ASSESSMENT OF POLLUTION OF THE RIVER BURIGANGA, BANGLADESH, USING A WATER QUALITY MODEL

Constructed wetland systems are used to treat domestic and industrial wastewater and agricultural runoff. In this field study the influence of hydraulic loading, retention time, water column depth and phosphorus (P) concentrations of influent wastewater on P and nitrogen (N) removal was examined in experimental constructed wetland systems. Five constructed wetlands with a surface area of 150 m^2, were developed in the field. Results showed that P concentrations of water from outlets of all five systems decreased (from as low as 11% decrease for the system which received wastewater with average P concentration of 8.2 mg P L^-1 to as high as 48.9% decrease for the system which received wastewater with average P concentration of 3.58 mg P L^-1) compared to the influent water. The N concentrations in the outlet water were also decreased in all five systems (from as low as 26.3% decrease to as high as 77.5% decrease) compared to the influent water. The total P and N in the wetland sediment increased in the first year in all five systems but were unchanged at the end of the second year. The study showed that low hydraulic loading and greater retention times positively enhanced removal of P and N from wastewater in constructed wetland systems.