Application of Photo-Fenton oxidative process followed by adsorption in dairy effluents treatment

Wastewater from milk processing and its derivatives is highly polluting due to its complex composition. Conventional treatments do not allow the treated effluent to be reused, so more effective processes such as advanced oxidation processes (AOPs) are required. This study evaluated the efficiency of the Photo-Fenton AOP followed by adsorption in activated carbon (AC) suspension to reduce the organic load of the effluent. The effluent was characterized for conductivity, pH, chemical oxygen demand (COD), total and soluble solids, and oils and fats. The initial COD of the effluent was 630 mg.O₂/L, and the total solids content was 3703 mg/L. The AC was characterized for mesoporosity, microporosity, zero-charge pH, and Boehm's acidic and basic groups. A central composite rotational design (CCRD) was used to determine different concentrations of H₂O₂ and FeSO₄ to prepare Fenton solutions and the reaction time for the AOP treatment, with COD reduction as the response variable. The Photo-Fenton treatment achieved a maximum COD reduction of 79 % under optimized conditions (0.829 mL/L of H₂O₂, 0.625 g/L of FeSO₄ for 60 min). After photooxidative treatment, the samples were suspended in AC and filtered. Kinetic and equilibrium studies showed that the AC could remove 1666.6 mg.O₂/g per gram of AC, confirming its effectiveness as an adsorbent after the Photo-Fenton process. With the coupled Photo-Fenton/adsorption treatment, the efficiency for organic removal reached 99 %, indicating strong and efficient reduction of organic compounds. These results suggest that the treated effluent could be suitable for reuse in various industrial applications, promoting sustainable water management practices. [Display omitted] •Sequential treatment with Photo-Fenton and adsorption removes up to 99 % of COD in dairy effluent.•Photo-Fenton (0.829 mL/L of H2O2, 0.625 g/L of FeSO4) followed by activated carbon adsorption•The combined process degrades organic compounds and adsorbs persistent residues.•Activated carbon adsorption enhances efficiency after Photo-Fenton, ensuring safe reuse.•Sequential Photo-Fenton and adsorption optimize organic matter removal.