Inorganic fouling at quartz:water interfaces in ultraviolet photoreactors—I. Chemical characterization

Fouling of quartz jackets around mercury arc lamps represents a performance limitation in photochemical reactors used in treatment of aqueous streams, such as those used in disinfection, photocatalysis and UV-based advanced oxidation processes. These fouling materials are generally comprised of inorganic constituents, though little is known about their specific chemistry. The goal of this paper is to characterize inorganic fouling on quartz surfaces in photoreactors by evaluation of the composition of fouling materials and chemical analysis of corresponding waters. Results showed that the fouling materials were predominantly amorphous inorganics. Fouling material composition was found to be site-specific. Cation composition in the fouling materials was found to be highly complex, with many metals being common to all samples; in all cases, iron, aluminum and calcium were found to represent the majority of the metals present. Predominant anions included carbonate, sulfate, hydroxide, chloride and phosphate. In the absence of UV radiation and heat from UV lamps, the extent of inorganic fouling was substantially diminished. Thermally-induced precipitation of inorganic species and impaction of preexisting colloidal particles were hypothesized to be the primary mechanisms responsible for inorganic fouling; accumulation of materials due to direct ion exchange reactions with the quartz surfaces was shown to be of negligible importance.