Recent trends in advanced oxidation process for treatment of recalcitrant industrial effluents

Abstract Rapid industrialization and a fast-growing population are continuously demanding newer materials for lavishing lifestyles. As a result, their production discharges recalcitrant pollutants as byproducts into the ecosystem. The sugar, distillery, pharmaceutical, and dairy industries are some prime and important industries that are discharging the recalcitrant effluents. These effluents are discharged in water as waste and disturb the dissolved oxygen level of the aqueous system. Such wastewater contains multiple persistent toxic components (organic and inorganic) due to which the water quality is degraded. It requires specific treatments to check the quality of the wastewater before it can be discharged into the environment. The main purpose of wastewater treatment is to remove organic compounds, solids, colors, etc., from the effluent or to convert it into a relatively less toxic form. The present conventional treatment technologies, including adsorption, filtration, biological treatment, coagulation, etc., are inefficient in completely removing such recalcitrant pollutants/solids. Advanced oxidation processes (AOPs) are effective technologies used in wastewater treatment. In a conventional oxidation process, the organics in wastewater are reduced in the presence of oxygen by the mechanism of oxidation. In AOPs, organics are reduced by the mechanism of oxidation in the presence of external energy sources such as solar energy, electric energy, ultraviolet radiation (UV), electrochemical, etc. The major advantages of AOPs are: (1) Organic compounds are reduced without transfer to another phase; (2) They are effective to all organic pollutants and some toxic metals; (3) They can be used for water disinfection; (4) They are cheaper in installation; and (5) They are efficient for small-scale installation. In AOP treatment processes, sulfate radicals (SO4•−) or hydroxyl radicals (OH•), which are generated and have a short life span, are used to reduce organic matters/certain inorganic pollutants and thereby enhance the biodegradability index of the treated wastewater. There are many methods used as AOPs, such as an ozone-based oxidation process, a Fenton oxidation process, UV photolysis, H2O2/UV, ozone/UV, photocatalysis (photo-Fenton and TiO2 photocatalysis, etc.). In this chapter, we summarize the recent advancements in AOP technology in treatment of wastewater from distilleries, dairy, sugar, paper, etc.