Radiation collector systems comparison in Contaminants of Emerging Concern degradation by solar heterogeneous photocatalysis

9 Wastewater with Contaminants of Emerging Concern (CEC) can be generated from different 10 sources as industry, agriculture and urban and hospital wastes. Heterogeneous Photocatalysis (HP) with 11 TiO 2 is one of the Advanced Oxidation Processes (AOPs) most suitable for water treatment with CEC. In 12 this research, three CEC: Safranin T (SF), 2,4-dichlorophenoxyacetic acid (2,4-D) and Sulfacetamide 13 (SAM) degradation was evaluated by solar-HP in a quartz wall reactor. First, 365 nm wavelength 14 radiation was used and the best operating conditions was determined under the high flow and aeration 15 configuration, obtaining a removal rate of 48.05% for SF, 11.64% for 2,4-D and 6.98 for SAM. Then, 16 under these conditions, SF, SAM and 2,4-D degradation with solar lighting was made on 4 radiation 17 collector systems configurations, Flat Plate Collector (FPC), V Collector (VC), Parabolic Collector (PC) 18 and Compound Parabolic Cylinder Collector (CPC) until reaching the same value of accumulated energy 19 (122.77 kJ m -2 ) finding that the PC had the best performance in the treatment for the three pollutants. Finally, the Collector Impact Ratio Factor (CIRF) for the pollutants was calculated, achieving until 12 21 times degradation for SAM.


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Ethics approval and consent to participate: Not applicable.

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Consent for publications: Not applicable.

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Availability of data and materials: The datasets and materials used and /or analyzed during the current 30 study are available from the corresponding author on reasonable request.

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Competing interests: The authors declare that they have no competing interests.

Introduction
presence in the environment has largely gone unnoticed in terms of distribution and / or concentration 53 (Tanga 2020). These involve a wide range of chemical compounds that are used in daily life, including 54 medicines, personal hygiene products, soaps, surfactants, industrial additives, plasticizers, pesticides and 55 a wide variety of chemical compounds that are present in the environment (Rodil 2019). Many of these 56 pollutants are not eliminated through conventional systems; and, for the most part, correspond to 57 substances not regulated by the environmental authorities. Among the dyes belonging to the CEC group, 58 is Safranin T (SF), which is a biological dye that is frequently used to dye tissues, the detection of 59 structures in eukaryotic and prokaryotic cells and also, it's most common use it is in Gram staining 60 (Aguirre 2012). 2,4-Dichlorophenoxyacetic Acid is one of the most widely used compounds in 61 commercial herbicides, being responsible for causing devastating effects on the environment, especially 62 in aquatic ecosystems and human health. Due to its persistent nature, it is not degraded efficiently by 63 wastewater treatment plants, and it is necessary to use other more effective degradation methods such as

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Advanced Oxidation Processes (AOP) are defined as effective methods for the removal of a 70 large number of persistent contaminants. These make changes in the chemical structure of pollutants until 71 they reach mineralization, transforming organic matter into carbon dioxide and water (Samir 2015). One 72 of the most AOP used is the Heterogeneous Photocatalysis (HP) in wich a semiconductor is irradiated to 73 generate reactive spicies and the greatest used in photocatalytic applications is TiO2, particularly the P-25 74 (Evonik®), because it presented a higher photocatalytic activity, is not toxic, is stable in aqueous 75 solutions and It is not expensive (Bendjama 2018). In photocatalytic process with TiO2 in aerobic 76 environments, when ultraviolet light radiation striking a surface of a semiconductor, this one is capable of 77 generating electron-hole pairs and Reactive Oxygen Species (ROS) such as hydroxyl radicals (•OH), photocatalytic processes with TiO2, in addition to properly locating the catalyst (either dispersed or through the implementation of supports) it is necessary to achieve an efficient exposure to the useful light, 81 to ensure an adequate process, said exposure can be carried out using systems of radiation collectors.

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Globally, various collector designs have been proposed which seek to increase efficiency and reduce the 83 costs of photocatalytic systems for decontamination and water treatment (Zhu 2019). HP with TiO2 as a 84 catalyst uses only the UV fraction of the solar spectrum (direct or diffuse). An important aspect of the 85 collectors is the refractive surface that covers them, since this has the purpose of directing and reflecting 86 the useful light towards the reactor to achieve maximum use of it and avoid unnecessary losses. Among

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Due to the problem that has triggered the generation of CEC, in recent years, proposals have 99 been proposed for the treatment of these compounds through the AOP. Collectors without radiation 100 concentration have been widely used in the HP, the CPC system being one of the most efficient and with 101 the best technology available (Olleros 2013). The HP implementation with TiO2 using sunlight as a 102 radiation medium and using a CPC as a collector has proven to be an adequate system for the degradation   (Table 1) were made with the objective of 125 finding a reactor operating condition that allows the best possible degradation of the contaminant. In the 126 follow of pollutants degradation a spectrophotometer Jenway -7200 series was used. The SF was 127 measured at 520 nm, 2,4-D at 280 nm and SAM at 260 nm ( Figure 4). Table 1. Experimental design to determinate the best operation conditions..

Exp.
Air YES High X X

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TiO2 was dispersed in the system with a concentration of 1 g L -1 (Granda-Ramírez 2017

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For the first stage, Figure 5 shows that SF Dark adsorption showed a 9.8% of contaminant 146 adsorbed in the catalyst, establishing that there is an affinity between SF and TiO2 that favors its 147 degradation. Through the photolysis experiments, a higher degradation of SF at a high flow rate was 148 determined obtaining a removal of 8.68%, while a 2.98% at a low flow rate was obtained. According to 149 the results obtained it was determined that the oxygen presence favors the degradation of the contaminant.

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On the other hand, it was determined that the high flow rate (94.84 mL s -1 ) gives a greater degradation of 151 the contaminant. This flow has a speed 3 times higher compared to the low flow (30.73 mL s -1 ), this

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indicates that the solution to be treated experiences a longer contact time with the radiation which allows 153 a greater degradation and efficiency of the system. Analyzing the flow and aeration parameters, the best 154 operating condition for degradation was provided by the E4 (Table 1)

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Collectors design was made based on the reactor internal (2.1 cm) and external (2.2 cm) diameter 176 and its length (13 cm). For each of the collectors, except for the plane, the corresponding design equations 177 used for each geometry will be presented below.

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In the second stage, using the best conditions in SF degradation (air presence and high flow),

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First, it can be observed that the use of solar radiation collectors improves in significant percentages the 228 chosen molecules photodegradation for this study, since the percentages of degradation increase between For SF, although a degradation of 90.82% was achieved with the CP (Figure 10), its enhancing effect was 231 only 1.89 times since its initial removal with a lamp was 48% under better treatment conditions. On the 232 other hand, when analyzing the behavior of 2,4-D, is why it can be observed that although the effect of 233 the use of collectors improved its degradation between 1.27 and 2.89 times (greater than for SF, Figure   234 10) only achieved a contaminant degradation of 33.66%, this is due to the high stability and low

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To determine the impact of the use of solar collectors, the Collector Impact Ratio Factor (CIRF) was 246 determined by the relationship between the degradation obtained with each collector by the degradation 247 obtained with the system without a collector. A ratio higher than 1 indicates an improvement in the 248 degradation system, less than 1 a decline in degradation, and a ratio equal to 1 indicates that the collector 249 does not affect degradation either positively or negatively ( Figure 11). 250 251 Figure 11. Collector Impact Ratio Factor (CIRF) to SF, 2,4-D and SAM photodegradation using solar 252 radiation.

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254 Figure 11 shows that in general, the use of collectors improved the photocatalytic system used 255 performance (Blanco 2004 andDoménech 2004), observing that the parabolic collector (PC) is the one 256 that most increases the degradation of the 3 pollutants, therefore This geometry type is one of the most widely used generally in solar applications (Maldonado 2015 andOlleros 2013). Analyzing the behavior of each pollutant in the designed collectors, it´s can see that there was the greatest impact for SAM, in collector to 90.82% with the CP (Figure 10). Finally, although the CIRF value for 2,4-D is higher than 264 that of SF, its removal levels are not so high, since around of 33.66% were achieved in the best case.

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( Figures 10 and 11), thus showing the great stability that this molecule has. Finally, it can be said that 266 although the performance of the CP was the best of the 4 collectors designed, actually the difference in 267 their performance is similar in each of the pollutants studied (Figures 10 and 11).