Intensification of industrial wastewater treatment using hydrodynamic cavitation combined with advanced oxidation at operating capacity of 70 L.

The present work deals with treatment of industrial wastewater with hydrodynamic cavitation (HC) combined with advanced oxidation processes (AOPs) at a pilot plant operating at a capacity of 70 L. Initially approach of only HC was studied with understanding into the effect of parameters like inlet pressure (range of 2-8 bar) and dilution factor (two cases with dilution ratio as 1:1 and 1:3). Only HC was found to give minimal chemical oxygen demand (COD) removal within 180 min and the further focus of the study was aimed to test efficiency of different oxidants in combination with HC. Oxidants used in treatment were hydrogen peroxide (H2O2), Fenton's reagent, air and oxygen. Effect of H2O2 loading was analyzed with variation of loading in the range of 5-15 g.L-1 and maximum COD removal of 30% was achieved at 15 g.L-1 loading of H2O2. Keeping 15 g.L-1 as the constant loading of H2O2, optimization of Fenton based treatment was performed with variation of Fe2+/H2O2 molar ratio in the range of 1:10-1:30. Maximum COD removal of 42% was achieved at best molar ratio of 1:20. For the very first time, air and oxygen injection were tested in combination of HC giving 15.5% and 42% COD removal respectively. Combination study of oxygen + Fenton + HC was performed at H2O2 loading of 15 g.L-1 and Fenton molar ratio as 1:20, which resulted in 63% COD removal within 180 min of treatment. Energy efficacy analysis in terms of COD reduction per unit energy and cost calculations were also performed and for process giving maximum of 63% COD removal in 180 min, cost of treatment obtained was 398 US$/m3. It was clearly established that HC in combination of Fenton and oxygen is the best approach for treatment of complex industrial wastewater.