Advanced Treatment Of Domestic Sewage With A Constructed Wetland In North China

In this paper, a small pilot plant of multi-stage constructed wetland (CW) is described. The whole experiment consists of three tank. Compared to the traditional constructed wetlands, the depth of the CW is increased in order to form an anaerobic region, which is similar to the anaerobic pre-treatment of wetland system.At the same time, the use of lightweight ceramic also avoid the blocking of soil substrate, and also can increase the surface area for microbial activities. Meanwhile, the improvement on the structure of the reactor changes the hydrodynamics by changing the flow direction under the existing circumstances. This increase the capacity and economical efficiency in treating various type of Wastewater.The performance of the CW and a control system (without plant) were investigated outdoor in Dalian to treat the effluent from a municipal Wastewater treatment plant (with secondary treatment). The whole experiment consists of four stages. The first phase was setting up stage, the environment for the growth of microorganisms was improved, and the growth of plants was monitored regularly. The second phase was the HRT 3 days stage. In this period, parameters including COD, TN, NH₃-N, NO₂-N and TP removal efficiencies were 75%,75%,95%,75% and 50%, respectively, which were 10%,30%,30%,20% and 50% higher compared with the control system. The third phase was the HRT 2 days stage. In this stage the COD, TN, NH₃-N, NO₂-N and TP removal efficiency were 85%, 75%,100%,70% and 98%, respectively, which were 10%,20%,35%,25% and 63% higher compared with the control system. The fourth stage was intermittent operation period. In this stage, influent was pumped into the first tank at the same flow rate as the third phases, while operation method was different. Every three days, the tank will be emptied for one day. The results were compared with the continual operation phase so as to investigate the influences of operation mode. Results indicated that plants contributed much to the removal of pollutants, and the CW system was a practical alternative for removing N and P from discharge of municipal Wastewater treatment plant, which is significant for improving water quality and mitigating of eutrophication problem.