Optimization of treatment of olive mill wastewater for its evaluation as fermentation medium

In this thesis, the potential of olive mill wastewater to be used for citric acid production was investigated after optimization of activated carbon treatment steps performed after overliming. Temperature, amount of activated carbon, contact time and shaking rate were selected as the independent variables in the treatment. An experimental design including 30 experiments was conducted by using central composite design. Modelling the effects of these independent variables on the amount of total phenolic compounds was performed by response surface methodology. Variation of response with the independent variables was defined by quadratic model. According to variance analysis, the linear effects of amount of activated carbon and temperature and also the quadratic effect of the amount of activated carbon on the response were found to be very important. By numeric optimization; 42.01ºC temperature, 6.99 g/100mL amount of activated carbon, 128.55 minutes contact time and 193.99 rpm shaking rate were determined as optimum conditions. 97% phenolic compound and 50% COD reduction were achieved. Treated olive mill wastewater in optimum conditions, was used in the production of citric acid by Y. lipolytica K-168 after supplementation with some nutrients. Maximum citric acid concentrations were obtained as 42.54 g/L, 29.34 g/L and 20.41 g/L in the media containing glycerol, glucose and residual oil, respectively. It was determined that treatment process caused a 4.5 fold increase in citric acid production in glycerol containing medium, while 5.5. and 2 fold increase was observed in the media containing glucose and residual oil, respectively.