Removing refractory organic matter from nanofiltration concentrated landfill leachate by electrooxidation combined with electrocoagulation: Characteristics and implication for leachate management

To guide optimization of electrochemical process for landfill leachate concentrate (LLC), systematical experiments were performed on treating LLC with electrooxidation (EO), electrocoagulation (EC) and various combined processes. The results show that EC for 60 min followed by EO for 180 min gave the most satisfactory treatment performance, in which the removal rates of TOC, UV254, COD and CN were 79.00%, 97.30%, 80.32% and 95.0%, respectively. Three fluorescent components were identified in LLC, fulvic acid-like substances (C1), humic-like (C2) substances and long-wave humus (C3) by fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PALAFAC). EC effectively remove most of humic-like humus from LLC, and EO could remove fulvic acid (FA) and humic acid (HA) simultaneously and promote the transformation of FA to hydrophilic (HyI). Compared with EC after EO (EO + EC), EO after EC (EC + EO) was more effective in reducing aromaticity and molecular weight, and could remove humus more efficiently. The characteristics of degrading organic matter from LLC were further verified with XAD-8 resin separation technology, which is beneficial to reduce the treatment load of sequent EO. Improving the performance of EC to remove large molecule humic organic matters is vital to comprehensively manage landfill leachate with lower cost.