Abstract
In this work, the concentration polarization layer (CPL) of sulphate in a cross-flow membrane system was measured in-situ using Raman microspectroscopy (RM). The focus of this work is to introduce RM as a new tool for the study of mass transfer inside membrane channels in reverse osmosis (RO) and nanofiltration (NF) generally. Specifically, this work demonstrates how to use RM for locally resolved measurement of sulphate concentration in a cross-flow flat-sheet NF membrane flow cell with channel dimensions similar to commonly applied RO/NF spiral wound modules (channel height about 0.7 mm). Concentration polarization profiles of an aqueous magnesium sulphate solution of 10 gsulphate·L−1 were obtained at operating pressure of 10 bar and cross-flow velocities of 0.04 and 0.2 m·s−1. The ability of RM to provide accurate concentration profiles is discussed thoroughly. Optical effects due to refraction present one of the main challenges of the method by substantially affecting signal intensity and depth resolution. The concentration profiles obtained in this concept study are consistent with theory and show reduced CPL thickness and membrane wall concentration with increasing cross-flow velocity. The severity of CP was quantified to reach almost double the bulk concentration at the lower velocity.
Highlights
Www.nature.com/scientificreports improved mass transfer and decreased yield
The results presented in this work were all measured on a fixed position in the middle of the feed channel, 8.5 cm from the inlet
The present work demonstrates the applicability of Raman microspectroscopy (RM) for the measurement of CP in a NF setup representative of commercial spiral wound modules
Summary
Www.nature.com/scientificreports improved mass transfer and decreased yield. Transmembrane pressure (TMP) and membrane characteristics, e.g. permeability and rejection, largely influence the CPF ( locally). Modelling has produced valuable results, the nature of the water, solute and membrane interactions are very complex. Experimental studies providing local solute concentration profiles in membrane channels are very useful for validation of modelling results. Even fewer studies have tried to measure CP in cross-flow conditions and the authors are not aware of a study presenting an experimental setup to quantify the CPL locally in membrane units with general feed channel dimensions and flow velocities present in spiral wound modules[9,10,11]. RM can be used to measure concentrations of Raman active compounds in aqueous solutions, e.g. sulphate in brackish water[14]. Calibrations cannot readily be transferred to another instrument and have to be done with each instrument independently or adjusted[20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
