Inorganic fouling at quartz: water interfaces in ultraviolet photoreactors: III. Numerical modelling

The goal of the third paper in this series is to present a mathematical model of inorganic fouling of quartz surfaces in ultraviolet (UV) photochemical reactors and to further our understanding of fouling processes. The mathematical model was developed to account for mass, energy and momentum transport in the immediate vicinity of the quartz–water interface. The effects of operating conditions and water composition on fouling were studied by conducting numerical simulations within the range of relevant approach velocities and dissolved constituent concentrations. The numerical simulations showed that fouling processes were governed by the thermal output of the lamps, hydrodynamics and inorganic composition in effluents. The model predicts accumulation of materials with inverse solubilities that will increase in the direction of flow due to the effects of the lamps on the temperature field. Model results indicated that approach velocities of less than approximately 10 cm/s represent an important threshold from the standpoint of the temperature field; systems that are characterized by water chemistry that is conducive to fouling (i.e. near saturation with respect to precipitation reactions) are likely to experience severe precipitation fouling under these conditions. The model also demonstrated that accelerated fouling processes, which have been observed following the addition of iron and aluminum-based chemicals at wastewater treatment facilities, could result in local pH effects upon precipitate formation. The mathematical model was found to be capable of explaining fouling behavior observed in field experiments (longitudinal and radial heterogeneity) and providing insights into fouling mechanisms.