Inorganic fouling at quartz:water interfaces in ultraviolet photoreactors: II. Temporal and spatial distributions

Abstract

The second paper of this series has been developed to present the results of a study of the temporal and spatial distributions of fouling materials at quartz–water interfaces in UV photoreactors. Fouling processes were monitored using in situ UV intensity measurements to determine the decrease in optical transmission through quartz jackets during the experiments; chemical analysis of fouling materials and effluents was used to characterize the temporal/spatial distributions of fouling materials. Temporal analyses of fouling materials indicated that fouling was a zero-order process following an induction period. Fouling reactions were found to be capable of causing substantial ( ca. 50%) reductions in local UV intensity within the irradiated zone over a period of 1–28 days, depending on site-specific water characteristics and operating conditions. Increasing accumulation of fouling materials in the longitudinal direction and the observation of zero-order fouling kinetics supported the hypothesis that thermally-induced (co)precipitation plays an important role in the accumulation of fouling materials. A second mechanism, impaction of preexisting particles and quartz surfaces, resulted in heterogeneity in spatial accumulation around quartz jackets. Time-course UV intensity measurements indicated that iron and aluminum-based treatments (e.g. for phosphorous removal) accelerated fouling processes substantially. Fluid shear also played a role in inorganic fouling in that it influenced the agglomeration of colloidal particles. In the absence of radiation from the lamps, lamp jackets were found to foul quickly with organic materials. As compared with inorganic fouling materials, the organic constituents were found to be loosely held to the quartz surface. Illumination of UV lamps was found to rapidly diminish organic accumulation and promote inorganic fouling.