Modeling and experimental evaluation of vacuum-UV photoreactors for water treatment

Vacuum-UV (VUV) radiation is a promising and effective technology for the oxidation of organic contaminants. The VUV-induced degradation of a model pollutant, Formic Acid (FA), was modeled and experimentally investigated. Experimental work involved an annular flow-through reactor operated in batch mode with complete recycle of the reactants. Ozone-producing low-pressure Hg lamps were used as the source of VUV radiation. FA concentrations of up to 0.55 mmol L-1 were completely degraded after 40 min of irradiation. FA degradation was accompanied by the formation of H2O2 at concentrations of about 0.3 mmol L-1. Kinetic and radiation models were combined with the corresponding mass balances to describe the experimental results. The kinetic model accounted for the most important reactions occurring in the system, including photolysis of water and H2O2, side reactions between radicals, and degradation of FA. The radiation model, which was solved using the Monte Carlo method, described the propagation of photons in the reactor volume and took into account the optical properties of the solution and the emission power of the lamps, obtained by actimometry. Modeling simulations fit experimental data of FA degradation using VUV, H2O2/VUV, and H2O2/UV with a root mean square error of 7.4%. According to modeling and experimental results, the VUV-induced degradation of FA followed an apparent zero order kinetics, a fact that may suggest the reaction was limited by the availability of hydroxyl radicals (HO center dot). (C) 2010 Elsevier Ltd. All rights reserved.