Heterogenous photocatalytic degradation kinetics and detoxification of an urban wastewater treatment plant effluent contaminated with pharmaceuticals

Abstract

Degradation kinetics and mineralization of an urban wastewater treatment plant effluent contaminated with a mixture of pharmaceutical compounds composed of amoxicillin (10 mg L1), carbamazepine (5 mg L1) and diclofenac (2.5 mg L1) by TiO2 photocatalysis were investigated. The photocatalytic effect was investigated using both spiked distilled water and actual wastewater solutions. The process efficiency was evaluated through UV absorbance and TOC measurements. A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Lepidium sativum) was performed to evaluate the potential toxicity of the oxidation intermediates. A pseudo-first order kinetic model was found to fit well the experimental data. The mineralization rate (TOC) of the wastewater contaminated with the pharmaceuticals was found to be really slow (t1/2 1⁄4 86.6 min) compared to that of the same pharmaceuticals spiked in distilled water (t1/2 1⁄4 46.5 min). The results from the toxicity tests of single pharmaceuticals, their mixture and the wastewater matrix spiked with the pharmaceuticals displayed a general accordance between the responses of the freshwater aquatic species (P. subscapitata > D. magna). In general the photocatalytic treatment did not completely reduce the toxicity under the investigated conditions (maximum catalyst loading and irradiation time 0.8 g TiO2 L1 and 120 min respectively)