Comparison of NF-like and RO-like thin film composite osmotically-driven membranes—Implications for membrane selection and process optimization

Exploitation of osmotically-driven membrane (OM) technologies and accompanying semi-permeable OM fabrication have become promising topics with numerous potential applications. This paper presents a systematic comparison study of nanofiltration (NF)-like and reverse osmosis (RO)-like thin film composite (TFC) OMs in terms of flux performance and fouling behavior. Major governing mechanisms of OM performance were elucidated and revealed to be related with properties of membrane, draw and feed solutions. Results showed the crucial influence of draw solute reverse diffusion (MICP-Js) on OM water flux. Thus the high-rejection RO-like OMs generally performed better than NF-like counterpart in sodium chloride based osmotic processes. On the other hand, the high permeability of NF-like OMs can achieve higher water flux when proper draw solutes were used to minimize MICP-Js. Fouling tests also suggest that the NF-like TFC OMs tend to be more fouling resistant due to its smooth membrane surface. The current study led to a set of systematic criteria for the selection of osmotically-driven membranes, draw solution and other operational conditions, of which the practicability was further elucidated in potential OM applications.