Comparison of acoustic and hydrodynamic cavitation based hybrid AOPs for COD reduction of commercial effluent from CETP.

The present work investigates the treatment of commercial effluent obtained from Common Effluent Treatment Plants (CETP) using acoustic cavitation (AC) and hydrodynamic cavitation (HC) based hybrid AOPs. Comparison of different hybrid AOPs viz. HO, Fe/HO, Fe/HO/Air, Fe/HO/SO and Fe/HO/SO/Air in combination with both AC and HC has been performed in terms of extent of chemical oxygen demand (COD) reduction and kinetic rate constants. The best results of COD reduction as 95.2% and 97.28% were obtained for AC/Fe/HO/Air and HC/Fe/HO/Air systems respectively at Fe/HO ratio of 0.1 and pH of 2 within 60 min of treatment under conditions of ultrasonic power dissipation as 150 W, inlet pressure for HC as 4 bar (as applicable depending on process) and temperature of 30 ± 2 °C. Slightly lower efficacy was established for the combination approach involving AC or HC coupled with Fe-activated SO and HO yielding COD reduction of 82.9% and 86.93% for the AC/Fe/HO/SO/Air and HC/Fe/HO/SO/Air systems respectively at Fe/HO/SO ratio of 1:40:17.5. Cost estimation on the basis of cavitational yield performed on the AC and HC based treatment systems revealed economical nature of HC based treatment. Kinetic studies were also performed by fitting the experimental data with pseudo first order kinetic model (PFOKM), generalized kinetic model (GKM) and Behnajady-Modirshahla-Ghanbery kinetic model (BMGKM). It was demonstrated that GKM provided best fitting for all the experiments whereas BMGKM was most suitable for Fenton based reactions. It was clearly established that complex CETP effluent can be effectively treated using the combined approaches based on HC with potential for larger scale operation.