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 mod el of inorganic fouling of quartz surfaces in ultraviolet (UV) photochemica l reactors and to further our understanding of fouling processes. The mathe matical model was developed to account for mass. energy and momentum transp ort in the immediate vicinity of the quartz-water interface. The effects of operating conditions and water composition on fouling were studied by cond ucting numerical simulations within the range of relevant approach velociti es and dissolved constituent concentrations. The numerical simulations show ed that fouling processes were governed by the thermal output of the lamps, hydrodynamics and inorganic composition in effluents. The model predicts a ccumulation of materials with inverse solubilities that will increase in th e direction of flow due to the effects of the lamps on the temperature fiel d. Model results indicated that approach velocities of less than approximat ely 10 cm/s represent an important threshold from the standpoint of the tem perature field; systems that are characterized by water chemistry that is c onducive to fouling (i.e, near saturation with respect to precipitation rea ctions) are likely to experience severe precipitation fouling under these c onditions. 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 effe cts upon precipitate formation. The mathematical model was found to be capa ble of explaining fouling behavior observed in field experiments (longitudi nal and radial heterogeneity) and providing insights into fouling mechanism s. (C) 1999 Elsevier Science Ltd. All rights reserved.