Kinetics of wet air oxidation pretreatment and biodegradability enhancement of a complex industrial wastewater

A kinetic study of wet air oxidation pretreatment and induced biodegradability enhancement of a model complex wastewater was studied in the temperature range of 150–200 °C, air pressure 6–12 bar (0.6–1.2 MPa), reaction time 15–120 min and agitation 150–500 rpm. Based on free radical mechanism, a kinetic model is postulated where the electron transfer from air (oxygen) to the substrate was assumed to initiate the free radical generation. According to the model, reaction orders for wet oxidation pretreatment (in terms of COD degradation rate) were found to be 1.0, 0.42 and 0.22 for COD and oxygen partial pressure respectively. The WAO pretreatment led to reorientation and/or breakdown of complex biologically recalcitrant molecules with 3–5-fold increase in biodegradability index. The kinetics of biodegradability index enhancement was successfully correlated with COD degradation kinetics.