Treatment of Rural Domestic Sewage by Combined Technology of Upflow Anaerobic Sludge Blanket and Two-stage Constructed Wetlands

To develop decentralized sewage treatment devices suitable for rural areas in China, a combined technology of upflow anaerobic sludge blanket (UASB) and two-stage surface flow constructed wetlands (FWS1, FWS2) was applied to treat rural domestic sewage. The experiment was divided into four stages according to different hydraulic retention time (HRT) of sewage passing through the UASB, and the removal effect of COD, BOD₅, NH₄⁺-N, TN, TP and SS was explored. When the HRTs of UASB, FWS1 and FWS2 were 2 h, 45 h and 64 h, respectively, the comprehensive treatment efficiency of the whole system was the best, and the removal rates of COD, BOD₅, SS, NH₄⁺-N,TN and TP were 88%, 96%, 90%, 77%, 72% and 98%, respectively. It was found that the removal efficiencies of COD, BOD₅ and SS decreased with the shortening of HRT of UASB. The degradation of NH₄⁺-N and TN mainly relied on the plant transformation and biological nitrification and denitrification of the wetland system. Both UASB and constructed wetlands played an important role in the TP removal. The first order reaction rate constants (K_V) of COD, BOD₅, SS, TP, NH₄⁺-N and TN were calculated by using the firstª²order reaction kinetics, which were (0.23¡À0.09) d^-1, (0.22¡À0.03) d^-1,(0.18¡À0.09) d^-1, (0.25¡À0.09) d^-1, (0.09¡À0.03) d^-1 and (0.11¡À0.03) d^-1, and the relationship between the first-order reaction rate constant and water temperature was constructed.