CW has good efficiencies to improve the water quality of polluted Xinyi River and the effluents reach the targeted water quality. It is a practical measure for polluted river water treatment. (2) Among the selected plants in the CWs, Typha latifolia, Scirpus locustris, Canna glauca and Lythrum salicaria, the former three can resist inundation. (3) When the influent concentrations of COD_Mn, NH₄⁺-N and colourity were 3.11-117.28 mg/L, 1.30²4.71mg/L and 45-600, their mean removal rates were 59.90%, 85.50% and 65.00% of SSFW, 77.82%, 86.988% and 77.50% of IVFW. The efficiency of pollutant removal of IVFW is better than that of SSFW. (4) Except the first stage of experiment, the removal efficiencies of COD_Mn and NH₄⁺-N of SSFW and IVFW were the highest during April to June. During October to December, the removal efficiencies of both systems were relatively low. (5) IVFW system has better resistance to pollutant impact load than SSFW system. The optimal pollutant load of COD_Mn for both systems is 8—12 g/m².d. When it is too low or too high, the removal rate decreases. (6) The best retention times of COD_Mn and NH₄⁺-N of SSFW are 2 and 2.5 days respectively, and 1.5 and 2 days for IVFW system respectively. (7) The systems can be kept at stable temperature and have strong reaeration ability. The pH of influent is 6.4-8.0, which is a good condition for nitrogen removal in CW. (8) Four types of SFW with different aquatic plants have different removal rates of COD_Mn, NH₄⁺-N and colourity. In terms of COD_Mn, Typha latifolia has the best removal efficiency, and then Canna glauca, Scirpus locustris, and Lythrum salicaria (pollutant removal efficiencies from high to low). For NH₄⁺-N, Canna glauca is the best one, and then Lythrum salicaria, Typha latifolia, Scirpus locustris . While for colourity, Canna glauca is the best one, and then Typha latifolia, Scirpus locustris,Lythrum salicaria. Generally, compared with the four different aquatic plants, Typha latifolia and Canna glauca have stronger ability for purifying pollutants.