Solar photocatalytic degradation of inherent pharmaceutical residues in real hospital WWTP effluents using titanium dioxide on a CPC pilot scale reactor

Abstract

Hospital wastewaters (HWW) contain a complex mixture of pharmaceutical compounds that cannot be removed by conventional treatment processes. This study reports on the degradation of Pharmaceutical Active Compounds (PhACs) in hospital wastewater treatment plant (WWTP) secondary effluents using TiO2 and solar compound parabolic collector pilot plant. Inherent concentration loadings of pharmaceuticals in secondary wastewater were photocatalytically treated in a ‘’real-world’’ approach. Among the detected pharmaceuticals, amisulpride, venlafaxine and metabolite O-desmethyl venlafaxine, citalopram and carbamazepine occurred in all experimental runs. The analysis of the samples before and after the photocatalytic treatment was accomplished by solid phase extraction, followed by liquid chromatography-Orbitrap high-resolution mass spectrometry. Results showed that photocatalytic degradation of PhAcs followed first order kinetics. Catalyst loadings higher between 150 mgL−1 resulted in removal percentages higher than 73% with accumulative energy c.a. > 25 kJL−1 depending on the initial wastewater characteristics. For 200 mgL−1 catalyst loading pharmaceutical removal rate constants ranged between 0.018 and 0.039 LkJ−1 recorded for citalopram and venlafaxine, respectively. Photocatalytic treatment resulted also in the amelioration of the effluent quality physicochemical characteristics i.e. COD, BOD as well of the biodegradability index. The catalyst reusability was studied without any treatment for three consecutive cycles showing a significant efficiency decrease mainly between the first and the second cycle i.e. from 21% to 80% in the respective reaction constants. Finally, the effluent toxicity before and during the photocatalytic treatment was evaluated by Vibrio fischeri bioassay revealing that toxicity is sharply decreased leading to non-toxicity in the final treated effluents. Further studies on TiO2 photocatalytic applications should focus on the separation and regeneration of catalyst.