A Perspective on the Catalytic Treatment of Tannery Wastewater

Abstract

Tanning is the transformation process which converts animal hides and skin into stable products called leather generated highly turbid, colored and foul smelling waste water. The tannery waste water contains highly recalcitrant chemical pollutants such as chromium-complexed collagen, surfactants, sulfides chlorides and salts. In addition, tannery waste water often contains high concentration of biological oxygen demand (BOD), chemical oxygen demand (COD) suspended solids (SS), nitrogen, many researchers reported that several conventional methods namely, coagulation-flocculation  precipitation, oxidation, ion exchange and membrane filtration, ozonation have been utilized to treat tannery wastewater. These methods have associated shortcomings such as high cost of reagents, generation of toxic sludge, low efficiency, not only that organic pollutants were only transfer from one phase to another and may even become more toxic than the compounds. In the recent times, heterogeneous photocatalysis involving the use of metal oxide such as CdS, CuO, ZnO, SiO₂ and Fe₂O₃ have received considerable attention among researchers due to capability to degrade numerous organic contaminants into carbon dioxide and water. Among the aforementioned metal oxide nanocatalysts, ZnO  nanoparticles have emerged as the candidate in photocalysis due to its low cost availability, excellent chemical stability, non toxicity and high initial rate of activities.  Similarly, ZnO nanoparticles are relatively cheap and have the ability to absorb a wide range of UV spectrum compared to other metal oxides. The review highlighted all these details and simultaneously provided insights into directions for further investigations.