Removal Kinetics of Olive-Mill Wastewater in a Batch-Operated Aerobic Bioreactor

This study involves the removal of the olive-mill wastewater (OMW), which is a significant pollutant, in a batch reactor under aerobic conditions by mixed cultures. It also includes comparison of different substrate inhibition models, calculation of kinetic parameters, and testing the merit of the chosen mathematical model with respect to OMW concentration and changes with time. Average initial microorganism concentration ($X_0$) in the batch reactor was $100\pm 15\mathrm{mg}{\mathrm{L}}^{-1}$. During the study the treatment of OMW with initial chemical oxygen demand ($S_0$) concentration between $10\mathrm{and}\mathrm{1,000}\mathrm{mg}\mathrm{COD}{\mathrm{L}}^{-1}$ was investigated. Maximum specific growth rate (${\mu }_{\max }$) was reached with $130\mathrm{mg}\mathrm{COD}{\mathrm{L}}^{-1}$ initial concentration and 3 h experimental duration produced 57.17% chemical oxygen demand (COD) removal efficiency. Other experiments with increasing initial concentration increased COD removal duration, with $927\mathrm{mg}\mathrm{COD}{\mathrm{L}}^{-1}$ initial concentration regressing to 8.88% removal efficiency after 3 h. The biokinetic equations of Aiba, Haldane, Tseng, and Yano and Koga were chosen to relate $S_0$ concentration to specific growth rate ($\mu$) and the biokinetic parameters in these equations were calculated. The most appropriate biokinetic equation was the Haldane model in terms of $R^2$ value and the Haldane equation parameters $0.43{\mathrm{h}}^{-1}$, $45.34\mathrm{mg}{\mathrm{L}}^{-1}$, and $207.97\mathrm{mg}{\mathrm{L}}^{-1}$ were calculated for ${\mu }_{\max }$, half-saturation constant ($K_s$) and inhibition constant ($K_i$), respectively. Also, a mathematical biokinetic model including the Haldane equation was used to test the OMW removal performance and it was seen that the chosen model was well able to reflect system behavior. After the calibration of ${\mu }_{\max }$, the most-sensitive parameter of the Haldane model, to $0.22{\mathrm{h}}^{-1}$, the model gave a better fit for all tested conditions.