Photocatalytic reactors for treating water pollution with solar illumination: A simplified analysis for n-steps flow reactors with recirculation

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2004.11.010 Byline: Gerd Sagawe (a), Rodolfo J. Brandi (b), Detlef Bahnemann (a), Alberto E. Cassano (b) Keywords: Photocatalysis; Water pollution; Solar irradiation; Recycle reactors; Photonic efficiency; Chemical oxygen demand Abstract: The concentration of dissolved oxygen in water, in equilibrium with atmospheric air (ca. 8ppm at 20[degrees]C), defines the limits of all practical oxidizing processes for removing pollutants in photocatalytic reactors. To solve this limitation, an alternative approach to that of a continuously aerated reactor is the use of a recirculating system with aeration performed after every cycle at the reactor entering stream. As defined by the nature of a single recirculating step (the need of a reactor operation at a rather low concentration range), this procedure results in a very low photonic efficiency (thus requiring a large photon collecting area and consequently increasing the capital cost). The design engineer will have to resort to a series of several reactors with recirculation. This solution may then lead to a very high Photonic Efficiency for the entire process (i.e., a reduced light harvesting area) at the price of an increase in the required capital cost (due to the larger number of reactors). This paper provides a very simple analysis and analytical expressions that can be used to estimate, for a desired degree of degradation, a trade-off solution between a high number of reactors and a very large surface area to collect the solar photons. Author Affiliation: (a) Institut fuer Technische Chemie. Universitaet Hannover Callinstrasse 3, D-30167 Hannover, Germany (b) INTEC Universidad Nacional del Litoral and CONICET, Guemes 3450, 3000 Santa Fe, Argentina Article History: Received 22 June 2004; Revised 19 November 2004; Accepted 22 November 2004 Article Note: (miscellaneous) Communicated by: Associate Editor Gion Calzaferri