Volume 33, Issue 5

Hydrodynamic cavitation (HC) has been explored by many researchers over the years after the first publication on hydrolysis of fatty oils using HC was published by Pandit and Joshi [Pandit AB, Joshi JB. Hydrolysis of fatty oils: effect of cavitation. Chem Eng Sci 1993; 48: 3440–3442]. Before this publication, most of the studies related to cavitation in hydraulic system were concentrated to avoid the generation of cavities/cavitating conditions. The fundamental concept was to harness the energy released by cavities in a positive way for various chemical and mechanical processes. In HC, cavitation is generated by a combination of flow constriction and pressure-velocity conditions, which are monitored in such a way that cavitating conditions will be reached in a flowing system and thus generate hot spots. It allows the entire process to operate at otherwise ambient conditions of temperature and pressure while generating the cavitating conditions locally. In this review paper, we have explained in detail various cavitating devices and the effect of geometrical and operating parameters that affect the cavitation conditions. The optimization of different cavitating devices is discussed, and some strategies have been suggested for designing these devices for different applications. Also, various applications of HC such as wastewater treatment, preparation of nanoemulsions, biodiesel synthesis, water disinfection, and nanoparticle synthesis were discussed in detail.

The uncontrolled proliferation of algae and algal blooms due to excessive nutrient loading in natural and industrial water bodies is a major issue for water quality maintenance. It reduces usability of the water, imposes hazardous effects of algal toxins released from algal blooms, and creates nuisance in the operation of several industrial water units. Among several existing water treatment methods to diminish the post-algae growth effects, ultrasonication has emerged as an environmentally safe technology that does not involve any use of algaecide. The interaction of several parameters, including climatic and environmental conditions with algae growth rate, have been reviewed in this article. The effects of different acoustic operating conditions for inhibition of algae growth have also been discussed. Concern about high energy consumption led other technologies to be integrated with ultrasonication. It has enhanced the process efficiency and reduced the energy consumption as reported in some long-term field investigations and patent proposals. Several issues that require further research for making this technology widely applicable or to install an effective system design have been highlighted in this article.

Many emerging pollutants (also known as micro-pollutants) including pesticides, pharmaceutical and personal care products (PPCPs), and endocrine disrupting chemicals (EDCs) have frequently been detected in surface, ground, and drinking water at alarming concentrations. The emission and accumulation of these anthropogenic chemicals in nature is a potential threat to human health and aquatic environment. Therefore, it is essential to devise an effective and feasible technology to remove the micro-pollutants from water. Activated carbon adsorption has been introduced and utilized as a promising treatment to reduce the concentration of the emerging pollutants in water. A summary of research on the removal of pesticides, PPCPs, and EDCs by activated carbon adsorption process is presented in this report. The effects of carbon characteristics, adsorptive properties, and environmental factors on the adsorption capacity of activated carbon are reviewed. In addition, the mechanisms of the adsorption including hydrophobicity and the nature of the functional groups of activated carbon and organic compounds are discussed. Furthermore, the applied equilibrium adsorption isotherms (Langmuir, Freundlich, BET, Sips, Dubinin-Astakhov, Dubinin-Radushkevich, and Toth) and the most common kinetic models (pseudo-first- and second-order models, film and intra-particle diffusion models, and adsorption-desorption model) are also included for further investigation. This comprehensive review report aims to identify the knowledge deficiencies regarding emerging pollutant treatment via activated carbon adsorption process and open new horizons for the future research on the adsorption of emerging pollutants on activated carbon.