Fouling and transport of organic matter in cellulose triacetate forward-osmosis membrane for wastewater reuse and seawater desalination

Abstract

Forward osmosis (FO) can extract water from a solution with a low chemical potential (feed solution, FS) and transport it to a solution with a high chemical potential (draw solution, DS) through natural osmotic pressure. For wastewater reuse via FO, an identifying the foulants and understanding the fouling and transport mechanisms are important. An element-scale spiral-wound FO (SWFO) system and a laboratory-scale FO module tests were conducted with a cellulose triacetate-based FO membrane. Secondary wastewater effluent was used as the FS. To determine the main foulants in FO, the element-scale SWFO was operated at a wastewater plant for 36 d, and a detailed characterization of the foulants (particularly organic matters; OMs) and a membrane autopsy were conducted. The results were verified via a laboratory-scale demonstration. Hydrophilic and large-molecular-weight OMs was the main foulant. It was transported to the DS from the FS through the membrane. The water flux, reverse solute flux, and related parameters (type, concentration, and valence of the draw solute) affected the transport of OMs through the FO membrane. Therefore, further study is needed to develop strategies for reducing the transportation of OMs through the membrane in the wastewater reuse by selecting a suitable draw solute or properly arranging the elements.