Treatment of Solvent-Contaminated Water Using Vortex-Based Cavitation: Influence of Operating Pressure Drop, Temperature, Aeration, and Reactor Scale

Abstract

Hydrodynamic cavitation is being increasingly pursued for the development of an intensified and compact wastewater-treatment process. Experimental data on the degradation of water contaminated with three commonly used solvents (acetone; ethyl acetate, EA; and isopropyl alcohol, IPA) using vortex-based cavitation devices are presented. The influence of operating flow or pressure drop across cavitation devices (150 to 300 kPa), operating temperatures (20 to 45 °C), concentrations of pollutant (1000 to 50 000 ppm), and scales of the cavitation reactor (with a scaling-up factor of 4, maintaining the geometric similarity) has been reported. A new reaction-engineering model based on the number of passes through the cavitation device was developed to interpret degradation behavior. The model provides a convenient way to estimate the per-pass degradation factor from batch experiments and allows its extension to continuous processes and to more-sophisticated models for estimating the generation of hydroxyl radicals. The model showed excellent agreement with experimental data. The per-pass degradation factor exhibited a maxima with respect to pressure drop (200–250 kPa) across cavitation devices. Aeration was found to improve degradation performance up to 1 vvm ([L/min]gas/Lliquid]). The initial concentrations of acetone (1000 to 50 000 ppm) and IPA (1000 to 22 000 ppm) were found to have a negligible effect on degradation performance. The per-pass degradation factor for EA was 1.5 and 4 times that of acetone and IPA, respectively. The effect of two scales (nominal capacities of the small- and large-scale devices used were 0.3 and 1.2 m3/h, respectively) was investigated for the first time, and it was found that the per-pass degradation factor decreased with scale. The presented model and experimental data provide new insights into the application of hydrodynamic cavitation for wastewater treatment and provide a basis for further work on the scaling-up of hydrodynamic cavitation devices. The results will be useful to researchers as well as practicing engineers interested in harnessing hydrodynamic cavitation for water treatment.