Performance of papyrus based batch loaded vertical subsurface flow constructed wetland mesocosms in Kampala, Uganda

Abstract

The performance of batch loaded vertical subsurface flow constructed wetland mesocosms planted with Cyperus papyrus, with regard to treatment of secondary pretreated municipal wastewater in Kampala, Uganda was investigated. The study was aimed at assessing the performance of these constructed wetland systems with or without papyrus under batch loading mode, with the specific objectives; 1) To assess the influence of papyrus vegetation on the hydrology of the VSSF CW system; 2) to determine the organic matter removal efficiency of the VSSF CWs; 30 to determine the nitrogen and phosphorus removal efficiency of the VSSF CWs. On site measurements for pH, Dissolved Oxgen, Electrical Conductivity and temperature (using portable meters) and laboratory analyses were conducted weekly over a fourteen week period following bio-film establishment and the key parameters investigated were precipitation and evapo-transpiration, Biochemical oxygen demand (BOD5), Chemical oxygen demand (COD), ammonium-nitrogen (NH4-P) and Total phosphorous TP removal. The nutrients were all determined according to standard methods (APHA, 1995(. The mean evapo-transpiration ranged from 16.5-17.8mm/day in the planned mesocosms over the study period. The results obtained also showed impressive organic matter removal efficiencies i.e., BOD5: 82.9% (controls) and 83.52% (planted units) and COD: 75.59%) controls) and 77.03% (planted treatments). Average N and P removal efficiencies were also high with 81.3% and 87% for NH4-N in unplanted and planted units respectively, TN:70.36% (controls) and 97% (planted), TSS: 87.2% (controls) and 86.32% (planted). Overall, increased NO3-N concentration values were obtained in the influent compared to the influent in all the four CW units and so the percentage removal efficiencies for these N species were not significant. It can therefore be conclude, from this study, that batch loaded VSSF CWs are very efficient as regards removal of organic matter, N and P from secondary pre-treated wastewater and more research studies are recommended to investigate the performance these CWs with other tropical macrophytes and under different operation modes.