Constructed Wetland in a Compact Rural Domestic Wastewater Treatment System for Nutrient Removal

摘要

Direct discharge of scattered rural sewage into surface water bodies with no efficient and economic treatment processes is one of the main reasons for the deteriorative aquatic environment in China. In this study, a simplified pilot-scale rural wastewater treatment system has been proposed. The system consisted of an anaerobic digestion tank (for organic substances pretreatment), an aerobic five-cell submerged biofilm reactor (for organic substances degradation), and a constructed wetland (CW; for nutrients removal and effluent quality control) in sequence. A five-step water-dropping aeration technique was incorporated in the biofilm reactor for oxygen replenishment with one pump, the only equipment applied in the system that involved in water elevation and effectively alleviated the oxygen stress in the CW for nutrient removal improvement. Effects of economic vegetation species (water spinach vs. water bamboo), packing media (coal cinder vs. gravel), and flow patterns (submerged horizontal flow vs. vertical flow) on CW performance were examined under continuous influent loading. Distributions of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria (generally accumulated in the top [≤20 cm] front part of the CW), and denitrifying bacteria (mainly in the deeper part [>20 cm] of the CW) were explored for total nitrogen (TN) removal. The optimized system achieved 68.9%±15.8%, 68.6%±15.1%, 69.5%±14.6%, and 86.3%±12.2% of chemical oxygen demand, NH4+-N, TN, and total phosphorus (TP) removal efficiencies, respectively, during a 6-month operation with the effluent meeting the Chinese sewage discharge standard and were indicated to be of low cost, operation-friendly, and applicable for sewage treatment in Chinese rural communities.