M.Sc Thesis

M.Sc StudentKorenemandel Dikla
SubjectInvestigation of techniques for Reverse Osmosis Concentrate
DepartmentDepartment of Chemical Engineering
Supervisors PROFESSOR EMERITUS Raphael Semiat


Reverse osmosis (RO) is nowadays the prevalent technology for desalinating saline waters but it has not yet reach maturity. There is a wide scope for process improvement that could lead to further cost reductions. The objective of this research   was to develop an improved process for desalinating brackish water enabling higher water recoveries by partial recycling part of the concentrate waste stream.

 Raw feed water usually contains ions of sparingly soluble salts, notably CaSO4 and CaCO3. In order to prevent their precipitation on the membrane from the concentrating brine, inhibiting agents (“anti-scalants“) are dosed to the feed water. The concentrate is therefore a supersaturated solution of these sparingly soluble salts. One way for increasing water recovery is to recycle part of the brine concentrate to the feed, after precipitating the CaSO4 / CaCO3 held in solution by the anti-scalant. However, anti-scalants impart considerable stability to the supersaturated solution.

The major aim of this research was to examine various techniques for precipitating the scaling species from such anti-scalant stabilized supersaturated solutions. The techniques explored were dosage of a coagulant, dosage of an alkali reagent, dosage of a surfactant and seeding. Striking differences were noted between the CaCO3 and the CaSO4 systems.

Preliminary economic calculations were carried out to estimate the benefits of a recycle process enabling increased water recovery through integration of a CaCO3 removal by precipitation. Results obtained show a potential for considerable cost benefits, justifying further R&D work along directions indicated in this study.