Optimized coupling of photocatalysis and cavitation for phenol degradation: use of an extended-kinetic approach

The coupling of hydrodynamic cavitation (HC) and photocatalysis (PC) predominantly exhibits a complementary nature, which is highlighted through a synergistic index. However, this calculation, based on pseudo-first order kinetics, fails to accurately represent the concentration data, often skewed by the formation of reaction intermediates. To address this, an ‘extended’ kinetic approach previously developed with two parameters, which accounts for the formation of intermediates, was adopted. The PC process was optimized for a simulated wastewater containing phenol of concentration (C ₀) of 100 ppm by applying a UV-A light source of intensity 175 ± 8 W/cm ² on an operating volume (V _L) of 200 mL. Catalyst loading, solution pH and initial concentration (C ₀) were optimized. These optimal parameters were used to operate HC-PC (V _L = 3500 mL) at a comparable illumination intensity across the 2 techniques’ reactors. It was observed that phenol conversion was observable only with halved C ₀ (= 50 ppm) for the HC-PC system, increasing catalyst loading from 0.5 to 1.0 g/L exhibited no increase in phenol conversion. The obtained results from experiments were interpreted with the help of the two-parameter model. For the PC system, the initial rate constant (k ₀) exhibits a similar trend to the final oxidation extent, however, it did not compare quantitatively. The second parameter – ‘y’ showed a high finite value, denoting the need for dosing external oxidants. The trends of the two-parameters with respect to different relevant parameters presented will help leverage this kinetic approach for AOPs, while optimizing and translating processes to larger scales of operation.