Ethanol production from deproteinized cheese whey powder in a batch fermentation process: Optimization of process and kinetic modelling

Cheese whey powder (CWP) is an interesting raw material for bioethanol production, since it is a dried and concentrated form of cheese whey, a dairy wastewater and contains high lactose content along with other nutrients. In order to reduce the production cost and to minimize the harmful effect on the environment, it is advantageous to study the treatment of wastewater containing carbohydrates for use as substrates for ethanol production. In the present study, deproteinized CWP solution was used as fermentation medium for ethanol production using Kluyveromyces marxianus strain NCIM 3217 in batch experiments. The physical parameters of fermentation such as temperature and pH were optimized and were found to be 35 degrees C and 4.5, respectively, for the highest yield of ethanol for 24 h. At the optimized conditions of temperature and pH, the effect of initial sugar concentration (between 150 and 250 g/L) of feed CWP solution was studied for 72 h. Maximum ethanol production of 59.33 g/L was achieved at initial lactose concentration of 200 g/L, and therefore, it could be used as the most appropriate substrate dosage with which optimal production of ethanol and high substrate utilization could be obtained. Above 200 g/L lactose concentration, both biomass and ethanol concentrations were decreased since the hypertonic condition caused by high levels of substrate might has abated the viability and fermentation ability of the yeast. Ethanol fermentation was modelled using unstructured, kinetic models under optimized conditions of temperature and pH to depict the importance of yeast growth, product formation and substrate utilization for all the three lactose concentrations. Monod and Leudeking-Piret equations were used for batch fermentation with regard to lactose utilization and incubation time. The obtained results showed an acceptable fitting of the experimental data to the kinetic models with high significant R-2 values and, therefore, may be applied for the production of ethanol by fermentation of CWP. Biomass yield (Y-X/S), product yield (Y-P/S) and ethanol productivity (Q(P)) were all found to be highest at 200 g/L lactose.