Removal of pharmaceuticals from water: Using liquid-core microcapsules as a novel approach

Abstract

In recent years ever-increasing amounts of pharmaceuticals are being detected in the aquatic environment and in some cases, they have even been discovered in drinking water. Their presence is attributed mainly to the inability of sewage treatment plants to adequately remove these compounds from the sewage influent. The aim of this study was to investigate the feasibility, kinetics and efficiency of using liquid-core microcapsules as a novel methodology, termed capsular perstraction, to remove seven pharmaceuticals commonly found in the environment, from water. The process involves the envelopment of pre-selected organic solvents within a porous hydrogel membrane to form liquid-core microcapsules, which can be used to extract a large range of compounds. Results indicate that this novel approach is capable of extracting the seven chosen compounds rapidly and with a variable efficiency. The simultaneous use of both dibutyl sebacate and oleic acid liquid-core microcapsules at a liquid volume ratio of only 4% (v/v) resulted in the following extractions within 50 min of capsule addition to contaminated water: furosemide 15%; clofibric acid 19%; sulfamethoxazole 22%; carbamazepine 54%; warfarin 80%; metoprolol 90% and diclofenac 100%. The effects of different agitation rates, microcapsule size and membrane thickness on the rate of mass transfer of warfarin into the liquid-core (dibutyl sebacate) of microcapsules was also examined. Results showed that the main rate-limiting step to mass transfer was due to the stagnant organic film (microcapsule size) within the core of the microcapsules. A volumetric mass transfer coefficient of 2.28 × 10 −6 m/s was obtained for the smallest microcapsules, which was nearly 4-fold higher compared to the value (0.6 × 10 −6 m/s) obtained for the largest microcapsules used in this study. Even with this resistance liquid-core microcapsules are still capable of the rapid extraction of the tested compounds and may provide a platform for the safe disposal of the pharmaceuticals after removal.