Electron-beam (EB) radiation technology was applied to the Kimpo coastal landfill leachate to treat the biologically refractory substances remaining after an activated sludge process. Kimpo landfill leachates were analyzed in terms of molecular weight distribution (MWD) and aquatic humic substances (AHS) before and after the activated sludge process and EB radiation. When the raw leachate with an initial BOD of 1370 mg/l was treated by the activated sludge process, about 98% of BOD was successfully removed during the 72-h batch test. However, the biodegradability of leachate, defined as BOD/DOC, decreased from 1.3 to 0.1 due to the presence of biologically refractory organic matter. Fractionation of organic matter using an ultrafiltration apparatus revealed that large organics. above MW 30,000, were the most refractory component. However, this high organic component was sharply reduced after EB radiation. The AHS of the raw leachate and the effluent from activated sludge process (AS(eff)) were estimated to be 57.7 and 64.1% of DOG, respectively. When the AS(eff) was subjected to EB radiation at a dose of 30 kGy and pH 3, DOC concentration decreased from 324 to 215 mg/l and AHS content also fell from 68.6 to 52.9%. The efficiency of EB radiation was affected by pH condition and dose. In the case of AS,(eff), pH condition was the most important parameter affecting the efficiency of EB radiation. (C) 1999 Elsevier Science Ltd. All rights reserved.