Treatment of membrane concentrated landfill leachate by a heterogeneous electro-Fenton process with an iron-loaded needle coke cathode

Mature membrane concentrated landfill leachate is one of the most recalcitrant wastewaters due to its high pollutant concentration, poor biodegradability, and stable organic structure. In this study, a heterogeneous electro-Fenton system was constructed using a Fe-loaded needle coke composite electrode as a cathode to treat the membrane concentrated landfill leachate from a local closed landfill. The reaction conditions were evaluated and optimized by the response surface method based on Box-Behnken design. A second-order polynomial model with COD removal rate as the response and initial pH, plate spacing, and applied voltage as independent variables were established. After treatment by the heterogeneous electro-Fenton process with the needle coke composite cathode under the optimal conditions of applied voltage 10 V, initial pH 3.6, and the plate spacing 1.4 cm, the COD and color removal rates of the membrane concentrate were up to 71.9% and 99.8%, respectively, and the biodegradability was significantly improved with the BOD5/COD increasing from 0.003 to 0.379. Various spectral analyses of the wastewater before and after electro-Fenton treatment with the needle coke composite cathode demonstrated that most of the macromolecular organic pollutants in the landfill leachate concentrate including aromatic compounds, simple aromatic protein compounds, soluble microbial by-products, and humic acid were significantly degraded. As a result, the electro-Fenton technique with the needle coke composite cathodes is one of the cost-effective options for treating membrane concentrated landfill leachate.