Water disinfection using photosensitizers immobilized on chitosan.

We have designed experiments to test the idea that the photodynamic effect can be used to lower microbial levels in a flow of water using a sensitizer incorporated into a polymeric membrane. We have selected a naturally derived, wettable polymer, chitosan, which can be reinforced with nylon. Photosensitizers of singlet oxygen formation were incorporated into translucent chitosan membranes by adsorption [5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin, p-THPP], by dissolution and casting [5,10,15,20-tetrakis(p-aminophenyl)porphyrin, p-TAPP], and by covalent attachment by reactive dyeing [zinc(II) phthalocyanine tetrasulfonic acid, ZnPcS]. Preliminary evaluation of photomicrobicidal activity in static systems against Escherichia coli revealed some activity in each case, and showed that the phthalocyanine/chitosan membrane was the most effective. A novel photodisinfection reactor was designed and constructed as a model for a large-scale water-flow system. Using the novel reinforced ZnPcS/chitosan membrane as the photosensitizing surface, a significant photokill of E. coli was observed, thus providing proof of concept.