Assessing the influence of flow velocity on the in-situ Koc of bisphenol A by adsorption/desorption column experiments

Abstract

The distribution of pollutants between the solid / liquid interface is an important issue in understanding the transport and adsorption of pollutants in the environment Therefore the soil-water partition coefficient (Kd) obtained from batch experiments was often applied to predict the movement of pollutants Since organic pollutants such as bisphenol A (BPA) mainly accumulate on soil organic matter organic carbon-water partition coefficient (Koc) is more suitable than Kd to investigate the sorption phenomenon of organic pollutants Our research group detected the BPA concentration of sediments and pore water and organic carbon content of sediment in the Jishuei River (JS river 急水溪) and Yanshuei River (YS river 鹽水溪) in Tainan to calculate the in-situ Koc We found that in-situ Koc of JS river (13757 L/kg) was much larger than the equilibrium Koc of 778 L/kg which was from batch experiments It was speculated that high water velocity of the JS river caused BPA in pore water to be diluted and unable to reach equilibrium Therefore in this study a mechanical mixing experiment was used to check whether the BPA samples in JS river was in the state of adsorption or desorption and the column experiments were applied to investigate the influence of water velocity on the change of Koc After a 14-day mechanical mixing the change of Koc in the sediments collected from JS river were calculated The in-situ Koc of BPA decreased from 3292 L/kg on day-0 to 1344 L/kg on day-14 and gradually approached the value of the equilibrium batch experiment which means that BPA in the river sediment was in the desorption state In pulse injection column test the Koc decreased when water velocity increased which shows BPA was in adsorption state and harder to distribute on the sediments at higher water velocity On the contrary in the continuous injection column test the Koc values were proportional to the water velocity suggesting that BPA was in desorption state and the desorbed BPA was diluted at a high water velocity resulting in larger Koc values In the absence of BPA background concentration in the feed water the Koc values increase linearly as the pore volume increases By contrast under the feed water containing low concentration of BPA Koc increases with increasing in the pore volume but gradually converges to a constant and reaches dynamic equilibrium Thus this study verifies that flow velocity is the key factor that dominates the in-situ Koc values far greater than the equilibrium Koc value

Date of Award	2020
Original language	English
Supervisor	Wan-Ru Chen (Supervisor)