Silica is one of the most dangerous minerals for a membrane and it occurs in water in two different forms. The precaution differs for each.
Silica occurs in water both in colloidal form (as particles) and in dissolved form. The two do not create the same problem and are not removed by the same measure; a precaution taken without that distinction is usually wasted.
Colloidal silica exists in water as particles of very small micron size and passes standard filtration easily. Once it reaches the membrane it accumulates on the surface and forms a layer that is hard to reverse.
The precaution is physical: cartridge filters of 1 micron and below, or an ultrafiltration stage. Ultrafiltration is particularly effective here, because its pore size is far smaller than colloidal silica.
Dissolved silica cannot be retained by a filter; what you have to do is delay its reaching saturation and precipitating on the membrane surface. The chemical that does this is an antiscalant.
The critical point here is selecting an antiscalant suited to the amount of silica in the water. A general-purpose product chosen on the basis of hardness falls short when silica is high. The right choice can only be made with a detailed water analysis and a projection calculation.
Membrane replacement is decided by data, not by the calendar. The five indicators we look at in the field and what each of them means.
View →If hardness appears early at the softener outlet, the problem usually lies not in the resin itself but in the water reaching it and in the regeneration settings.
View →In cooling water it is usually unnecessary to filter the full flow. The points that decide between side-stream and full-stream filtration.
View →Membranes are delicate structures and the cause of fouling is not always the same. The fouling we see in the field falls into three main groups; the remedy changes with that distinction.
View →Read flow and conductivity together and they point to the source of the damage with surprising clarity. Three typical patterns and the problem each one indicates.
View →The cleaning decision looks not at the calendar but at three measurements: differential pressure, permeate conductivity and production flow. The threshold values, and what to do after a long shutdown.
View →An antiscalant is chosen from an analysis, not from a catalogue. The two decisive parameters, and why the projection calculation must not be skipped.
View →The short answer: yes, and irreversibly. Membranes have a low tolerance to chlorine and the damage cannot be undone by cleaning.
View →Activated carbon and SMBS dosing are the two ways of neutralising free chlorine ahead of a membrane. When to prefer which.
View →Let us size the system together; we will survey the site in person if needed.
