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Study of benzotriazoles photocatalytic degradation using TiO2 and TiO2/CNT in optimal reactor configurations from the process scale-up and life cycle of photocatalysts point of view

Traditional wastewater treatment plants (WWTPs) are not fully designed to remove low concentrations of toxic pollutants. Therefore, efforts have been directed towards promising advanced oxidation processes (AOPs) such as solar photocatalysis. However, at a wider scale, photocatalysis yet must reach wider prototype-scale application. Accordingly, it must be acceptable from environmental point of view [1], especially when it comes to nanotechnology usage in synthesis of new photocatalysts. Therefore, assessing environmental impact is the most adequate with a life cycle assessment (LCA) due to its engineering approach. Assessment is made based on the energetic and mass balance of the process and it takes into account chemical reactions which allows comprehensive quantification of impacts on the environment [2]. In this paper, eight scenario analyses were presented to improve understanding of advantages and drawbacks related to photocatalytic degradation of 1H-benzotriazole (BT) with two photocatalysts, either titanium dioxide (TiO2) or nanocomposite of TiO2 and carbon nanotubes (CNT) under different parameters. A comparative LCA was performed with a functional unit set as achieving 90% of BT degradation in comparison with the initial concentration. The scenarios were determined in consideration with the following parameters: the photocatalysts, the source of irradiation and the photoreactor. All experiments were performed on laboratory scale in two photoreactor set ups. A flat-plate cascade reactor (FPCR) mimics an outdoor system application which can be implemented at low cost, while compound parabolic collector (CPC) reactor is recognized as the state-of-the art among reactor design. Photocatalytic oxidation was assisted either by UV photocatalytically active TiO2 or UV-VIS photocatalytically active nanocomposite of TiO2 and CNT under two various simulated irradiation spectra. Both photocatalysts were immobilized on fiber glass mesh by sol-gel method [3]. BT was chosen as a pollutant since it has wide application, such as corrosive inhibition in de- icing fluids and it can be found in bleaching, antifogging and antifungal agents. Its residuals were found mainly in aquatic environments in concentrations from nano to microgram per litre [4]. Advantages and drawbacks related to photocatalytic degradation of 1H-benzotriazole (BT) in correlation with different parameters were detected. Furthermore, quantification of given environmental footprints by LCA represents a good base for a decision making in engineering and applying of custom-made photocatalytic solutions.

1H-benzotriazol, titanium dioxide (TiO2), carbon nanotubes (CNT), life cycle assessment (LCA)

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