Treatment of landfill leachate with combined biological and chemical processes: changes in the dissolved organic matter and functional groups

Leachates contain complicated and hazardous substances that need multiple treatment processes to meet the discharge standards. Few studies have considered the changes in different fractions, based on their molecular weight (MW), of dissolved organic matter, during the different treatment processes. In this study, we investigated the application of a biological method, using sequencing batch reactors, and a chemical method, using the electro-Fenton oxidation process, in combination. The combined treatment, and the electro-Fenton process alone, was applied to a landfill leachate. Samples taken at various points during the treatment processes were fractionated according to their MW using ultra-membranes; this divided the samples into their less biodegradable constituents (0.45 μm: >10 kDa MW), their bio-refractory constituents (10-1 kDa MW) and their biodegradable constituents (<1 kDa MW). The dominant contributors to the chemical oxygen demand (COD) in the raw leachate comprised the biodegradable constituents (79% of total COD). The COD was reduced to 33.6% and 18.5% of its original levels, by the electro-Fenton process alone and the combined treatment, respectively. Based on the absorption intensities in the Fourier transform infrared (FTIR) spectra, the functional groups in the raw leachate were reduced by the biological treatment, but changed by the electro-Fenton process.