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

Abstract

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 (X0) in the batch reactor was 100±15 mg L−1. During the study the treatment of OMW with initial chemical oxygen demand (S0) concentration between 10 and 1,000 mg COD L−1 was investigated. Maximum specific growth rate (μmax) was reached with 130 mg COD 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 mg COD 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 S0 concentration to specific growth rate (μ) and the biokinetic parameters in these equations were calculated. The most appropriate biokinetic equation was the Haldane model in terms of R2 value and the Haldane equation parameters 0.43 h−1, 45.34 mg L−1, and 207.97 mg L−1 were calculated for μmax, half-saturation constant (Ks) and inhibition constant (Ki), 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 μmax, the most-sensitive parameter of the Haldane model, to 0.22 h−1, the model gave a better fit for all tested conditions.