Biological Treatment of Leachate Using Sequencing Batch Reactor

Abstract

In Sri Lanka municipal solid waste is generally disposed in poorly managed open dumpswhich lack liner systems and leachate collection systems. Rain water percolates through thewaste layers to produce leachate which drains in to ground water and finally to nearby waterbodies, degrading the quality of water. Leachate thus has become a major environmentalconcern in municipal waste management and treatment of leachate is a major challenge forthe existing and proposed landfill sites.The study was conducted to assess the feasibility of the usage of the Sequencing BatchReactor in the treatment of the landfill leachate up to the proposed levels in the draft report of“Proposed Sri Lankan standard for landfill leachate to be disposed to the inland waters".Leachate collected from the open dumpsite at Meethotamulla, Western Province, Sri Lankawas used for leachate characterization.SBR was constructed with a 10-liter working volume operated in an 18 hour (h) cycle modeand each cycle consists of 15 h of aerobic, 2 h settle and 0.5 h of fill/decant stages. TheDissolved Oxygen level within the SBR was maintained at 2 mg/l through the aerobic stage.Infeed was diluted with water during the acclimatization period and a leachate to water ratioof 55:45 was maintained. The removal efficiencies for different parameters were; COD(90.5%), BOD (92.6%), TS (92.1%), Conductivity (83.9%), Alkalinity (97.4%), Hardness(82.2%), Mg (80.5%), Fe (94.2%), Zn (63.4%), Cr (31.69%), Pb (99.6%), Sulphate (98.9%),and Phosphorus (71.4%) respectively. In addition Ni and Cd were removed completelyduring a single SBR cycle.Thus the dilution of leachate in the dumpsites using municipal wastewater, groundwater orrainwater was identified as the most cost effective dilution methods. The effluent from theSequencing batch reactor is proposed to be further treated using a constructed wetland beforereleasing to surface water.