Characterization of dissolved organic matter during the O-based advanced oxidation of mature landfill leachate with and without biological pre-treatment and operating cost analysis.

In this study, the organic matter in an O-based advanced oxidation process (AOP) for treating raw leachate (RL) and bio-treated leachate (BTL) was characterized. The optimal conditions for COD removal in RL and BTL treatment were as follows: initial pH of 6.0 and HO dosage of 9 mL 30% HO L leachate, and initial pH of 12 without HO addition, respectively. HO addition had little influence on COD removal in the BTL treatment as sufficient hydroxyl radicals may not be produced at extremely high pH levels. The differences in the alkalinity between RL and BTL caused differences in the optimum pH of the AOPs. Overall, the initial pH more affected COD removal than the HO dosage. O-based AOP converted organics with high molecular weight fractions into low ones. Meanwhile, it preferentially degraded hydrophobic substances over hydrophilic substances. The organic matter in the BTL contained more refractory and hydrophobic fractions; therefore, higher COD removal was achieved in the treatment of RL. The organics in the treatment of RL and BTL were identified by excitation-emission matrix spectroscopy combined with parallel factor analysis, and their degradation decreased in the following order: terrestrial humic-like > microbial humic-like > combination of tryptophan and humic-like components. O-based AOP significantly enhanced biodegradability. According to the economic analysis results, as an intermediate treatment, O-based AOP is a cost-effective strategy of ensuring that leachate effluent meets the discharge standards, with the lowest operating cost of $4.62 m. This study provides a reference for the application of O-based AOP in full-scale landfill leachate treatment.