Ozonolysis Post-Treatment of Anaerobically Digested Distillery Wastewater Effluent

ABSTRACT

In this study, the ozonolysis of real anaerobically digested distillery wastewater (DWW) was carried out. The effect of operating parameters, such as pH, initial concentration, and ozone dosage, on the efficiency of ozone utilization, color removal, and sludge solubilization was studied. The highest ozone utilization of 99% was observed at the highest initial concentration (COD of 3000 mg/L) and lowest ozone flowrate (22.5 mg O₃/L/min), but with a very low color reduction of 20%, after 60 minutes of ozonolysis. To achieve a higher color reduction >80% and at ozone utilization >95%, the DWW had to be diluted twice (COD 1500 mg/L), and the flowrate doubled to 45 mg O₃/L/min. The reduction in color signified the oxidation of the color causing biorecalcitrant aromatic melanoidin compounds. This was confirmed by the 47% reduction in ultraviolet absorbance at 254 nm indicating the breakdown of the complex aromatic compounds into low molecular weight organics. Moreover, increases in average oxidation state from −0.6 to −0.2 suggested a decline in aromaticity and formation of easily biodegradable aliphatic compounds. The ozonolysis process was found to follow the first-order reaction kinetic model with the highest rate constant of 0.0326 min⁻¹ obtained. A reduction in suspended COD by 88% indicated solubilization of the sludge contained in the effluent.

KEYWORDS:

• Ozone
• aromaticity
• color removal
• distillery wastewater
• energy demand
• ozone utilization
• sludge solubilization

Additional information

Funding

This work was financially supported by the Water Research Commission [WRC, Project no. K5/2773/3], Sasol, and National Research Foundation (postdoctoral scholarship), all from South Africa.