Biodegradation of whey waste in a continuous stirred-tank bioreactor

Post-production whey has a high concentration of proteins and lactose that has to be decreased 500-fold before disposal in the environment. The paper describes goat whey biodegradation in a continuous stirred tank reactor (CSTR) using a Bacillus licheniformis strain. The data obtained emphasize the effect of excess organic compounds on growth rate. Accordingly, the Luong equation was applied to describe the batch process while accounting for substrate inhibition; the constants vmax = 2.29·10–4 1/s, Km = 4.79 g/dm3, Ki = 6.03 g/dm3, and n = 1.1 were experimentally obtained. According to accepted theory, the continuous process can be expressed using Monod’s equation (only for the rising side of the kinetic graph) in a restricted range of substrate concentrations (for glucose, up to 2.16 g/dm3). The estimated values of the constants were vmax = 8.52·10–5 1/s and Km = 0.45 g/dm3. The selected strain effectively decreased the lactose content in whey. At residence times above 30 h, almost total decrease in lactose content was observed that met the requirements of the Polish Ministry of Environmental Protection. The biodegradation of proteins was much slower, but their content does not greatly influence the required BOD and COD values.