Rejection of organic micropollutants from greywater with forward osmosis: A matter of time

Forward osmosis (FO) has popularized lately due to its lower fouling propensity, higher pollutant rejection, and potentially lower energy consumption than other membrane technologies. Greywater (GW) is a good candidate for FO treatment for its further reuse due to its lower organic and solids content than other wastewater streams, but it contains organic micropollutants (OMP) that might pose a risk for its reuse. Seawater (NaCl) is widely used as draw solution, but the use of fertilizers instead offers the advantage of applying the diluted draw solution for irrigation. This study evaluated the performance of FO for GW treatment focusing on OMP rejection, by means of tests with fertilizers or NaCl as draw solutions and deionized water or GW as feed solutions. The main GW constituents were well rejected, except for sodium, which diffused to the draw solution. Excellent OMP rejection was obtained (>95% in most cases, average 98.5% rejection at the end of the experiments), which was influenced by experimental conditions and OMP properties. Highest rejections were observed for negatively charged OMP and for neutral/positive charged OMP with large molecular weight. Feed type and contact time between feed and draw solutions had the biggest influence on OMP rejection, which decreased over time and by using GW instead of deionized water as feed solution. The diluted draw solution proved safe for irrigation water reuse purposes although sodium content could be of concern. Further studies on the contact time between the solutions are required to foster further applications of FO, as it clearly influenced the rejection of OMP, aspect that is crucial for safe water reuse applications.