Sequential treatment of young landfill leachate by aeration and UV/US/activated persulfate-hydrogen peroxide: performance, optimization and phytotoxicity evaluation

A comprehensive treatment approach for young leachate landfill (YLL) from Fez City was investigated using an integral system involving aeration as a pretreatment before the binary oxidation process using hydrogen peroxide (HP)/persulfate (PS) as oxidants, in which UV-A irradiation and ultrasonic (US) are used as activators (HP-PS-US-UV-A). The initial treatment by aeration resulted in COD, color, and Abs₂₅₄ removal efficiencies of 54%, 61%, and 55%, respectively. The efficiency of the AOP was statistically evaluated, and the optimal operating conditions were determined by Box-Behnken design (BBD) to investigate the effects of three operating variables (pH, [S₂O₈²⁻], and [H₂O₂]) on three target responses: COD, Abs₂₅₄, and color removal. The statistical and graphical analyses indicated that the sequential process with aeration as pretreatment and subsequent application of the HP-PS-US-UV-A system achieves cumulative maximum removal of 89% of COD, 99% of color, and 96% of Abs₂₅₄, under the optimal operating conditions of the H₂O₂/S₂O₈²⁻/UV-A/US process as [H₂O₂] = 500 mg/L, [S₂O₈²⁻] = 1671 mg/L, and pH = 3. Microbiological analyses showed complete removal of total coliforms, fecal coliforms, and total mesophilic flora using sequential application of AOPs and aeration treatment. Using the bioindicators of Medicago sativa (Alfalfa), namely seed germination and root elongation, the phytotoxicity of both treated and untreated leachate samples was assessed. Results showed a noteworthy phytotoxicity decrease by applying the combined processes. The outcomes were remarkable, not only were exceptionally high pollutant removal rates achieved, but it was also discovered that the treated landfill leachate could meet environmental standards for reuse in industrial processes or even in agriculture. This innovation not only provides a solution for the efficient treatment of young landfill leachate but also opens the door to new applications for landfill leachate reuse on a broad scale, contributing to global sustainability efforts.