Anaerobic treatment of Hong Kong leachate followed by chemical oxidation

Abstract

Landfill leachate of Hong Kong was first treated by the upflow anaerobic sludge blanket (UASB) process. At 37°C, pH 7.1–8.5 and a HRT of 5.1–6.6 days, the process removed 66–90% of COD in the leachate for loading rates of 1–2.4g-COD/lday depending on the strength of landfill leachate. The final effluent contained 1440–1910mg-COD/l and 70–91mg-BOD/l. About 92.5% of the total COD removed was converted to methane and the rest was converted to biomass with an average net growth yield of 0.053g-VSS/g-COD-removed. The granules developed in the UASB reactor were 0.5–1.5mm in size and exhibited good settleability. The UASB effluent was then further polished by two oxidation processes. The UASB-ozonation process removed 93.0% of the 12900mg/l of COD from the raw leachate. The UASB-Fenton-ozonation process improved the COD removal efficiency to 99.3%. The final effluent had only 85mg/l of COD and 10mg/l of BOD5. Ozonation was most effectively conducted at pH 7–8 with the addition of 300mg/l of H2O2 and for the duration of 30min. Ozonation also significantly improved the biodegradability of the organic residues. Nearly 50% of these residues could be used as carbon source in denitrification.