Factorial Design for Optimizing and Modeling the Removal of Organic Pollutants from Olive Mill Wastewater Using a Novel Low-Cost Bioadsorbent

Abstract

Low-cost bioadsorbent such as shrimp shell chitin was used for the removal of polyphenols and COD from olive mill wastewater (OMW). In order to achieve a high polyphenols and chemical oxygen demand (COD) removal efficiency and to reduce the number of experiments, two levels of fractional 24 factorial design experiments were carried out. The influence of different experimental parameters such as solution pH, adsorbent concentration, contact time, stirring speed, and their interactions during polyphenols and COD removal were investigated. Optimized values of pH, adsorbent concentration, contact time, and stirring speed were found equal to 12, 10 g/L, 24 h, and 420 rpm/min, respectively. The maximum polyphenol uptake under these experimental conditions reached 69.47%. Whereas the maximum removal of COD achieve 43% in 10 g/L, 12, 24 h, and 80 rpm/min for adsorbent concentration, pH, contact time, and stirring speed as optimal conditions, respectively. The experimental equilibrium data were tested using the Freundlich and Langmuir isotherm models. It was found that adsorption of polyphenols on shrimp shell chitin is well fitted both models. Kinetics of the adsorption process was studied by investigating the pseudo-first-order, pseudo-second-order kinetics, and intraparticle diffusion mechanism and showed that the pseudo-second-order kinetic model provided a better correlation for the experimental data studied in comparison to the pseudo-first-order model and intraparticle diffusion. These results revealed that shrimp shell chitin can be used as an effective and low-cost adsorbent to remove polyphenols and COD from OMW.