Degradation of Municipal Solid Waste Landfill Leachate Using Ferrites from Spent Batteries as Heterogeneous Solar Photo-Fenton Catalyst

The municipal solid waste landfill leachates exhibit high chemical oxygen demand (COD) due to the partially degraded organic matter content. The biological treatment followed by a dilution is a commonly employed treatment for this type of wastewater. However, this process does not remove the organic content in a satisfactory level and just the dilution is an environmental problem. In the present work, it was proposed the application of zinc–manganese ferrite, synthesized from discarded batteries, as a catalyst for the heterogeneous solar photo-Fenton system applied to leachate degradation. The solar photo-Fenton process was studied as a pre- and post-step of a combined process with physical–chemical coagulation to degrade the leachate, in which it was characterized by proper techniques and had approximately 1600 mg L −1 of initial COD. The direct oxidation of the leachate resulted to 15% of COD removal and the application of the photo-Fenton process resulted in 40% of COD removal. The photo-Fenton process combined with a physical–chemical coagulation as pre-treatment resulted in a final COD of 419 mg L −1 which corresponds to 74% of COD removal, using an energy dose of 65 J cm −2 of solar irradiation (120 min). The optimized concentration of H 2 O 2 and ferrite was 10 mmol L −1 and 0.1% (w/v), respectively. The resulting treated effluent can now be redirected to the municipal wastewater treatment plant. The catalyst was totally removed from the treated solutions using a magnetic bar, since the catalyst based on zinc–manganese ferrites is a soft ferromagnetic material. It works explored alternatives for companies from Minas Gerais State (Brazil) to make the pre-treatment of the leachate before discharge. Highlights The zinc–manganese ferrites, synthesized from discarded batteries, can be used as catalysts for the heterogeneous photo-Fenton system. The zinc–manganese ferrites have good activity, high stability, and can be reused. The use of a heterogeneous photo-Fenton process with a physical–chemical coagulation as pre-treatment to treat the leachate resulted in 74% of COD removal. The resulting treated effluent can be redirected to the municipal wastewater treatment plant in accordance with Brazilian’s regulations. This work also presents some compounds that can be founded in the leachate.