Modeling ozonation pretreatment parameters of distillery wastewater for improved biodegradability

In this study, ozonation pretreatment of real distillery wastewater (DWW) for biodegradability enhancement was undertaken. Response surface methodology was used to model the value of effective parameters, including ozonation duration and initial chemical oxygen demand (COD) concentration, and to estimate linear interactions and quadratic effects. The analysis of variance confirmed the adequate description of all the responses by the quadratic model employed. During ozonation, the pH of the DWW increased in acidity from 4.53 to 4.05, indicating the formation of acidic intermediates. A 60% reduction in color was observed signifying the oxidation of the color causing biorecalcitrant aromatic compounds and confirmed by the reduction in ultraviolet absorbance at λ_max of 254 nm. Moreover, an increase in change in oxidation state from -0.1 to 0.4 was attributed to the declined aromaticity and the formation of aliphatic structures. From the measurement of the ratio of biochemical: chemical oxygen demand (BOD₅:COD), an increase from 0.48 to 0.72 confirmed improved biodegradability. Optimization studies aimed at achieving maximum improved biodegradability at maximum ozone transfer efficiency yielded optimum ozonation pretreatment parameters of initial COD of 4.1 g L^-1 and duration of 64 min.