Hydrodynamic cavitation: an advanced oxidation process for the degradation of bio-refractory pollutants

In recent years, water pollution has become a major problem for the environment and human health due to the industrial effluents discharged into the water bodies. Day by day, new molecules such as pesticides, dyes, and pharmaceutical drugs are being detected in the water bodies, which are bio-refractory to microorganisms. In the last two decades, scientists have tried different advanced oxidation processes (AOPs) such as Fenton, photocatalytic, hydrodynamic, acoustic cavitation processes, etc. to mineralize such complex molecules. Among these processes, hydrodynamic cavitation (HC) has emerged as a new energy-efficient technology for the treatment of various bio-refractory pollutants present in aqueous effluent. In this review, various geometrical and operating parameters of HC process have been discussed emphasizing the effect and importance of these parameters in the designing of HC reactor. The advantages of combining HC with other oxidants and AOPs such as H2O2, ozone, Fenton process, and photocatalytic process have been discussed with some recommendation for large-scale operation. It has been observed that the geometry of the HC device and other operating parameters such as operating pressure and cavitation number are the key design parameters that ultimately decide the efficacy and potentiality of HC in degrading bio-refractory pollutants on an industrial scale.