Coupled AOPs as a mitigation strategy for synergetic environmental remediation in small scale environments: the case of sono-galvano-Fenton technique against recalcitrant pollutant in water

The Sono-Galvano-Fenton is a hybrid advanced oxidation process designed to harness the advantages of each process, namely the in-situ production of the Fe²⁺ catalyst (through the Galvano-Fenton process) and hydrogen peroxide (H2O2; through sonochemistry), as well as the plausible synergetic production of the hydroxyl radical (HO^●). In the present study, the hybrid technique is applied to the degradation of Malachite Green using different coupling strategies, at an acoustic frequency of 600 kHz and an acoustic power of 120 W, with a pre-optimized electrochemical configuration of 1 anode to 6 cathodes. A numerical model is also applied to assess the role of sonication at both microscopic and macroscopic scales. The experimental results revealed an extended residence time of the emerging pollutant within the 300 mL reactor in batch mode when both techniques are coupled in series, offering an advanced purely sonochemical degradation of the extent of Fenton reagent H₂O_{2 production}. The process is then engineered in continuous mode with recirculation of the treated solution to overcome this limit. The numerical model of sonolysis in an air atmosphere at the reactor scale demonstrated apicomolar production of hydrogen peroxide and hydroxyl radicals at 200 kHz, suggesting a frequency shift toward this value to enhance both processes ' coupling.