Simultaneous removal of Cr and organic matters via coupling Cr-Fenton-like reaction with Cr flocculation: The key role of Cr flocs on coupling effect

Removal of Cr and Organic Matter from Real Tannery Wastewater via Fenton-like Process Using Commercial Nano-Scale Zero-Valent Iron

“…This result indicated that organic matter removal increased as the initial pH value decreased, which can be attributed to the generation of more hydroxyl radicals via nZVI/H 2 O 2 under acidic conditions. The reduction in COD concentration indicates floc disruption, protein lysis, and the release of organic materials into the liquid phase [7]. Similar outcomes were reported by Hodaifa et al in their study of Fenton-like processes for olive oil mill wastewater treatment, which revealed that operating conditions determine high rates of COD conversion [42].…”

“…In the presence of nZVI, COD removal occurs initially through oxidation processes. Subsequently, the increased rate of removal occurs through coagulation and flocculation processes [7]. In this sense, neutralization is a critical aspect in the process of scaling to promote coagulation, flocculation, and sedimentation.…”

“…Additionally, these ions react with peroxide to form OH• and OH − , generating regions around the flocs where the pH is more alkaline than that in the rest of the medium, facilitating Cr flocculation. Inevitably, Cr (VI) is formed via the oxidation of Cr (III) in the flocs; however, due to the acidic conditions of the external medium, it can be reduced again [7]. Figure 4b shows that the COD removal efficiency was lower when chloride ions were present in the medium.…”

“…Increased COD removal can be attributed to Cr's capacity to generate reactive oxygen species (ROS) in the presence of H 2 O 2 , thereby contributing to the degradation of organic compounds. Cr can produce free radicals through Cr (III) to Cr (VI) oxidation with H 2 O 2 via the Haber-Weiss-type reaction, leading to a Cr Fenton-like reaction [7,20]. Although Cr (III) typically flocculates in solutions with a pH > 8, it can also occur when the pH < 5.…”

“…Additionally, TWT contains a high level of leather-related, co-existing substances, such as animal fat, keratin, and collagen. This organic matter often coexists with Cr-total contamination and Cl − , which complicates and increases the cost of treating wastewater [7]. Several treatment methods have been developed to remove Cr-total and organic matter from TWT.…”