Advanced treatment of tannery effluent from Fez City (Morocco) using a sequence of aerobic and sono-photo-Fenton processes

This work aims to purify real tannery wastewater (TWW) after a physicochemical characterization. A pretreatment using air stripping (aerobic pretreatment; AP) was first applied and compared to anaerobic pretreatment (ANP). The COD and BOD₅ were highly removed by AP, reaching 86% and 88% compared to ANP, which only achieved 48% and 55%, respectively. Following the AP, the sono-photo-Fenton (SPF) process was applied as post-treatment. The optimal conditions pH = 3, [H₂O₂] = 1834 mg/L, and [Fe²⁺] = 1281 mg/L improved the COD, color and BOD₅ removal of 96%, 98%, and 98%, respectively. Turbidity, N-NO₃^-, and N-NO₂^- were completely removed (100%) by the combined processes (AP+SPF), while Cr, Cl^-, and N-NH₄⁺ were reduced to 99%, 97%, and 99%, respectively. Finally, phytotoxicity tests were performed to confirm the efficiency of the sequential processes. The highest germination percentage, germination rate index, and seedling vigor index for the grains <i>wheat</i> and <i>Medicago sativa</i> were observed using the TWW treated by the AP+SPF, followed by those treated by AP alone. In contrast, no germination indicators were noticed in raw TWW. These findings highlight the significant purification effectiveness of the sequential processes of AP and SPF post-treatment, which suggests the potential use of this combination for the efficient treatment of real liquid effluents.