Combined oxidation processes based on ultrasound, hydrodynamic cavitation and chemical oxidants for treatment of real industrial wastewater from cellulosic fiber manufacturing sector

Abstract

The present work reports the application of cavitation for the real industrial effluent treatment, which was derived from the cellulosic fiber manufacturing sector, individually or in combination with advanced oxidation processes. Cavitation has been applied with the objective of reducing the chemical oxygen demand (COD) of the industrial effluent and to study its simultaneous effect on the total dissolved solids (TDS). A combination of cavitation with different additives/oxidants viz. hydrogen peroxide (H2O2), ozone (O3), sodium hypochlorite (NaCLO), and Fenton's reagent have been studied. Ultrasonic horn operating at an acoustic power of 120 W with a frequency of 20 kHz and duty cycle of 80% (8 sec ON, 2 sec OFF) was used for treatment based on ultrasound. Under optimized conditions, it was established that a combination of ultrasound (US) with Fenton’s reagent using an optimum mole ratio of H2O2/Fe2+ of 3 followed by lime coagulation gave a maximum COD reduction of 92% and also resulted in TDS reduction of 31%. Studies were also performed using a hydrodynamic cavitation (HC) reactor (10 L capacity) where slit venturi was used as a cavitating device. It has been observed that a combination of HC with Fenton's reagent at molar ratio of H2O2/Fe2+ as 3 gave the maximum COD reduction of 86% and a TDS reduction of 47%. It was also established that lime treatment played an important role in separating the sludge formed during the Fenton oxidation treatment and in converting brownish colored effluent to colorless effluent. Overall, it has been established that cavitation coupled with the Fenton oxidation was most the efficient among all studied combinations giving a good COD reduction as well as TDS reduction with a final colourless nature of effluent.