M.Sc Thesis

M.Sc StudentGreenberg Gal
SubjectScale Control Techniques for Augmenting Water Recovery in
Desalination Processes
DepartmentDepartment of Chemical Engineering
Supervisors PROFESSOR EMERITUS Raphael Semiat


The benefits of reverse osmosis purification of secondary treated wastewater to enable unrestricted irrigation usage are widely recognized. However, widespread use of this technology is hindered by the presence of phosphate ions, which can readily precipitate a calcium phosphate deposit, blocking the membrane. The objective of the present research was to investigate techniques for coping with this difficulty.

Three possibilities were studied: control of calcium phosphate scaling using currently available antiscalants, removal of the phosphate by electrochemical deposition of calcium phosphate and calcium carbonate and chemical precipitation of calcium phosphate and calcium carbonate using an MgO bed.

The systematic study of the possibility of reliable calcium phosphate scale control by antiscalants of leading companies, indicated that currently available antiscalants seem to have a rather limited scale control capability over a restricted range of conditions.

The second task was focused on evaluation of a relatively new technique for scale control, based on the precipitation of scaling compounds in the high pH environment prevailing on the cathode of an electrolytic cell. Techniques were developed for characterizing geometrical parameters of the electrolytic cell and for facilitating experimentation. Results indicated that the electrochemical technique has a considerable potential for pretreating wastewater feeds.

The final task performed in this study was exploration of an novel technique for precipitating calcium phosphate and calcium carbonate in wastewaters. The technique consists of contacting feed water with a bed of MgO granules. The alkalinity released by MgO dissolution induces precipitation of phosphates and carbonates scaling compounds. The encouraging results obtained warrant further development of this technique.