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

The second paper of this series has been developed to present the results o f a study of the temporal and spatial distributions of fouling materials at quartz-water interfaces in UV photoreactors. Fouling processes were monito red using in situ UV intensity measurements to determine the decrease in op tical transmission through quartz jackets during the experiments; chemical analysis of fouling materials and effluents was used to characterize the te mporal/spatial distributions of fouling materials. Temporal analyses of fou ling materials indicated that fouling was a zero-order process following an induction period. Fouling reactions were found to be capable of causing su bstantial (ca. 50%) reductions in local UV intensity within the irradiated zone over a period of 1-28 days, depending on site-specific water character istics and operating conditions. Increasing accumulation of fouling materia ls 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-cours e UV intensity measurements indicated that iron and aluminum-based treatmen ts (e.g, for phosphorous removal) accelerated fouling processes substantial ly. Fluid shear also played a role in inorganic fouling in that it influenc ed the agglomeration of colloidal particles. In the absence of radiation fr om the lamps, lamp jackets were found to foul quickly with organic material s. As compared with inorganic fouling materials, the organic constituents w ere found to be loosely held to the quartz surface. Illumination of UV lamp s was found to rapidly diminish organic accumulation and promote inorganic fouling. (C) 1999 Elsevier Science Ltd, All rights reserved.