Metformin Removal from Water Using Fixed-bed Column of Silica-Alumina Composite

Abstract

In the last decade, traces of pharmaceutical and personal care products (PPCPs) in the nano and microgram per litre range have been reported in the water cycle; this includes surface water, wastewater, groundwater, and to a lesser extent drinking-water. Their presence in water, even at low concentrations, has raised concerns among drinking-water regulators, governments and water suppliers, regarding the potential risks to human health from exposure to traces of pharmaceuticals via drinking-water. Metformin (MF) and its transformative product, guanyl-urea, are expected to be present in aquatic environments, due to their global consumption rate. Not surprisingly, guanylurea has also been detected in surface water, groundwater, and drinking water. The toxicological studies showed that availability of MF might cause ecotoxicological effects, which suggests that MF is a potential endocrine disruptor and thus further emphasising the threat this drug could pose to our environment. Thus, many treatment methods have been suggested by many investigators to reduce the high levels of MF. Adsorption with some novel materials, for instance, showed great potential in removing MF from water in the batch processes, while very limited investigation has been done in continuous mode. Therefore, an effective adsorption process should be well implemented with use of efficient adsorbent for MF removal from water. Herein, MF adsorptive removal from water by amorphous silica-alumina (SA) composite was carried out in a fixed-bed column under the influence of various dynamic conditions (i.e., inlet solution pH, initial concentration of MF, initial flow rate, and bed-height). Initially, batch adsorption experiments were conducted to determine the adsorption kinetic parameters. Then, the obtained kinetic parameters were used to investigate the continuous adsorption inside the fixed-bed column. In the column experiments, high adsorption of MF was obtained at low flow rate, high bed height, low influent concentration, and high pH. Breakthrough behavior under the influence of various dynamic parameters was also investigated using the advection-axial dispersion model, incorporating surface and intra-particle diffusion theory to identify the key process parameters controlling the rate of adsorption. Furthermore, the unused bed length (HUNU) approach was also employed to determine the best utilization conditions for the column by correlating the unused bed (inactive zone) fraction (FH) from the column with axial Peclet number (Pex).