Design and operation of an eco-system for municipal wastewater treatment and utilization

An eco-system consisting of integrated ponds and constructed wetland systems is employed in Dongying City, Shandong Province for the treatment and utilization of municipal wastewater with design capacity of 100,000 m³/d. The total capital cost of this system is 680 Yuan (RMB) or US$82/m³/d, or about half that of the conventional system based on activated sludge process, and the O/M cost is 0.1 Yuan (RMB) or US$ 0.012/m³, only one fifth that of conventional treatment systems. The performance of the wastewater treatment and utilization eco-system is quite good with a final effluent COD, BOD, SS, NH₃-N and TP of 45–65 mg/l, 7–32 mg/l, 12–35 mg/l, 2–13 mg/l and 0.2–1.8 mg/l respectively and the annual average removals of COD, BOD, SS, NH₃-N and TP are 69.1%, 78.3%, 76.4%, 62.1% and 52.9% respectively, which is much better than that of conventional pond system or constructed wetland used separately and illustrates that the artificial and integrated eco-system is more effective and efficient than the simple natural eco-system.