Adsorption of bisphenol-s (BPS) from water using activated carbon

Bisphenol-A (BPA) has been linked to numerous health problems. Therefore, Bisphenol-S (BPS) was deemed a suitable replacement for BPA because it has excellent high temperature stability and less toxicity than BPA. Adsorption was the most common technique and widely used method for BPA removal from water due to its comparatively low cost and ease of operation. BPA has a similar structure to BPS; therefore, it is expected to respond well to sportive removal. For this research, the sportive removal of BPS from water was examined under various experimental conditions (carbon dose, contact time, pH, and ionic strength). Carbon dose experiments revealed that as the carbon dose increased, the adsorption capacity decreased. Results showed minimal difference in the adsorption capacities for the 20 mg/L and 30 mg/L PAC doses. In addition, there was no substantial change in adsorption capacity when the contact times were increased from 30 minutes to 3 hours, indicating that equilibrium was reached quickly. In ultrapure water, at pH 7, the adsorption capacity and percent of BPS removal was the highest, whereas at higher pH conditions less BPS sorption occurred. Optimal BPS sorption was achieved when the ionic strength was 0.03 M in ultrapure water, and may be due to the salting out effect decreasing BPS solubility. Further increases in ionic strength resulted in less BPS sorption, suggesting that the ions added were inhibiting BPS-carbon electrostatic interactions. Langmuir and Freundlich adsorption isotherm models were applied to the experimental data. Langmuir and Freundlich isotherms both predicted BPS sorption to the PAC well and yielded R2 values of 0.94-0.98. The R2 values for the Langmuir isotherms were slightly higher than those obtained for the Freundlich isotherm. The isotherm results coupled with the plateau in adsorption capacity observed in the carbon dose experiments appears to indicate that BPS sorption onto this powdered activated carbon can be described best by Langmuir monolayer sorption. The carbon usage rate (CUR) was investigated for a 5.5 mg/L target BPS equilibrium concentration, and despite changes in experimental conditions the CUR remained about 0.02 g PAC/L water treated. In addition, when the target BPS equilibrium concentration changed from 5.5 to 2 ppm, the CUR remained about 0.02 mg PAC/L water treated. This result further supports that monolayer sorption of BPS may be occurring since not further carbon usage occurs when the target equilibrium concentration is decreased. Overall, these results indicate that activated carbon may be a feasible treatment option for removing BPS from water and that electrostatic interactions and monolayer sorption may be the key mechanisms for adsorption on this bituminous-based carbon