Sonochemical Reactors.

Sonochemical reactors are based on the generation of cavitational events using ultrasound and offer immense potential for the intensification of physical and chemical processing applications. The present work presents a critical analysis of the underlying mechanisms for intensification, available reactor configurations and overview of the different applications exploited successfully, though mostly at laboratory scales. Guidelines have also been presented for optimum selection of the important operating parameters (frequency and intensity of irradiation, temperature and liquid physicochemical properties) as well as the geometric parameters (type of reactor configuration and the number/position of the transducers) so as to maximize the process intensification benefits. The key areas for future work so as to transform the successful technique at laboratory/pilot scale into commercial technology have also been discussed. Overall, it has been established that there is immense potential for sonochemical reactors for process intensification leading to greener processing and economic benefits. Combined efforts from a wide range of disciplines such as material science, physics, chemistry and chemical engineers are required to harness the benefits at commercial scale operation.

Intensification of biogas production using pretreatment based on hydrodynamic cavitation.

The present work investigates the application of hydrodynamic cavitation (HC) for the pretreatment of wheat straw with an objective of enhancing the biogas production. The hydrodynamic cavitation reactor is based on a stator and rotor assembly. The effect of three different speeds of rotor (2300, 2500, 2700 rpm), wheat straw to water ratios (0.5%, 1% and 1.5% wt/wt) and also treatment times as 2, 4 and 6 min have been investigated in the work using the design of experiments (DOE) approach. It was observed that the methane yield of 31.8 ml was obtained with untreated wheat straw whereas 77.9 ml was obtained with HC pre-treated wheat straw confirming the favourable changes during the pre-treatment. The combined pre-treatment using KOH and HC gave maximum yield of biogas as 172.3 ml. Overall, it has been established that significant enhancement in the biogas production can be obtained due to the pretreatment using HC which can also be further intensified by combination with chemical treatment.

Combined treatment technology based on synergism between hydrodynamic cavitation and advanced oxidation processes.

The present work highlights the novel approach of combination of hydrodynamic cavitation and advanced oxidation processes for wastewater treatment. The initial part of the work concentrates on the critical analysis of the literature related to the combined approaches based on hydrodynamic cavitation followed by a case study of triazophos degradation using different approaches. The analysis of different combinations based on hydrodynamic cavitation with the Fenton chemistry, advanced Fenton chemistry, ozonation, photocatalytic oxidation, and use of hydrogen peroxide has been highlighted with recommendations for important design parameters. Subsequently degradation of triazophos pesticide in aqueous solution (20 ppm solution of commercially available triazophos pesticide) has been investigated using hydrodynamic cavitation and ozonation operated individually and in combination for the first time. Effect of different operating parameters like inlet pressure (1-8 bar) and initial pH (2.5-8) have been investigated initially. The effect of addition of Fenton's reagent at different loadings on the extent of degradation has also been investigated. The combined method of hydrodynamic cavitation and ozone has been studied using two approaches of injecting ozone in the solution tank and at the orifice (at the flow rate of 0.576 g/h and 1.95 g/h). About 50% degradation of triazophos was achieved by hydrodynamic cavitation alone under optimized operating parameters. About 80% degradation of triazophos was achieved by combination of hydrodynamic cavitation and Fenton's reagent whereas complete degradation was achieved using combination of hydrodynamic cavitation and ozonation. TOC removal of 96% was also obtained for the combination of ozone and hydrodynamic cavitation making it the best treatment strategy for removal of triazophos.

Degradation of imidacloprid containing wastewaters using ultrasound based treatment strategies.

The present work deals with application of sonochemical reactors for the treatment of imidacloprid containing wastewaters either individually or in combination with other advanced oxidation processes. Experiments have been performed using two different configurations of sonochemical reactors viz. ultrasonic horn (20 kHz frequency and rated power of 240 W) and ultrasonic bath equipped with radially vibrating horn (25 kHz frequency and 1 kW rated power). The work also investigates the effect of addition of process intensifying agents such as H2O2 and CuO, which can enhance the production of free radicals in the system. The combination studies with advanced oxidation process involve the advanced Fenton process and combination of ultrasound with UV based oxidation. The extent of degradation obtained using combination of US and H2O2 at optimum loading of H2O2 was found to be 92.7% whereas 96.5% degradation of imidacloprid was achieved using the combination of US and advanced Fenton process. The process involving the combination of US, UV and H2O2 was found to be the best treatment approach where complete degradation of imidacloprid was obtained with 79% TOC removal. It has been established that the use of cavitation in combination with different oxidation processes can be effectively used for the treatment of imidacloprid containing wastewater.

Degradation of imidacloprid using combined advanced oxidation processes based on hydrodynamic cavitation.

The harmful effects of wastewaters containing pesticides or insecticides on human and aquatic life impart the need of effectively treating the wastewater streams containing these contaminants. In the present work, hydrodynamic cavitation reactors have been applied for the degradation of imidacloprid with process intensification studies based on different additives and combination with other similar processes. Effect of different operating parameters viz. concentration (20-60 ppm), pressure (1-8 bar), temperature (34 °C, 39 °C and 42 °C) and initial pH (2.5-8.3) has been investigated initially using orifice plate as cavitating device. It has been observed that 23.85% degradation of imidacloprid is obtained at optimized set of operating parameters. The efficacy of different process intensifying approaches based on the use of hydrogen peroxide (20-80 ppm), Fenton's reagent (H2O2:FeSO4 ratio as 1:1, 1:2, 2:1, 2:2, 4:1 and 4:2), advanced Fenton process (H2O2:Iron Powder ratio as 1:1, 2:1 and 4:1) and combination of Na2S2O8 and FeSO4 (FeSO4:Na2S2O8 ratio as 1:1, 1:2, 1:3 and 1:4) on the extent of degradation has been investigated. It was observed that near complete degradation of imidacloprid was achieved in all the cases at optimized values of process intensifying parameters. The time required for complete degradation of imidacloprid for approach based on hydrogen peroxide was 120 min where as for the Fenton and advance Fenton process, the required time was only 60 min. To check the effectiveness of hydrodynamic cavitation with different cavitating devices, few experiments were also performed with the help of slit venturi as a cavitating device at already optimized values of parameters. The present work has conclusively established that combined processes based on hydrodynamic cavitation can be effectively used for complete degradation of imidacloprid.