A TREATMENT SYSTEM FOR LANDFILL LEACHATE

Landfill leachate is a potential source of ground and surface water contamination and causes extensive pollution if it is not properly collected, treated and disposed of. The objective of the research was to study a combined advanced oxidation process (AOP) with sequencing batch reactor (SBR) system for treatment of mature landfill leachate so as to meet the discharge standard, particularly in terms of COD, BOD5 and suspended solids. Fenton and photo-Fenton processes were applied to the preliminary treated (adjusted to pH 3 and 1-h settling) leachate and response surface methodology (RSM) was used to optimize the processes for removal of COD, colour and ammonia nitrogen (NH3-N). The optimum operating conditions for Fenton treatment were at about H2O2/COD molar ratio 2.25, H2O2/Fe2+ molar ratio 10.0 and 1.5 h reaction time for 51% COD removal, 77% colour removal and 84% NH3-N removal, whereas the optimum operating conditions for photo-Fenton treatment were H2O2/COD molar ratio 3.75, H2O2/Fe2+ molar ratio 10.0 and 1.5 h irradiation time for 68% COD removal, 81% colour removal and 80% NH3-N removal. The biodegradability (BOD5/COD ratio) of the Fenton and photo-Fenton treated leachate were 0.21 and 0.33, respectively under optimum operating conditions. Photo-Fenton treatment under Fenton process optimum operating conditions, i.e. H2O2/COD molar ratio 2.25, H2O2/Fe2+ molar ratio 10.0 (lower dosages of the Fenton reagent) and 1.5 h irradiation time, was conducted and 65% COD removal, 83% colour removal and 80% NH3-N removal were achieved, and the biodegradability was 0.35. Aerobic sequencing batch reactor (SBR) treatment of the photo-Fenton treated leachate resulted in soluble COD, BOD5 and NH3-N removal of 78, 81 and 94%, respectively. The final effluent characteristics were COD 92 mg/L, soluble COD 71 mg/L, BOD5 26 mg/L, NH3-N 7 mg/L, total phosphorus 6.4 mg/L, suspended solids 38 mg/L and colour 46 Pt-Co Units, and met the Malaysian discharge standard (B) (COD 100 mg/L, BOD5 50 mg/L and suspended solids 100 mg/L). The study shows that combined photo-Fenton-SBR provides effective treatment of a mature landfill leachate.