Acidification of Lactose in Wastewater

Acidification of lactose in wastewater was conducted in four series of experiments in an upflow reactor to investigate individual effects of hydraulic retention time (HRT) (2-24 h), lactose concentration in wastewater (2-30 g COD/L), pH (4.0-6.5), and temperature (20°-60°C). Optimum acidification was found at pH 5.5 and 55°C. Acidification increased with HRT, but with the decrease of lactose concentration in wastewater. Degradation of lactose followed the Michaelis-Menten model with a maximum specific degradation rate of 4.39 g/g VSS·day and a half-rate concentration of 1.97 g/L. Production of volatile fatty acids, in general, favored lower lactose concentrations and higher pH, but was not sensitive to HRT and temperature. Distribution of individual volatile fatty acids/alcohols was dependent on lactose concentration, pH, and temperature, but less sensitive to HRT. Under most conditions acetate, propionate, and ethanol were the predominant products. Biogas produced under all test conditions was composed of mostly hydrogen and carbon dioxide, but no detectable methane. Sludge yield was estimated as 0.230 ± 0.021 g VSS/g COD.