Colloidal surfaces and oligomeric species generated by water treatment chemicals

Properties of water treatment chemicals were investigated by a novel combination of analytical methods. Oligomer distribution, total surface charge, zeta potential and conductivity were evaluated in simulated systems containing highly and moderately basic polyaluminium chlorides, aluminium sulfate (alum), ferric chloride and ferric sulfate. Species were quantified on the basis of mass spectrometric results. Polyaluminium chemicals gave rise to an intensive and completely cationic distribution of mainly Al-13-based oligomers and high surface charges. Both cationic distribution and charge decreased with increase of pH and increased with concentration of the chemical. The other chemicals produced a wider oligomeric distribution of smaller species, including anions. The dimeric form was typical for iron. In the case of the sulfate-containing chemicals, sulfate was present in the majority of oligomers and zeta potentials were stable. For the chemicals without sulfate, pH values needed to be high enough to provide high zeta values. The results can be utilized in the improvement of coagulation and flocculation mechanisms aimed at the removal of bacteria, viruses and other micro organisms, as well as at humic and mineral particles. In addition, semi quantitative information about oligomeric species may be helpful in breaking down cell membranes to support disinfection.