Performance of a combined eco-system of ponds and constructed wetlands for wastewater reclamation and reuse

An on-site study on the operational performance of a combined eco-system of ponds and SF constructed wetland for municipal wastewater treatment and reclamation/reuse in Donging City, Shandong, China was carried out from January 2001 through October 2003. The removal efficiencies for various main parameters were: TSS 84.8±7.3%, BOD₅ 87.2±5.3%, COD_Cr 70.2±18.6%, TP 52.3±23.1%, and NH₃-N 54.8±23.9% with effluent concentration of TSS 9.12±5.12 mg/l, BOD₅ 6.44±4.58 mg/l, COD_Cr 42.8±6.7 mg/l, TP 0.94±0.27 mg/l and NH₃-N 7.95±2.36 mg/l. In addition, the removal efficiencies for faecal coliforms and total bacteria were >99.97% and >99.998% respectively, which well meet Chinese National standards for effluent quality of municipal wastewater treatment plants. The composition of TSS was closely related to COD_Cr and BOD₅ variations, and nitrification-denitrification is the major mechanism of nitrogen removal both in ponds and in wetlands. In addition, sedimentation also played an important role in the removal of TSS, nitrogen, phosphorus and BOD₅. The removal efficiencies of various parameters, the number of species and biomass of biological community in the system increased gradually with the ecological maturation.