Evaluation of Leachate Treatment System at Gohagoda Dumpsite

Abstract

Leachate management is one of the major concerns in the rehabilitation efforts of the Gohagoda dumpsite. Leachate collection network was designed after detailed investigation of leachate generation points of the dumpsite and drainage pattern. Interceptor leachate drains was laid on the periphery of the dumpsite to capture all subsurface flows in the upper strata that normally discharge into surface flow stream s at different point in the dumpsite. A leachate treatment bioreactor (LTB) and constructed wetlands (CW) and a subsurface charcoal filter bed were constructed to treat the leachate collected from the dumpsite. This paper is aimed to evaluate the performances of existing leachate treatm ent system and compare the results with the previous studies on leachate quality of the dumpsite. Before commencement of rehabilitation of the dumpsite, the biochemical oxygen demand (BOD) value reported was 7,500m gL1 and average chemical oxygen demand (COD) value was 33,900± 14,100m g L '. The drastic reduction of treatment parameters at the inlet to the LTB, like BOD and COD of 367.5+237m gL 'and l,905±l,092m g L ' respectively nullified the performance of it. In fact sometimes, the LTB performances were negative for conductivity, salinity, BOD and TDS, indicating washing out of ions. Nevertheless, in spite of higher influent concentrations than the designed values for the CW, the removal efficiencies of BOD and COD were over 67% and 31% , respectively. Therefore, incorporation of an activated sludge process (ASP) and algal pond after the LTB could reduce the influent parameters, thus improve removal efficiency of the CW to meet the desired discharge standards.