Development of chitosan beads as an oil adsorbent and its application in household grease traps

Abstract

The purpose of this research was to develop chitosan beads as an oil adsorbent in household grease traps. The results showed that chitosan beads, synthesized from 3% w/v chitosan flakes in 5% v/v acetic acid and formed the beads in 2.0 M NaOH, provided the best characteristics. The white colored beads were slightly hard with maximum average weight and maximum diameter of 0.0925 ± 0.0101 g and 0.67 ± 0.06 cm. respectively. SEM images revealed that the beads had spherical shapes and homogenously distributed pores. The maximum adsorption capacity was 1667.93 ± 39.61 mg/g (83.40 ± 1.98%) at the optimum adsorbent dosage of 10 g/l, initial oil concentration 20 g/l, pH 5 and 303 K with 25 min of contact time. The adsorption was fitted to the Langmuir adsorption isotherm. Our results indicated that the adsorption was monolayer and chemisorption, and Cm increased with increasing temperature. The kinetic study was correlated with the pseudo-second order, and the intraparticle diffusion was the rate controlling step. The adsorption of oil in the household grease trap showed a significant decrease in Fat, Oil & Grease (FOG), Biochemical Oxygen Demand (BOD), and Chemical Oxygen Demand (COD) (p < 0.05), while the pH did not change. Also, oil removal in real wastewater was lower than synthetic oil-in-water due to the competition for the biding sites between oil and other compositions presented in wastewater and the formation of stable micelle droplets by the surfactant. Nevertheless, the values of oil concentration in the household wastewater were lower than the standard limit of domestic discharge in Thailand, whereas the values in the treated wastewater from a noodle shop were over the standard value.