M.Sc Thesis

M.Sc StudentPinkesfeld Or
SubjectNovel Technique of Electrochemical Removal of Inorganic
DepartmentDepartment of Chemical Engineering
Supervisors PROFESSOR EMERITUS Raphael Semiat
Full Thesis textFull thesis text - English Version


The presence of phosphate in wastewaters and of silica in brackish waters can cause difficulties in water treatment processes. These species can form sparingly soluble salts and preventive measures are essential in order to avoid membrane blockage by scale deposition. The objective of this work was to investigate electrochemical removal of phosphate from secondary treatment effluents and of silica from brackish waters.

Phosphate and silica removals were investigated using a recently developed technique based on an electrochemical cation exchange membrane system (ECM system) developed in our laboratory. The ECM system overcomes major drawbacks of the current electrochemical technology, notably high electrode area requirements. The improved system enables considerable reduction of the cathode area, by a factor as high as 10 to 20.

The parameters investigated in phosphate and silica removal were the effects of current density and pH on the precipitation rate, the fractional removal and the energy requirement. Current densities in the phosphate investigation were varied in the range of 45 to 360 A/m2 and from 100 to 480 A/m2 in the silica investigation. The pH levels were varied from 9.1 to 11.5 in the phosphate investigation and from 10.5 to 12.1 in the silica investigation. The effect of presence or absence of phosphate on calcium carbonate precipitation was studied in the phosphate investigation. The effect of presence or absence of magnesium on silica precipitation was studied in the silica investigation.

Both contaminants were easily removed by the ECM system. Phosphate removal of 87% and silica removal of 92% were readily achieved. The experimental data revealed that the presence of phosphate affected significantly the course of calcium carbonate precipitation. Experimental results confirmed that silica removal is achieved by an adsorptive process involving magnesium hydroxide rather than by a chemical precipitation reaction.

Energy consumption is a major consideration. Phosphate removal was achieved with 0.5 to 3 KWh/m3 solution indicating a potential for viable phosphate removal by the ECM system. The lowest energy consumption for silica removal was found to be 2.4 KWh/m3 solution. This rather high energy level is likely to be reduced to the acceptable level of 0.5-1 KWh/m3 by further developmental research efforts seeking an optimized ECM system.

In conclusion, results of this work extend significantly information on the capabilities of the novel ECM system.