H2O2 based oxidation processes for the treatment of real high strength aqueous wastes

Abstract

This work was aimed at studying the applicability of H2O2-based oxidation processes (namely H2O2/UV, photo-Fenton, and Fenton) for the treatment of six real aqueous wastes. These wastes derived from chemical, pharmaceutical, and detergent production, and were characterised by high COD (chemical oxygen demand) and, in four cases, surfactant concentrations: overall, about 100 tests were conducted. The H2O2/UV and photo-Fenton processes proved to be very effective in COD removal, the efficiency being greater than 70%. The optimal treatment conditions for the H2O2/UV process were: 120 min reaction, H2O2/CODinitial dosage ratio = 1/2; the radiation intensity (up to 2000 W·L-1) revealed to be a crucial factor, especially in the earlier stage of the process (about 40 min): this aspect can be exploited to reduce the costs related to energy consumption. For the photo-Fenton process the following conditions were chosen: Fe2+/H2O2 ratio = 1/30; specific power input = 125 W·L-1; H2O2/CODinitial = 1/2; reaction time = 240 min. Photolytic reactions and the presence of dissolved oxygen revealed to be crucial factors for COD removal. The Fenton process, while showing a moderate efficiency (25% COD removal) in the treatment of high loaded wastewaters, provided excellent results in the treatment of aqueous wastes with high content of surfactants. An average yield removal of 70% for non-ionic surfactants (TAS) and 95% for anionic surfactants (MBAS) was obtained, under the following optimal conditions: Fe2+/H2O2 = 1/4, H2O2/CODinitial ratio = 1, and contact time = 30 min.