Study Of Multi-stage Constructed Wetland For Wastewater Treatment

In this paper, the technical design of a small-scale surface-flow constructed wetland (SFCW) was described. As the conventional SFCW has always problem when it runs in cold climate area, some changes were made with the structure of the SFCW. Depths of the wetland was increased in order to form an anoxic area in the reactor, consequently the requirement of area for one constructed wetland can be reduced. The new substrate, ceramic pellet, instead of soil was used as filling material to support the growth of plants and microbes. The whole SFCW system was consists of three reactors. Wastewater was pumped to the first reactor and flowed to the other two reactors by gravity. Artificial domestic wastewater was made and treated with this SFCW, the performance of Nitrogen, COD, BOD, and Phosphorus removal was examined. Influents with different concentrations were investigated.Influent with low concentration was treated in experiment I, and with higher concentration in experiment II. Results showed that the average removal efficiencies (from both experiments) of COD were 90.5% and 93.7%, respectively. The reductions of TN were 84.3%, 72.8%, respectively. The mean removal rates of PO43- were 92.2%, 95.7%, and removal rates of TP were 90.0% and 95.8%.The role of plant existed in the reactor was investigated by using a non-planted reactor as comparison. The removal efficiencies of COD were 53.5% and 72.9%, respectively, in the non-planted and planted reactors. While, the reductions of TN were 32.7% and 53.4%, the removal rates of TP were 43.9% and 74.8%, and the decreases of PO43- were 49.5%, 86.7% respectively. Results indicate that plants existing in the treatment system can enhance the performance of a SFCW.In order to gain more experiences, the water flow direction was changed from surface to vertical flow, and forming a vertical subsurface flow system (VSCW). The same influent was investigated again and no significant difference was found between VSCW and SFCW. Except a slightly increase of COD removal efficiency was found. The average removal rates of COD, TN, TP and PO43- were 95,2%, 68.4%, 96.3% and 95.0%.During these experiments, it is evident that the treatment efficiency was affected by the ambient temperature. Nevertheless, during the wintertime, the SFCW system kept a reasonable treatment performance.