Optimisation of multi-component inorganic salt composition as draw solute for preparation of concentrated tea extract using forward osmosis process

Abstract

This work aims to identify an appropriate food-grade multi-component draw solute composition with enhanced permeate flux and reduced reverse solute flux. This study also highlights the role of the membrane in an efficient FO process. The osmotic properties of selected mixed-salt solutions of magnesium chloride, sodium chloride, sodium sulphate, and potassium chloride were investigated. Based on osmotic pressure, three multi-solute draw solute (DS) compositions were selected for preparation of concentrated tea extract using forward osmosis process. The role of membrane in the efficient membrane process was evaluated by comparing two commercially available hollow fibre forward osmosis membrane. Compared to salts with monovalent ions (such as NaCl and KCl), the SSF of the divalent ions salts (such as MgCl2 and Na2SO4) is reduced by 57.42% due to their larger hydrated radius. The optimised multi-component draw solute performance was compared with single-salt draw solute by maintaining almost the same osmotic pressure. The results of the lab-scale experimental studies revealed that compared to single salt DS (Jw = 17.66 L m−2 h−1 and specific salt flux, SSF = 1.53 g L−1), the identified multi-component DS provides an enhanced permeate flux (16.91 L m−2h−1) with significantly reduced SSF (0.86 g L−1).