Photocatalytic Degradation of Inherent Pharmaceutical Concentration Levels in Real Hospital WWTP Effluents Using g-C3N4 Catalyst on CPC Pilot Scale Reactor.

The objective of this work was to evaluate the efficiency of a solar photocatalytic process using g-C3N4 as photocatalyst on the degradation of pharmaceutical compounds detected in hospital wastewater treatment plant secondary effluents. A compound parabolic collector pilot plant, established in the secondary effluent stream of the Ioannina city hospital wastewater treatment plant, was used for the photocatalytic experiments. The analysis of the samples before and after the photocatalytic treatment was accomplished using solid phase extraction (SPE), followed by UHPLC-LTQ/Orbitrap HRMS. Initial effluent characterization revealed the presence of ten pharmaceutical compounds. Among these, amisulpride, O-desmethyl venlafaxine, venlafaxine and carbamazepine were detected in all experiments. Initial concentrations ranged from 73 ng L-1 for citalopram to 2924.53 ng L-1 for O-desmethyl venlafaxine. The evolution of BOD5 and COD values were determined before and after the photocatalytic treatment. All detected pharmaceuticals were removed in percentages higher than 54% at an optimum catalyst loading ranging between 200 and 300 mg L-1. The potential of the catalyst to be reused without any treatment for two consecutive cycles was studied, showing a significant efficiency decrease.

Study on the photocatalytic degradation of metronidazole antibiotic in aqueous media with TiO2 under lab and pilot scale.

Nowadays, the increased consumption of antibiotics, such as metronidazole (MTZ), leads to their introduction in wastewater as well as in the receiving surface waters due to their incomplete removal by conventional wastewater treatment plants. Heterogeneous photocatalysis is a versatile technology that can efficiently degrade such organic contaminants. In the present research, the photocatalytic degradation of MTZ with TiO2 P25 was studied under lab and pilot (CPC reactor) conditions. The antibiotic was efficiently removed at high rates in both cases (100 % and 91 %) following pseudo-first order kinetics with rate constants equal to 0.0452 min-1 (±RSD% = 0.68 % - 2.57 %) and 0.0462 L KJ-1 (±RSD% = 8.94 % - 21.64 %) respectively. Also, by scavenging lab scale experiments, the contribution of the generated reactive species was investigated and hydroxy radicals (HO•) were proposed as the predominant species. By applying high resolution mass spectrometry techniques, the transformation products (TPs) were identified and possible transformation pathways were proposed. The ecotoxicity of the TPs was assessed in silico using the ECOSAR software with the results revealing that most of them were less toxic than the parent compound. Similarly, the mutagenicity, developmental toxicity and bioconcentration factors of the TPs were predicted by utilizing the T.E.S.T. software and in their majority, were found to be less mutagenic and developmentally toxic than MTZ. The ecotoxicity monitoring with the Vibrio fischeri bioassay in both laboratory and pilot scale experiments indicated that through heterogeneous photocatalysis it is possible to reduce the toxicity of wastewater containing MTZ. Finally, the stability and reusability of the photocatalyst was investigated through three consecutive catalytic cycles with the results showing that the performance of TiO2 decreased after each use. For the heterogeneous photocatalysis with TiO2 to be a "real life" applicable technique, further studies focusing on catalyst regeneration and optimization of the catalytic conditions must be conducted.