Performance of an intensive pond system treating municipal wastewater in a cold region

A full-scale intensive pond system (IPS) with shorter HRT was designed, constructed and operated in Jining, Inner-Mongolia for the treatment of municipal wastewater, which is a mixed domestic and industrial wastewater characterized by quite high SS and lower BOD5/COD ratio values or lower biodegradability. Therefore, the pond system was designed as an integrated intensive pond system (IIPS) consisting of settling/anaerobic pond (SAP), intensified anaerobic pond (IAP), facultative pond (FP), and polishing ponds (PPs). In order to improve the performance of the IPS, some intensified measures were made, including inlet and outlet even-distribution systems of each unit pond, package of biofilm carrier in IAP for the increase and even distribution of biomass; overflow waterfalls on the dikes between unit ponds for the increase of DO in pond water, gravel filtration dike (or dam) for removing suspended solids including algae, which have improved the performance of the IPS remarkably in terms of removal of main pollutants, such as SS, COD, BOD5, TN, NH3-N, TP and total bacteria. The final effluent from the IPS in warm seasons from May to October were SS 7.2-10.8 mg/L, BOD5 8.5-19.6 mg/L, COD 44.1 - 76.5 mg/L, and NH3-N 1.5-10.2 mg/L, which well meet Chinese national discharge standard (2nd class) of secondary municipal wastewater treatment plants, i.e. BOD5 and SS 30 mg/L respectively, COD 100 mg/L, and NH3-N 25 mg/L.