The degradation processes of refractory substances in nanofiltration concentrated leachate using micro-ozonation

Concentrated leachate (CL) is the byproduct of leachate treated by the membrane separation unit after bio-treatment processes, and contains many humic-like substances. Ozonation processes were applied and optimized for the further removal of those refractory matters in this work. Micro-bubble ozonation (MB-O₃) possessed the best performance, and 76.0% and 69.9% of COD and TOC were found to be removed under the optimum conditions with ozone dosage of 2.4g/L, initial pH of 9 and reaction time of 120min. The reaction rate k in MB-O₃ was 0.0104min^-1, three times higher than that in normal O₃. The percentages of humic acid and fulvic acid in CL decreased from 24.1% to 14.3% and 49.6% to 25.0%, while that of HyI substances increased from 26.3% to 60.7%, which was also found in the fraction of <2000Da, with the occupied percentage increased from 0 to 63.0%. The humic acid-like substances might be transformed to matters with carbonyl and carboxyl group, since a continuous blue-shift was observed from Em/Ex 475/390 to 410/325nm. MB-O₃ could be a promising method for the advanced treatment of CL.