Chelate-Assisted Fenton Process at Circumneutral pH for Efficient Landfill Leachate Treatment: Process Intensification and Optimization

The Fenton process (FP) is one of the most studied advanced oxidation processes and has emerged as a promising alternative for removing a wide range of pollutants from wastewater. However, the initial pH adjustment (approximately 3) and neutralization at the end of the process are notable drawbacks that are time-consuming, increase costs, and complicate the process, ultimately restricting its widespread application. Furthermore, excess toxic Fenton sludge (FS) production increases secondary pollution and renders the process unsustainable. This study explores how including a chelating agent improves the FP for the degradation of highly complex wastewater (landfill leachate). The findings show that the suggested alternative strategy enables the process to treat leachate from its typical acidic pH (approximately 3.0) to the circumneutral range (5.5–7.5). The reduction in toxic FS production further confirms the decrease in secondary pollution, which improves the overall process’s efficiency. Under optimal conditions [pH = 6.0, ethylenediaminetetraacetic acid (EDTA) dosage = 78 mL/L, reaction time = 68 min, Fe2+ dosage = 1,250 mg/L, H2O2 dosage = 3,000 mg/L], excellent reductions of COD up to 72%, color (>85%), and total suspended solids (TSS) (>95%) are achieved, while only 15%–20% of COD removal is achieved without EDTA. A significant quadratic model (R2 > 0.92) was obtained, and the optimization criteria were effectively verified. ANOVA revealed that the most influential factor was EDTA dosage, whereas reaction time had the least influence. The chelating agent EDTA stabilized and secured iron ions while avoiding undesired reactions, such as the precipitation of iron hydroxides. Thus, the chelate-assisted FP’s unique optimization strategy (central composite design/response surface methodology) minimized the drawbacks of FP, making the process more efficient and acceptable for a wider range of applications.