Effect of calcium ions on fouling properties of alginate solution and its mechanisms

In this study, effect of calcium ions on the filtration behaviors of alginate solution and its underlying mechanisms were systematically investigated. It was found that, the filtration resistance of the formed gel layer and the specific filtration resistance (SFR) of alginate solution showed an unimodal pattern with increase in Ca2+ concentration, and the maximal SFR was as extremely high as 3.63x10(15) m.kg(-1). Series analyses showed that Ca2+ concentration exerted no apparent impact on pore clogging resistance, composition of functional groups and elements of the formed gel. In contrary, increase in Ca2+ concentration caused transitions of colloid formation and alginate polymer micromorphology in solution, well corresponding to the unimodal pattern of filtration behaviors. It was proposed that, Flory-Huggins mechanism governed the extremely high SFR of the alginate gel. Meanwhile, it was suggested that initial calcium binding by alginate occurred in intermolecular rather than intramolecular, which was the key mechanism governing the development of micromorphology and SFR of alginate gel with increase in Ca2+ concentration. These findings offered deep insights into alginate gel fouling associated with calcium ions, and also gave implications to membrane fouling control in membrane bioreactors.