Hydrolytic pretreatment of oily wastewater by immobilized lipase

The purpose of this study was to evaluate the hydrolysis of wastewater with high oil and grease (O&G) concentration from a pet food industry using immobilized lipase (IL) as a pretreatment step for anaerobic treatment through batch and continuous-flow experiments. The intrinsic Michaelis constant (Km) and maximum reaction rate (Vmax) were estimated experimentally and the Km value of IL (22.5 g O&G/L) was six-folds higher than that of the free lipase (FL) (3.6 g O&G/L), whereas Vmax of both FL (31.3 mM/g min) and IL (33.1 mM/g min) were similar. Preliminary batch anaerobic respirometric experiments showed that chemical oxygen demand (COD) and O&G reduction were 49 and 45% without pretreatment and 65 and 64% with IL pretreatment respectively, while the maximum growth rate (μmax) for pretreated wastewater (0.17 d−1) was 3.4-folds higher than that of raw wastewater (0.05 d−1) with similar Monod half-saturation constants (Ks ∼ 2.7 g COD/L). The continuous-flow experimental study showed the feasibility of employing the hybrid packed bed reactor (PBR)-upflow anaerobic sludge blanket (UASB) system for the treatment of high-strength oily wastewater, as reflected by its ability to operate at an oil loading rate (LR) of 4.9 kg O&G/m3 d (to the PBR) without any problems for a period of 100 days. During pseudo-steady-state conditions, the hybrid UASB produced relatively higher biogas compared to the control UASB, The effluent COD and O&G concentrations of hybrid system were 100 mg/L lower than that of the control UASB reactor and no foam production was observed in the hybrid UASB compared to the control UASB reactor.