Influence of Wastewater DOM Fractions on the Adsorption of Pharmaceuticals onto Activated Carbon

Abstract: Micropollutants in our sources of freshwater is an issue which requires immediate attention. The presence of pharmaceuticals, endocrine disrupting agents, pesticides and other harmful compounds have proven to have impact on the aquatic as well as on human life. Treated wastewater being a major source of ingress of micropollutants into the aquatic environment, the current standards do not stipulate any significant restriction on discharge but focuses on the monitoring. This is majorly due to two reasons, lack of understanding about the different compounds and available treatment options are not fully investigated. Dissolved organic matter (DOM) in the wastewater has proven to have significant impact on the treatment processes designed to remove micropollutants. Even the DOM are less toxic, they often enable transport for various toxic substances such as pharmaceuticals if not treated. In case of activated carbon, DOMs compete with micropollutants for sorption on active sites. Micropollutants have different characteristics and therefore, to optimize these processes, a deeper understanding about the influent along with the treatment process itself is important. This research focus on the elimination of dissolved organic carbon (DOC) based on size exclusion and hydrophobic/hydrophilic fraction and its effect on the removal of pharmaceuticals using activated carbon. In this research, membrane filtration was used to eliminate DOC and based on elimination of different size fractions, the performance of removal of pharmaceuticals using powdered activated carbon was evaluated. It was observed that the effect of DOC on the treatment is not only a function of molecular weight distribution but the presence of hydrophobicity/hydrophilicity in the wastewater. To study this, the wastewater was fractionated to remove hydrophilic and hydrophobic fractions using a rapid fractionation method and the effect of removal of one fraction on the competition for removal of pharmaceuticals was studied. The study affirms the finding by various researchers that the presence of high molecular weight compounds (>25 kDa) does not considerably affects the performance of activated carbon for removal of pharmaceuticals but a significant impact was observed due to the competition by low molecular weight compounds. Another important part of the study was to comprehend the effect of hydrophobicity and hydrophilicity and the study indicates that the presence of hydrophobic compounds contributes to most of the competition with pharmaceuticals for sorption on activated carbon. Furthermore, the study also suggests that the use of DOC concentrations of wastewater to evaluate the dosing requirements of activated carbon for efficient removal of pharmaceuticals may not be a good practice.