title: Increasing RO efficiency by chemical-free ion-exchange and Donnan dialysis: Principles and practical implications.
abstract: Ion-exchange (IEX) and Donnan dialysis (DD) are techniques which can selectively remove cations, limiting scaling in reverse osmosis (RO). If the RO concentrate could be recycled for regeneration of these pre-treatment techniques, RO recovery could be largely increased without the need for chemical addition or additional technologies. In this study, two different RO feed streams (treated industrial waste water and simple tap water) were tested in the envisioned IEX-RO and DD-RO hybrids including RO concentrate recycling. The efficiency of multivalent cation removal depends mainly on the ratio of monovalent to multivalent cations in the feed stream, influencing the ion-exchange efficiency in both IEX and DD. Since the mono-to-multivalent ratio was very high in the waste water, the RO recovery could potentially be increased to 92%. For the tap water, these high RO recoveries could only be reached by adding additional NaCl, because of the low initial monovalent to multivalent ratio in the feed. In both cases, the IEX-RO hybrid proved to be most cost-efficient, due to the high current cost of the membranes used in DD. The membrane cost would have to decrease from ±300 €/m² to 10-30 €/m² - comparable to current reverse osmosis membranes - to achieve a comparable cost. In conclusion, the recycling of RO concentrate to regenerate ion exchange pre-treatment techniques for RO is an interesting option to increase RO recovery without addition of chemicals, but only at high monovalent/multivalent cation-ratios in the feed stream.
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, B9000 Ghent, Belgium. Electronic address: marjolein.vanoppen@ugent.be.
authors.forename: Marjolein
authors.initials: M
authors.lastname: Vanoppen
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, B9000 Ghent, Belgium.
authors.forename: Griet
authors.initials: G
authors.lastname: Stoffels
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, B9000 Ghent, Belgium.
authors.forename: Célestin
authors.initials: C
authors.lastname: Demuytere
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, B9000 Ghent, Belgium.
authors.forename: Wouter
authors.initials: W
authors.lastname: Bleyaert
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, B9000 Ghent, Belgium.
authors.forename: Arne R D
authors.initials: AR
authors.lastname: Verliefde
mesh_terms: D000465:Algorithms; D002412:Cations / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification; D060766:Drinking Water / Q000032:analysis / Q000737:chemistry; D007474:Ion Exchange; D007475:Ion Exchange Resins / Q000737:chemistry; D008567:Membranes, Artificial; D008855:Microscopy, Electron, Scanning; D008962:Models, Theoretical; D009995:Osmosis; D015203:Reproducibility of Results; D012965:Sodium Chloride / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000191:economics / Q000295:instrumentation / Q000379:methods*; D062065:Wastewater / Q000032:analysis / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification*; D018508:Water Purification / Q000191:economics / Q000295:instrumentation / Q000379:methods*
chemical_list: D002412:Cations; D060766:Drinking Water; D007475:Ion Exchange Resins; D008567:Membranes, Artificial; D012965:Sodium Chloride; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Brine recycling; Cation-exchange; Donnan dialysis; Process/drinking water production; Reverse osmosis