Assessment of water quality of Sembilang River receiving effluent from controlled municipal solid waste (MSW) landfill in Selangor

Most of the landfills in Malaysia are situated near to the main river basin that supplies almost 90% of water requirement. This includes landfills in Selangor where a total of 20 landfill sites are situated in 5 main river basins and the highest number of operating landfills (three) are at the Selangor River Basin (Jeram, Bukit Tagar and Kuang Inert landfills). This situation has caused wide concern over the water safety, even the leachate has been treated. The leachate itself still contains contaminants that are difficult to treat. The main objective of this study is to investigate the effect on water quality of Sembilang River that receives effluent from the nearby landfill. In this study, we analyzed samples of water from ten sampling stations starting from the upstream to downstream of Sembilang River. The water quality was evaluated by the Water Quality Index (WQI) depending on in-situ and laboratory analysis. 11 water quality variables are selected for the quality assessment; temperature, pH, turbidity, salinity, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, total suspended solid, ammoniacal nitrogen, phosphate and nitrate. The result indicated that, when the effluent mixed with the river water, the water quality decreased gradually and was found to be lower at a few stations. The water quality of Sembilang River falls under Class III of Water Quality Index with ranges between 68.03 to 43.46 mg/L. It is revealed that the present scenario of water quality of Sembilang River is due to the effect of effluent from the landfill.