The Efficiency of Constructed Wetland to Treat Primary Sewage Effluent Under Different Operational Conditions

The efficiency of constructed wetland to treat weak and medium primary sewage effluent was tested under three rates of sewage inflow and two types of growing plants (i.e., leaf cattail and common reed). The capability of the wetland to remove COD, BOD, TSS, TDS and F. coliform from the primary weak sewage increased with decreasing the rate of the sewage inflow from 12 L/hr. to 6L/hr., with little or no further changes at a rate of 3 L/hr. The two plants (Leaf cattail and common reed) were equally effective in sewage purification. Levels of either COD, BOD or TSS in the treated primary weak sewage at all rates of sewage inflow and numbers of F. coliform in the sewage treated only at the 6 and 3 l/hr rates of inflow fulfill the requirements of the guidelines for the use of wastewater in agriculture. The capability of the wetland to remove BOD and COD decreased with increasing the strength of the primary sewage. At any given rate of inflow, the percent removal of BOD and COD from the medium sewage was less than that from the weak one. This decrease in the capability was much more observed for BOD removal than COD removal. The reduced ability of the wetlands to control high BOD/COD levels in the medium sewage system is thought to be that there is not enough oxygen in the system to do its job.