Kinetics of anaerobic biodegradation of synthetic dairy wastewater pretreated with lactase

Abstract

The aim of this study was to evaluate the anaerobic degradation of dairy wastewater with and without the application of lactase. Two UASB reactors (16 L) were built to treat synthetic dairy wastewater (DWW). Four organic loads (0.5, 1.0, 2.0, and 3.0 kg m–3 d–1 COD) were applied for 45, 95, and 45 days, keeping the HRT at 1 day. Ammonium sulfate and potassium phosphate were added to the DWW (COD:N:P of 500:5:1) and sodium bicarbonate (pH equal to 7.0). UASB1, which received DWW with lactase, showed no difference in COD removal efficiency compared to UASB2, which received DWW without lactase. The average COD removal efficiencies were 69, 77, 70, and 56% for UASB1 and 68%, 72%, 69%, and 57% for UASB2 in each phase. From the Monod kinetics, Y is the growth coefficient (mg mg–1 d–1); Kd is the endogenous decay coefficient (d–1); μmax is the maximum microbial growth rate (d–1); and KS is the limiting substrate concentration (mg L–1) equal to 1.16 and 1.20; 0.05 and 0.04; 0.18 and 0.13; and 248 and 109, respectively, for UASB1 and UASB2. It can be concluded that the analysis of the anaerobic degradation of DWW in the UASB reactor proved to be adequate, with COD removal efficiencies considered satisfactory (70–76%). The application of lactase as a pre-treatment was not effective in increasing the biodegradability of synthetic dairy wastewater.