Application of advanced oxidation processes and cavitation techniques for treatment of tannery wastewater—A review

Advanced Oxidation Processes and Biotechnological Alternatives for the Treatment of Tannery Wastewater

“…In AOPs, the reaction of OH and the various pollutants present in tannery effluents results in mineral end products that produce inorganic ions and carbon dioxide [ 114 , 115 ]. The efficiency of each process depends on the physicochemical characteristics of the pollutants present in tannery effluents, as well as on the generation of hydroxyl radicals.…”

“…Ozone is a technology that has been reported in the treatment of dyeing water, reaching removals of 90–98% COD and 96% color [ 104 , 105 ]; the efficiency of the process depends largely on pH; at acidic values < 4.5, the reaction is direct, molecular ozone dominates the reaction being selective mainly in the destruction of chromophore groups, while at the pH > 7, ozone decomposes, generating OH which is less selective and has a higher oxidation potential; the ozone flow rate is another important variable, the percentage of removal is directly proportional to the ozone flow rate with respect to time; increasing the ozone rate increases the removal efficiency. It has been reported that excess ozone can lead to the formation of residual H 2 O 2 , allowing the wastewater concentration to be increased so that the COD present can be degraded by the excess H 2 O 2 [ 114 ].…”

“…In relation to photocatalytic processes, photo-Fenton is one of the most studied in tannery effluents, and has achieved removals of 70–90 % COD, 86–98% color [ 100 , 111 ] and 90% Cr [ 114 ]; the efficiency of the process depends largely on the pH of the solution, the optimal range of higher catalytic activity is 2.8–3.0, pH values > 5 generate ferric hydroxides that reduce the reactivity of OH, while at values below 2, complex iron species are formed that react more slowly with H 2 O 2 , decreasing the efficiency of the process [ 116 ]; the amount of ferrous ions generated also affects the process; excess concentrations in the solution can generate precipitates, increasing the TDS concentration [ 117 ]. Finally, the irradiation time is another variable that affects the process; this should be as low as possible to minimize energy consumption without affecting process efficiency.…”

“…Depending on the cavitation mode, four different forms are distinguished: acoustic cavitation, hydrodynamic cavitation, cavitation, optical cavitation and particle cavitation. It has been reported that acoustic cavitation and hydrodynamic cavitation have proven to be effective techniques for the treatment of tannery effluents [ 114 , 120 ]. The process parameters that affect acoustic cavitation are as follows: ultrasonic power; since the amount of OH generation and the energy dissipated depend on the ultrasonic power and the immersion depth of the probe, it is essential that the immersion depth of the probe is adequate for the propagation and dissipation of the wave.…”

Performance Evaluation of Ultra-Violet Light and Iron Oxide Nanoparticles for the Treatment of Synthetic Petroleum Wastewater: Kinetics of COD Removal

“…The AOPs have been reported to have widespread application of treating organic and inorganic pollutants present in water and wastewater [ 10 , 11 , 12 ]. These processes oxidize the complex organic pollutants found to be difficult to degrade biologically into simpler end products or degrades them to CO 2 and H 2 O. AOP has been effectively utilized as a pre-treatment technique to remove toxic pollutants that interfere with or escape past wastewater treatment processes [ 13 ].…”