Catalytic ozonation of real food wastewater using catalyst synthesized from waste

Abstract

ABSTRACT In the present study, complex wastewater from the food industry was used to study the effect of ozonation and catalysed ozonation for chemical oxygen demand (COD) removal. The catalysts used were synthesized from agro-waste, activated carbon (AC) and plastic waste, multiwalled carbon nanotubes (MWCNTs)(MWCNT). The effect of various operating parameters, like ozone dosage, catalyst dosage, pH, on COD removal of food industry wastewater was investigated. The maximum COD removal was observed at ozone dose of 2gm/hr. MWCNTs(MWCNT) catalysed ozonation removes 85% COD and 48% total organic carbon (TOC) removal within 180 min at pH 9 and 74% COD and 36% TOC removal was observed for activated carbon catalysed ozonation for the same experimental conditions. A significant inhibition of COD removal was observed in the presence of tertiary-butyl alcohol. Using para-chlorobenzoic acid (p-CBA) as a probe compound, the hydroxyl radical exposure was determined for AC and MWCNT catalysed ozonation. The hydroxyl radical exposure was measured to understand the mechanism of catalytic ozonation and compare the performance of two different catalysts in terms of hydroxyl radical generation. It was found that hydroxyl radical exposure increases with increasing catalyst dose, which confirms the hydroxyl radical (OH.) pathway for COD reduction. The kinetic studies showed a 5.5time increment in rate for MWCNT catalysed ozonation and a 4 time increment for activated carbon catalysed ozonation when compared with standalone ozonation. The synergistic factor for MWCNTs and ozone was found to be 1.83 and for activated carbon and ozone, 1.5. Highlights Catalysts used were synthesized from waste. Application of activated carbon and multiwalled carbon nanotubes for catalytic ozonation of real food wastewater was investigated. Effectiveness of standalone ozonation and catalytic ozonation was identified and compared. A multiwalled carbon nanotube presents higher catalytic performance than activated carbon for ozonation of real food wastewater. Hydroxyl radical mechanism of catalytic ozonation was confirmed by using p-CBA as a probe compound.