Computing the effective diffusion coefficient of solutes in a multi-salts solutions during forward osmosis (FO) membrane filtration: Experiments and mathematical modelling

• Published in: Journal of environmental management Vol. 214; pp. 215 - 223
• Main Authors: Liyanaarachchi, S., Muthukumaran, S., Kaiser, Joshua, Rogers, Paul, Shu, Li, Shon, Ho Kyong, Jegatheesan, V.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15.05.2018
• Subjects: Concentration polarisation; Effective diffusion; Forward osmosis; Membranes, Artificial; Organic Chemicals; Osmosis; Reverse osmosis; Seawater; Solutions; Water Purification; Concentration polarisation; Reverse osmosis; Forward osmosis; Effective diffusion; Seawater
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2018.03.002

Diffusion coefficient of solutes through a porous membrane media is different from diffusion coefficient through a free homogenous media. Porosity, tortuosity and the thickness of the membrane significantly affect the diffusion through a specific thickness of a membrane and therefore it is termed as effective diffusion coefficient (Deff) which is lower than the actual diffusion coefficient, D. The Deff of single or dual solutes through a porous membrane layer are well documented but not for multiple salts. Therefore, in this study, single, dual and multiple salt mixtures were passed through a flat sheet cellulose triacetate Forward Osmosis (FO) membrane to obtain a semi-empirical relationship with the Deff and its water flux. This will allow computing the structural coefficient of FO membranes. Research community have spent tremendous efforts in membrane modification to reduce the structural coefficient to improve FO process efficiency. Our finding suggests that optimising the draw solution chemistry can achieve this goal. [Display omitted] •In FO, the effective diffusion coefficient (DC) of a salt is lower than actual DC.•Mutual diffusion, ionic size, charge of solutes affect the DC for mixture of salts.•High concentrations and many solutes in draw solution had high effective DC.•Solute resistivity of SO42− lowered when blended with lower molecular size Cl-.•Structural coefficient, KDDeff, varies with the type of salt and its concentration.