Development and Performance Evaluation of the Leachate Treatment System at Gohagoda Municipal Solid Waste Disposal Site

Abstract

A private company with technical support of University of Peradeniya has undertaken the task of rehabilitating the Gohagoda dumpsite. Not all of the leachate collection system (LTS) is completed yet and runoff water too gets mixed with the leachate on one side of the dumpsite. The LTS consisting of leachate collection tanks, a leachate treatment bioreactor(LTB) followed by an algae pond(AP), a floating wetland(FW), two sub-surface constructed wetlands(SCWs), two charcoal filter-beds(CFBs). LTSoutlet is being discharged into a natural stream (NS). In this research, the existing LTS was improved and the performances were evaluated. To determine the surface water quality of surrounding area and performance of the LTS, samples were obtained from 13 pre-defined points on weekly basis for two months, analysed for 14 quality parameters. Average pH, dissolved oxygen (DO), chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of inlet leachate to the LTS were 7.74±0.35, 0.46±0.5mg/L, 24,552±2,612mg/L and 4,125±965mg/L respectively. LTSoutlet of pH (7.16±0.23) was within the Central Environmental Authority water quality discharge standards. Average salinity, EC, DO, TDS, TSS, TS, VS, VSS, BOD, COD, PO4 -3, NO3 - and NH4 +of LTSoutlet were 0.84±0.25%0, 1.71±0.52mS, 0.63±0.6mg/L, 852±261mg/L, 1,058±199mg/L, 1,303±772mg/L, 406±220mg/L, 609±111mg/L, 217±177mg/L, 780±1,049mg/L, 2.33±3.29mg/L, 0.97±0.27mg/L, 4.38±1.59mg/L respectively. Average pH, TDS, BOD, PO4 -3 and NO3 - and NH4 + of NSoutlet were 7.69±0.39, 1,457±930mg/L, 1,382±784mg/L, 5.04±6.36mg/L, 1.58±1.26mg/L, 4.3±2.02mg/L respectively. The average removal efficiency of BOD was 95%. The lower values of the indicative parameters were when the LTS was stabilizing and attaining the required standards even without high growth in SCWs, until heavy rainfall occurred. Therefore, it is essential to install subsurface leachate interceptor drains and those connected to the leachate treatment system. It will require a proper dumpsite cover system to reduce infiltration and thus promote runoff. It is imperative to monitor and evaluate frequently the system and improve it with an aerated biological indicator pond.