Solar/TiO₂ photocatalytic decomposition of β-blockers atenolol and propranolol in water and wastewater

The photocatalytic conversion of two β-blockers, namely atenolol and propranolol in aqueous TiO₂ suspensions was investigated. Irradiation was provided by a solar simulator equipped with 1kW Xe-OP lamp, while emphasis was given on the effect of catalyst type and loading (50-3000mg/L), substrate concentration (5-30mg/L), initial solution pH (3-10), and the addition of H₂O₂ (0.07-1.4mM) and oxygen on degradation in two matrices (i.e. pure water and treated municipal effluent). Of the various catalysts tested, Degussa P25 was highly active yielding up to about 80% conversion after 120min of reaction. In general, conversion was favored at lower substrate concentrations, near-neutral pH values and in the absence of other organics (i.e. in pure water), while the addition of H₂O₂ did not accelerate kinetics which seem to follow the Langmuir-Hinshelwood model. Toxicity to D. magna was evaluated prior to and after photocatalytic treatment. Toxicity increased during the early stages of the reaction and then progressively decreased upon the elimination of the substrate and its reaction intermediates, with propranolol being more toxic than atenolol.