The use of Electrocoagulation in Removing Silica from Water
With the rapidly increasing demands on water resources, the freshwater shortage has become an important issue affecting the economic and social development in many countries.
As one of the main technologies for producing freshwater from saline water and other wastewater sources, Reverse Osmosis (RO) has been widely used so far.
The presence of high silica concentrations in some brackish water, however, limits the application of RO desalination due to the potential formation of silica scales that irreversibly deteriorate the membrane material and performance.
On the other hand, 70% of industrial water is used as cooling water. However, cooling water recycling can lead to the concentration of dissolved species to a critical point of precipitation of insoluble mineral salts.
Silica scale is a big technical challenge and a big financial burden for industrial operators since it has a dense and rigid physical form. It can reduce boiler power output by 10-20 % and thermal efficiency by 10%, even plug the pipeline, and increase shutdowns.
Thus, it is urgent to remove silica from cooling water in order to recycle and reuse it.
Electrocoagulation is an effective pretreatment process to remove silica from the source brackish water. The effects of several electrical parameters, including electrode arrangement, current intensity, and hydraulic retention time, were studied based on silica removal efficiency.
Total hardness (TH) and pH reduction is an essential pre-treatment step in water desalination plant (thermal or membrane, especially RO), to minimize precipitation of salts, and reduce operation/maintenance costs.
“It can achieve 75% TH removal rate and pH reduction more than 2.4 degrees, without any acidic addition, resulting in less secondary pollution and huge cost savings”.
With electrocoagulation, for initial concentrations of dissolved silica between 80 mg/L and 200 mg/L, the removal efficiency can increase up to 80%.
The electrocoagulation technique, as brackish groundwater pre-treatment, can improve water quality by reducing (TH, pH, electrical conductivity.
Electrocoagulation is a technically feasible option to reduce silica concentration in cooling towers water. The application of this treatment could help to reduce the huge amount of makeup water usually demanded by cooling processes.