Studies on the efficacy of ultrasonication processes in combination with advanced oxidizing agents for alum pretreated tannery waste effluent

Abstract

This study focusses on the efficacy of hybrid Ultrasonication (US) techniques for treatment of real tannery waste effluent (TWE). US treatment alone of raw TWE at an optimized amplitude of 40 % produced 20.32 % COD reduction, whereas hybrid US treatment with Fenton, H2O2, ozone and NaOCl oxidizing agents are not effective with low (11–25%) COD reduction. However higher COD removal was obtained by an alternative approach, by removing suspended matter from TWE through coagulation prior to hybrid US treatment. Alum gave higher removal than AlCl3 with COD and TSS reduction for an optimized dosage of 15 g/L. Hybrid US treatment of coagulated tannery waste effluent (CTWE) with H2O2, Fenton, NaOCl and ozone at their optimized conditions produced COD reduction of 36.82 %, 66.96 %, 35.94 %, 36.14 % respectively than 23.68 % for US alone. These hybrid US processes for CTWE exhibited good synergistic effects with coefficients varying from 1.2 to 1.67. US + Fenton was most effective to treat CTWE with highest increase in biodegradability as BI value of 0.39 increased to 0.57, maximum reduction of 66.96 % COD, 58 % TOC and 47 % BOD, at optimized dosages of Fe2+ at 4 g/L, H2O2 at 18 g/L with a synergistic coefficient of 1.2. US + Fenton had least energy requirement of 0.0005 kW h/mg COD as well as highest energy efficiency of 600 mg L/kWh and highest cavitational yield of 6.34 × 104 mgL/kWh. However, hybrid US techniques when compared to HC/ HC hybrid processes, exhibited lower cavitational yield, energy efficiency and COD reduction which is a disadvantage for large-scale real applications.