Formation of Trihalomethanes (THMs) during Chlorination of Landfill Leachate

Co-treatment of landfill leachate and sewage in a traditional wastewater treatment plant (WWTP) is a very common leachate management method in the United States. However, biologically recalcitrant and humic-like leachate organic matters (the major fraction of mature leachate organics) cannot be truly removed by the aerobic biodegradation in WWTPs. Prior to effluent discharge from WWTPs, chlorine for disinfection may largely transform the humic-like substances to various disinfection by-products (DBPs). In this study, formation potential (FP) of trihalomethanes (THMs) (the most common DBP type) during leachate chlorination was evaluated. Seven-day DBP FP tests were conducted to measure THM formation potential (THMFP) of a typical mature leachate and a representative secondary effluent. Results show that the THMFP of the tested leachate was 20,227 ppb, much greater than that (180 ppb) of a WWTP secondary effluent. Different molecular weight (MW) leachate organics fractions exhibited different FP patterns. Most of THMs (65%) was formed from the lowest MW organics groups (<1,000 Da); however, the THMFP/DOC for the < 1,000 Da group was the lowest (62 ppb/ppm), in comparisons with 222, 258, and 261 ppb/ppm of 1,000-10,000, 10,000-100,000, and > 100,000 Da leachate organics. The results demonstrated that WWTP co-treatment of leachate should be carefully selected in the areas that depend heavily upon water reuse or where treated wastewater accounts for a high fraction of downstream drinking water plant’s raw water.