Improved processes involving hydrodynamic cavitation and oxidants for treatment of real industrial effluent

The present study focuses on the use of hydrodynamic cavitation (HC) alone and in combination with oxidants as pre-treatment for conventional biological treatment with an objective of enhancing the treatability of industrial effluent. Under fixed conditions of inlet pressure (4 bar) and pH (4), chemical oxygen demand (COD) reduction has been investigated using HC alone and its combination with hydrogen peroxide (H2O2), O-3 and Fenton's reagent. The individual operation of HC resulted in only 21.6% of reduction in 120 min of treatment with rate constant of 2.1 x 10(-3) min(-1). The combination of HC + H2O2, HC + O-3 and HC + Fenton yielded significantly enhanced COD reduction than the treatment using HC alone with actual values as 39.5%, 52.8%, and 72.1% respectively. Improvements in primary and tertiary treatment options have also been investigated in the current work. The coagulation using alum as primary treatment to HC + Fenton process gave overall enhanced COD reduction of about 80%. Subsequent conventional biological oxidation resulted in COD reduction of about 98%. Finally, the effluent obtained from biological treatment was filtered to remove biomass and disinfected using sodium hypochlorite. After all the steps of treatment, the final COD obtained was <= 250 mgO(2)/dm(3) which is suitable for discharge. The different treatment approaches were compared based on the power consumption and the operational cost. Overall, an improved treatment scheme involving HC + Fenton, conventional biological treatment and chemical oxidants was demonstrated for treatment showing compliance for the treated effluent.