Removal of pharmaceutical compounds from wastewater secondary effluents by NF/RO membranes

Recent studies have shown the presence of "new" contaminants in the environment, generally detected at trace concentrations. The presence of such substances, which includes many pharmaceuticals, into soil and surface water is primarily due to the discharge of contaminated wastewater by wastewater treatment plants. The analysis of influents and effluents have pointed out the inefficiency of conventional treatments in removing these micropollutants, enhancing the interest for the implementation of advanced treatments. In particular, this study investigates the removal of 10 pharmaceutical compounds with different physicochemical properties from wastewater secondary effluents by two membranes with a molecular weight cut off (MWCO), of 300 Da (NF270) and 200 Da (SelRO® MPS-34), to improve rejections. Different tests were performed to evaluate the effects of feed wastewater pH and transmembrane pressure (TMP) on pharmaceutical rejection. Both membranes were effective in the removal of the selected pharmaceuticals with average rejections of about 90% for a TMP of 5 bar; in addition, the SelRO membrane was tested at pressures of 10 and 20 bar, resulting in average rejections of 93% and 96%, respectively. Rejections of most compounds were greater at a slightly alkaline pH and, under such conditions, a more severe flux decline was reported. Rejection of ionic compounds (diclofenac, triclosan) increased with increasing pH and at a TMP of 5 bar such increase was more relevant. Hydrophilic and neutral compounds (acetaminophen, caffeine, triclosan) were mainly removed by size exclusion and showed rejections which increased with molecular weight and substantially independent from pH. In this case, the removal percentages obtained were not negligible at all also for compounds having a molecular weight lower than the membrane MWCO, presumably due to the presence of a fouling layer. Removal of PCs with high Log Kow value were affected by hydrophobic interactions with the membrane.