Photocatalytic decontamination of pharmaceutical effluent in a double tube reactor by ZnO catalyst. Physico chemical characterization and optimization. 

Photocatalytic decontamination of pharmaceutical effluent in a double tube reactor by ZnO catalyst. Physico chemical characterization and optimization.  | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Photocatalytic decontamination of pharmaceutical effluent in a double tube reactor by ZnO catalyst. Physico chemical characterization and optimization. F. NAITALI, H GHOUALEM This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-162545/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This work focused on the study of the elimination of a non-steroidal anti-inflammatory drug (diclofenac) using heterogeneous photo catalysis as a treatment. The study investigated the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r r = . and volume flow) on the photocatalytic degradation of diclofenac. The analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration. The study showed that: The heterogeneous photo catalytic degradation is influenced by : The concentration of the ZnO catalyst; The concentration of 1.5 g/L gives a better degradation in diclofenac with a percentage of elimination of 52%; The initial concentration of diclofenac; The concentration of 100 mg/L of diclofenac gives a better degradation with a percentage of elimination of 52%; The ratio r = ; The three ratios (1; 5; and 10%) give a total degradation after one hour of treatment; The volume flow rate of 25 mL/s gives a total degradation after one hour of treatment. Optimal conditions for heterogeneous photo-catalysis are : [ZnO] = 1.5 g/L, [diclofenac] = 100 mg/L, Volume flow rate = 25 mL/s For a volume flow rate of 20 mL/s, optimal conditions are met by adding H 2 O 2 . Environmental Engineering Photo degradation drugs double-tube reactor volume flow ZnO H2O2 Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Introduction Water pollution is caused by different categories of chemical and biological toxic substances. Heavy metals, organic dyes, pesticides, drugs such as anti-inflammatory drugs are known to be frequent pollutants that threaten human health and the environment. Diclofenac is an NSAID. It is fairly poorly eliminated, with variable rates of 17 to 70% in treatment plants, which explains its fairly frequent presence in surface waters (Buser and als 1998, Tixier and als 2003). The catastrophic decline of Pakistani white-collar vultures due to kidney failure is believed to be the result of feeding on improperly treated animal carcasses containing diclofenac residues (Oaks ans als 2004). Based on EC50s, anti-inflammatory drugs such as diclofenac, ibuprofen, naproxen or ketoprofen are considered highly toxic to bacteria and toxic to invertebrates and algae (Hernando 2006). Aquatic systems play a major role in the transport and dissemination of drug residues through the water cycle. Thus, it is recognized that wastewater treatment plants (WWTPs) are the main source of dispersion of pharmaceutical compounds for human use in the environment. Photocatalysis appears to be one of the cheapest POAs to be set up to lead to the degradation of organic compounds (Turchi and als 1990, Herrmann 1999), it is a process that is rapidly developing in environmental engineering. This decontamination by photo catalytique process used in research laboratories (Falamarzi 2019, Moles 2020, Majumdar 2020) has found applications in several industrial sectors. The objective of this study is the optimization of operating conditions for the removal of an anti-inflammatory drug in dynamic mode in a double tube reactor. The study focused on the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r= [H 2 O 2 ]/[ZnO] and volume flow) on the photo catalytic degradation of diclofenac. The analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration. Materials And Methods Diclofenac, raw formula C 14 H 10 Cl 2 NNaO 2 , is a member of the non-steroidal anti-inflammatory drug (NSAID) family. The nomenclature of diclofenac according to IUPAC is : Sodium [2-[(2, Dichlorophenyl) amino]phenyl] acetate, molar mass equal to 318.1 g/mol. Its melting temperature is about 280°C. Appearance: White or slightly yellowish crystalline powder, slightly hygroscopic. Solubility: fairly soluble in water, easily soluble in methanol, soluble in 96% ethanol, sparingly soluble in acetone (Pharmacopée Européenne 2008). Diclofenac is a non-steroidal anti-inflammatory drug (NSAID). The reactor used is tubular in shape with an outer diameter of 12 mm, an inner diameter of 10 mm, a length of 175 mm, a width of 195 mm and a volume of 70 mL. The experimental set-up used is shown in Figure .2. The catalyst used during the photo catalytic treatment is zinc oxide (ZnO) (Naitali and Ghoualem 2014, Naitali and Ghoualem 2015, Valizadeh and Azimi 2011). Zinc oxide is an abundant material on earth and is non-toxic. It is also inexpensive unlike other materials. Zinc oxide is a compound insoluble in water but soluble in acids and alcohols. The molar mass of ZnO is 81.38 ± 0.02 g/mol and its melting temperature is 1975 °C. In its natural state, it is ruby red in color and occurs abundantly in ores, while artificially prepared ZnO is colourless or white. For each test, the solution of the pollutant to be treated is put into a beaker with a volume of 1 liter and stirred with a speed of 400 rpm using a mechanical stirrer type WiseStir HS-30D. This solution passes through the reactor with the help of a Heidolph peristaltic pump. A sample is taken every hour during a period of 5 hours to perform a series of physico-chemical analyses. For this; the samples are centrifuged at 2000 rpm for 8 minutes to remove the catalyst. In order to achieve the best NSAID degradation conditions, we have proceeded to the variations of the following parameters : ZnO catalyst concentration: 0.5; 1 and 1.5 g/L. Concentration of diclofenac: 50; 75 and 100 mg/L. Ratio r = ([H₂O₂])/([ZnO]): 1; 5 and 10%. Volume flow rate: 20.5; 22 and 25 mL/s. The physico-chemical parameters monitored are: pH, electrical conductivity, turbidity, surface tension, COD, Nitrites and the concentration of diclofenac. Results And Discussion The study focused on the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r= [H 2 O 2 ]/[ZnO] and volume flow) on the photo catalytic degradation of diclofenac. The analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration. III.1 Influence of the ZnO catalyst concentration The study of heterogeneous photo catalytic degradation was carried out using the ZnO catalyst whose concentrations are (0.5; 1 and 1.5 g/L). The concentration of diclofenac is 100 mg/L. The volume flow rate is 20.5 mL/s. III.1.1 Hydrogen potential (pH) The pH variation during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.3. For the 0.5 g/L ZnO concentration; the pH decreases from 7.22 to 4.1 after 2h of treatment and then increases to 6.79 at t=5h. For the two concentrations of (1 and 1.5 g/L) ZnO; the pH varies very little during treatment (it is between 6.61 and 7.89). The pH influences the charge on the ZnO particles, the size of the aggregates and the positions of the conductance and valence bands. Thus, the ionization state of ZnO varies with pH (Malato. S et al., 2009). At pH values more acidic than PZC (Im. J.K et al., 2012), the ZnO particle will be positively charged and attraction will be enhanced for anionic molecules. III.1.2 Electrical conductivity (EC) The variation of EC during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.4. For the 0.5 g/L ZnO concentration; the EC increases from 28.9 to 213 µS/cm after 2h of treatment, then decreases to 87.1 µS/cm at t=5h. For both concentrations of (1 and 1.5 g/L) ZnO; EC increases from 28.9 to (42.9 and 77.8 µS/cm) respectively at t=5h. The EC of the aqueous solution is mainly related to the presence of ions in the medium. The higher the conductivity, the greater the degradation of diclofenac. III.1.3 Turbidity (Tu) The variation of Tu during the heterogeneous photo-catalytic treatment as a function of the three ZnO concentrations is shown in Figure.5. For a ZnO concentration of 0.5 g/L; turbidity increases from 2.9 to 27.3 NTU at t=4h and then decreases to 10.1 NTU at t=5h. For both concentrations of (1 and 1.5 g/L) ZnO; turbidity increases from 2.9 to (15.1 and 15.7 NTU) respectively at t=5h. Turbidity is an important parameter and is likely to affect the photocatalytic efficiency. Indeed, high turbidity can affect optical properties and hinder light penetration. Some authors have shown that a turbidity lower than 5 NTU would not affect light penetration. Above this value, turbidity would interfere with the optimal use of light [15, 16]. This explains the decrease in the efficiency of photo catalytic treatment when turbidity increases. III.1.4 Surface tension (Ts) The variation of Ts during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.6. For a ZnO concentration of 0.5 g/L; the Ts increases from 56.9 to 70.26 mN/m after 2 hours of treatment. Beyond 2 hours the Ts is constant until the end of the treatment. For ZnO concentrations (1 and 1.5 g/L); Ts increases from 56.9 to (57 and 59.76 mN/m) respectively during treatment. The variations in Ts are explained by the degradation of diclofenac, which leads to the appearance of other molecules, leading to physico-chemical modifications of the solution and the catalyst. This reflects different types of interactions between the solid (ZnO) and the liquid : - Interactions due to London forces, also called dispersive forces. They always take place regardless of the molecules present. - Interactions due to all other types of forces (polar, acid/base, hydrogen bonds, ...). III.1.5 Chemical Oxygen Demand (COD) The variation of COD during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.7. For the three concentrations (0.5; 1 and 1.5 g/L) of ZnO; the COD decreases from 360 to (130, 162 and 116 mg O2/L) respectively. The chemical oxygen demand represents the amount of oxygen consumed by oxidizable materials in the water. The decrease in COD in the presence of the ZnO catalyst is explained by the absorption of light by the catalyst and the production of hydroxyl radicals responsible for the degradation of organic matter. III.1.6 Nitrites The variation of nitrites during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.8. For the ZnO concentration of 0.5 g/L; the nitrite concentration increases from 0.0086 up to 0.0162 mg/L after 4h of treatment and then decreases to 0.0130 mg/L at t=5h. For the concentration of 1 g/L of ZnO; the nitrite concentration increases from 0.0086 to 0.0125 mg/L after 3h of treatment and then decreases to 0.0113 mg/L at t=5h. For 1.5 g/L ZnO concentration; nitrite concentration increases during treatment from 0.0086 up to 0.0195 mg/L. Nitrites can affect the photo catalytic process in several ways : - Radical and hole scavengers which influence the quantum efficiency and thus the oxidation efficiency of the pollutant, - Compete with the drug during adsorption to ZnO. - Capture photons. - Corrosion or alteration of the photocatalyst. - React directly with the photo catalyst (Chong, 2010) : However, it is interesting to recall that the relative effects of these ions on the photo catalytic process can be variable depending on the pH which influences the zwitterionic nature of ZnO. III.1.7 Concentration of diclofenac The variation in concentration during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.9. For the three studied ZnO concentrations (0.5; 1 and 1.5 g/L), the diclofenac concentration decreases to (50.06; 58.65 and 48.11 mg/L) respectively. The performance of the heterogeneous photo-catalytic degradation of diclofenac as a function of the three ZnO concentrations is shown in Figure.10. The concentration of 1.5 g/L of ZnO gives a high percentage removal in diclofenac concentration which is 52%. The presence of more ZnO can lead to the formation of zinc oxide aggregates which finally do not develop a larger ZnO-diclofenac contact surface than in the case of the 1g/L concentration, thus decreasing the percentage of degradation. Increasing the ZnO concentration to 1.5 g/L also leads to the formation of zinc oxide aggregates, but the catalytic surface area increases, leading to an increase in the percentage of degradation. The decrease in efficiency of one ZnO concentration compared to another can be explained by many characteristics. However, characteristics such as specific surface area, charge recombination, interfacial charge transfer dynamics, particle size, crystallinity, pH etc. can have an influence. On the other hand, the activity of a photocatalyst is also influenced by the type of degradation intermediates generated. A study carried out by (Ryu and Choi 2007) has shown that the photo catalytic activity varies according to the pollutant tested. Indeed, by applying a high concentration of ZnO, more photons can be absorbed and therefore more radicals can be formed. In addition, more diclofenac can be adsorbed on the surface of the photo-catalyst. This promotes the degradation of diclofenac. III.2 Influence of diclofenac concentration The study of heterogeneous photo catalytic degradation was carried out with three concentrations of diclofenac (50; 75 and 100 mg/L). The concentration of the ZnO catalyst is 1.5 g/L. The volume flow rate is 20.5 mL/s. III.2.1 Hydrogen potential (pH) The pH variation during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.11. The pH increases from (7.38; 7.26 and 7.22) to (8.37; 8.45 and 7.89) respectively for the three concentrations studied and after 1 hour of treatment and then decreases until the end of treatment. These results can be explained by the competition reactions for the active sites on the surface of ZnO which involves the displacement of OH- ions, thus decreasing the trapping of holes by these hydroxyl ions and reducing the charge separation. Moreover, the occupation of these active sites can lead to the exclusion of organic compounds from the active sites on the surface of the photo-catalyst (Burns 1999). . III.2.2 Electrical conductivity (EC) The EC variation during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.12. For both concentrations (50 and 100 mg/L) of diclofenac; conductivity increases from (22.6 and 28.9 µS/cm) to (99 and 77.8 µS/cm) respectively during treatment. For the concentration of 75 mg/L diclofenac; conductivity increases from 24 to 91.4 µS/cm after 1h of treatment and then decreases to 34.5 µS/cm at t=2h and remains constant. The EC of the aqueous solution is mainly related to the presence of ions in the medium. The results show that the EC value obviously takes a significant part in the degradation of the organic compound. Indeed, the higher the conductivity, the greater the degradation of diclofenac. III.2.3 Turbidity (Tu) The variation of Tu during the heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.13. For the concentration of 50 mg/L diclofenac; turbidity increases from 4.6 up to 32 NTU after 2h above t=2h the Tu is unstable (values are between 13.2 and 18 NTU). For the concentration of 75 mg/L of diclofenac; turbidity increases from 4.1 to 19.8 NTU after 1 hour of treatment and then it varies little (between 8.6 and 10.7 NTU). For 100 mg/L diclofenac concentration; turbidity increases from 2.9 to 15.7 NTU at t=5h. The variation in turbidity during treatment may be due to light-deflecting degradation products. Thus, photo-dismutation of the catalyst may be possible. III.2.4 Surface tension (Ts) The variation of Ts during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.14. For the concentrations studied (50; 75 and 100 mg/L) of diclofenac; fluctuations are observed during treatment. The observed fluctuations in surface tension are explained by the fact that during treatment, the diclofenac molecule is degraded leading to degradation by-products that compete with the parent molecule. This calls for a concentration gradient in the liquid which influences the Solid/Liquid contact surface. One can distinguish the angle at the advance θa which is at the front of the drop or liquid front and the angle at the retreat θr which is at the back and generally, θa>θe>θr (De Gennes 1985, Dussan 1976). The difference between these different angles comes in particular from the roughness and heterogeneity (chemical, morphological ...) of the surface, or the degradation by-products. III.2.5 Chemical oxygen demand (COD) The variation in COD during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.15. For all three concentrations (50; 75 and 100 mg/L) of diclofenac; COD decreases from (130; 250 and 360 mg O2/L) to (32; 90 and 116 mg O2/L) respectively. Chemical Oxygen Demand (COD) represents the amount of oxygen consumed by oxidizable materials in the water. The decrease in COD in the presence of the ZnO catalyst is explained by the absorption of light by the catalyst and the production of the hydroxyl radicals responsible for degradation. Degradation products can also induce different interactions between ZnO and diclofenac, especially in the case of negatively charged compounds at basic pH such as carboxylic acids, which appear in the mechanisms of photo-catalytic degradation. Different diclofenac/ZnO surface interactions could lead to a modified degradation mechanism and thus to different kinetics. III.2.6 Nitrites The variation of nitrites during heterogeneous photocatalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.16. For all three concentrations (50; 75 and 100 mg/L) of diclofenac; the nitrite concentration increases during treatment from (0.0086; 0.0087 and 0.0086 mg/L) to (0.0188; 0.0224 and 0.0195 mg/L) respectively. The increase in nitrite concentration indicates that degradation begins with the breakdown of the nitrogen bond and the cyclic nucleus of diclofenac. III.2.7 Concentration of diclofenac The variation in concentration during heterogeneous photo catalytic treatment is shown in Figure.17. For all three concentrations (50; 75 and 100 mg/L) the concentration of diclofenac decreases during treatment to (29.15; 42.47 and 48.11 mg/L) respectively. The yield of heterogeneous photo-catalytic degradation to diclofenac is shown in Figure.18. The 100 mg/L concentration of diclofenac gives a high percentage of elimination which is 52%. The higher the initial concentration of diclofenac, the greater the efficiency of the photo-catalytic degradation of diclofenac. III.3 Influence of the hydrogen peroxide (H2O2) concentration The study of heterogeneous photo catalytic degradation was carried out using hydrogen peroxide H2O2 whose ratio r = [H2O2]/[ZnO] is (1 ; 5 and 10%). The concentration of diclofenac is 100 mg/L. The catalyst concentration is 1.5 g/L. The volume flow rate is 20.5 mL/s. The results showed that degradation is complete after 1h of treatment for all three r-ratios. These results are confirmed by the absence of the diclofenac absorption peak (274 nm). The absorption spectrum of diclofenac is shown in Figure.19. These results are explained by the effect of hydrogen peroxide on the optical properties of ZnO. A study (Ozgur. U et al., 2005) has shown that in the presence of H 2 O 2 , ZnO has an emission band with a maximum of 3.24 eV and a wide composite band composed of three sub-bands at 2.2 eV; 2.06 eV and 1.8 eV. This promotes the formation of a large amount of OH. Thus, the concentration of hydrogen peroxide causes an increase in the amount of OH. radicals in the medium and therefore the degradation yield increases. It should also be noted that the quantity of the organic pollutant drops abruptly after one hour of treatment. This high efficiency is mainly due to the rapid formation, in large quantities, of OH radicals. which facilitates the attack between a large quantity of the oxidizing agent and diclofenac. III.3.1 Hydrogen potential (pH) The variation of pH during heterogeneous photo catalytic treatment as a function of the three ratios r is shown in Figure.20. For the 1% ratio; the pH decreases from 7.22 to 6.14 after 1 hour of treatment. For both ratios (5 and 10%); the pH increases from 7.22 to (8.23 and 7.41) respectively after 1 hour of treatment. For pH values more acidic than PZC (Im 2012), the ZnO particle will be positively charged and attraction will be favoured for anionic molecules. III.3.2 Electrical conductivity (EC) The variation of EC during heterogeneous photo catalytic processing as a function of the three ratios r is shown in Figure.21. For all three ratios (1; 5 and 10%); EC increases from 28.9 to (43.6; 38.1 and 34.7 µS/cm) respectively after 1 hour of treatment. The EC of the aqueous solution is mainly related to the presence of ions in the medium. The results show that the EC value obviously takes a significant part in the degradation of the organic compound. The increase in electrical conductivity is due to the presence of the degradation compounds of diclofenac. Indeed, the higher the conductivity, the greater the degradation of diclofenac. III.3.3 Turbidity (Tu) The variation of Tu during photo-catalytic treatment as a function of the three ratios r is shown in Figure 22. For all three ratios (1%; 5% and 10%); Tu increases from 2.9 to (9.6; 7.4 and 8.3 NTU) respectively after 1 hour of treatment. Turbidity is an important parameter and is likely to affect the photocatalytic efficiency. Indeed, high turbidity can affect the optical properties and hinder light penetration. This will decrease the absorption of photons by the photocatalyst. III.3.4 Surface tension (Ts) The variation of Ts during heterogeneous photo-catalytic treatment as a function of the three ratios r is shown in Figure.23. For all three ratios (1; 5 and 10%); Ts increases from 56.9 to (58.81; 61.35 and 69.74 mN/m) respectively after 1 hour of treatment. As the surface tension increases, the catalyst is well wetted, which may increase the transfer of liquid/solid material. This increases the photocatalytic efficiency. III.3.5 Nitrites The variation of nitrites during heterogeneous photocatalytic treatment as a function of the three ratios r is shown in Figure.24. For all three ratios (1; 5 and 10%); nitrite increases from 0.0086 to (0.0227; 0.0097 and 0.0267 mg/L) respectively after 1 hour of treatment. The increase in nitrite concentration indicates that degradation begins with the breakdown of the nitrogen bond and the cyclic nucleus of diclofenac. III.4 Influence of volume flow rate The study of heterogeneous photo catalytic degradation was performed at three volume flow rates (20.5; 22 and 25 mL/s). The concentration of diclofenac is 100 mg/L. The catalyst concentration is 1.5 g/L. The results showed that the degradation is complete for the volume flow rate 25 mL/s after 1h of treatment. This result is confirmed by the absence of the diclofenac absorption peak (274 nm). The absorption spectrum of diclofenac for the 25 mL/s volume flow rate is shown in Figure.25. III.4.1 Hydrogen potential (pH) The variation of pH during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.26. For both volume flows (20.5 and 22 mL/s); the pH increases from 7.22 to (7.89 and 8.73) respectively at t=1h and then varies little. For the volume flow rate of 25 mL/s, the pH increases from 7.22 to 8.25 after 1h of treatment. The increase in pH is due to competition reactions for the active sites on the surface, which involves the displacement of OH- ions, thus reducing the trapping of holes by these hydroxyl ions and reducing charge separation. Moreover, the occupation of these active sites can lead to the exclusion of organic compounds from the active sites on the surface of the photo-catalyst [18]. III.4.2 Electrical conductivity (EC) The variation of EC during heterogeneous photocatalytic treatment as a function of the three volume flows is shown in Figure 27. For the volume flow rate of 20.5 mL/s; the EC increases from 28.9 to 74.5 µS/cm after 3 hours of treatment; beyond 1 hour the EC varies little. For a volume flow rate of 22 mL/s; EC increases from 28.9 to 51.6 µS/cm after 1h of treatment, then decreases to 38.2 at t=2h, after 2h it varies little. For a volume flow rate of 25 mL/s; EC increases from 28.9 to 40.1 µS/cm after 1 hour of treatment. The electrical conductivity of the aqueous solution is mainly related to the presence of ions in the medium. The results show that the EC value obviously takes a significant part in the degradation of the organic compound. Indeed, the higher the conductivity, the greater the degradation of diclofenac. III.4.3 Turbidity (Tu) The variation of Tu during the heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.28. For volume flow rate of 20.5 mL/s; Tu increases from 2.9 to 15.7 NTU at t=5h. For volume flow rate of 22 mL/s; Tu increases from 2.9 to 37 NTU at t=5h. For volume flow rate of 25 mL/s; Tu increases by 2.9 NTU to 33.1 NTU after 1h of treatment. High turbidity can affect the optical properties and hinder light penetration. This will decrease the absorption of photons by the photocatalyst. Some authors have shown that a turbidity lower than 5 NTU would not affect light penetration. Above this value, turbidity would interfere with optimal use of light (Fernandez-Ibanez 2009, Gelover 2006, Chong 2010). This explains the decrease in the efficiency of photo catalytic treatment when turbidity increases. III.4.4 Surface tension (Ts) The variation of Ts during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.29. For a volume flow rate of 20.5 mL/s; Ts varies little (between 56.9 and 59.76 mN/m). For a volume flow rate of 22 mL/s; Ts decreases from 56.9 mN/m to 40.97 mN/m at t=4h and then increases to 64.96 mN/m at t=5h. For the volume flow rate of 25 mL/s; Ts increases from 56.9 to 62.31 mN/m after 1h of treatment. The surface tension of the solutions is lower than that of pure water (72 mN/m). The interaction between the phases in a reactor depends on the velocity and physico-chemical properties of the fluid phases, as well as the geometric and physico-chemical properties of the solid particles. It is important to note that the contact surface between phases, which itself depends on the surface tension, varies according to the flow regime. III.4.5 Chemical Oxygen Demand (COD) The variation of COD during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.30. For both volume flow rates (20.5; 22 mL/s); COD decreases from 360 to (116 and 15 mg O2/L) respectively during treatment. For the 25 mL/s volume flow rate, COD decreases from 360 to 15 mg O2/L after 1 hour of treatment. Chemical Oxygen Demand (COD) represents the amount of oxygen consumed by oxidizable materials in the water. The decrease in COD in the presence of the ZnO catalyst is explained by the absorption of light by the catalyst and the production of hydroxyl radicals responsible for degradation. It can be seen that the rate of mineralization is rapid at the beginning of the treatment and then it decreases. Indeed, at the beginning of the treatment, the mother molecule and its degradation products are more easily oxidized by hydroxyl radicals leading to the formation of aliphatic compounds like carboxylic acids... (Oturan, 2000, Brillas 2003, Boye 2002, Diagne, 2007) that resist well to mineralization by these same radicals. III.4.6 Nitrites The variation of nitrites during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.31. For both volume flow rates (20.5; 22 mL/s); the nitrites increase from 0.0086 to (0.0195; 0.0178 mg/L) respectively after 5h of treatment. For the volume flow rate 25 mL/s, nitrite increases from 0.0086 to 0.0109 mg/L at t=1h. The increase in nitrite concentration indicates that degradation begins with the breakdown of the nitrogen bond and the cyclic nucleus of diclofenac. Nitrites can affect the photocatalytic process in several ways: - Radical and hole traps which influence the quantum efficiency and thus the oxidation efficiency of the pollutant, - Compete with the drug during adsorption to ZnO, - Capturing photons - Corrosion or alteration of the photocatalyst - React directly with the photo catalyst (Chong 2010). However, it is interesting to recall that the relative effects of these ions on the photo catalytic process can be variable as a function of the pH, which influences the zwitterionic nature of ZnO. III.4.7 Concentration of diclofenac The variation in concentration during the heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.32. For both volume flow rates (20.5; 22 mL/s) the diclofenac concentration decreases to (48.11; 24.56 mg/L) respectively during treatment. For the volume flow rate 25 mL/s, the diclofenac concentration decreases from 100 to 12.35 mg/L after 1 hour of treatment. The photo-catalytic degradation performance of diclofenac as a function of the three flow rates is shown in Figure.33. The volume flow rate of 25 mL/s gives the highest removal percentage (100%). The increase in degradation yield with increasing flow rate is explained by : The thickness of the absorbent layer of the treated fluid varies along the reactor. Indeed, at the reactor inlet, the conversion is null x = 0, and the absorbent layer consists only of ZnO. In this case, the majority of the photons are absorbed by the ZnO. Then along the reactor, the conversion progresses and the layer becomes depleted in diclofenac and, conversely, it becomes enriched in degradation compounds. The photons are then absorbed by both ZnO and degradation compounds. The distribution of the absorbed photons between ZnO and the degradation compounds will depend on the hydrodynamic conditions of the reactor. The hydrodynamic regime is defined by the Reynolds number. Table 1 regroups the Reynolds number for the three volume flows studied. Table 1. The Reynolds number for the different volume flows. ρ (Kg/m 3 ) 10 3 µ (Pa.s) 10 -3 V (mL/s) 20.5 22 25 Re 2611 2802 3184 For both volume flows (20.5 and 22 mL/s) the regime is transient. For the volume flow rate of 25 mL/s the regime is turbulent. For a given Reynolds number, the efficiency of photo-catalysis is influenced by : - The amount of material passing through the reactor. - The residence time 𝜏𝑠 of the molecules in the reactor. - The light power. The flux density of incident photons will play on the local speed of the photochemical reaction, which can impact the local and average characteristic times in the zone of illuminated fluid. Conclusion This work focused on the study of the elimination of a non-steroidal anti-inflammatory drug (diclofenac) using heterogeneous photo catalysis as a treatment. The study investigated the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r=[H 2 O 2 ]/[ZnO] and volume flow) on the photocatalytic degradation of diclofenac. The analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration. The heterogeneous photo catalytic degradation is influenced by : -The concentration of the ZnO catalyst. The concentration of 1.5 g/L gives a better degradation in diclofenac with a 52% removal percentage. -The initial concentration of diclofenac. The concentration of 100 mg/L of diclofenac gives a better degradation with a percentage of elimination of 52%. -The ratio r =([H 2 O 2 ])/([ZnO]). The three ratios (1; 5 and 10%) give a total degradation after one hour of treatment. -The volume flow rate. The volume flow rate of 25 mL/s gives a total degradation after one hour of treatment. Optimal conditions for heterogeneous photo-catalysis are : [ZnO] = 1.5 g/L, [diclofenac] = 100 mg/L, volume flow rate = 25 mL/s. For a volume flow rate of 20 mL/s, optimal conditions are achieved by adding H 2 O 2 . Declarations Ethics approval and consent to participate Not applicable Consent for publication Not applicable Availability of data and materials The results and materials presented in this article are realized in the laboratory of Laboratory of Electrochemistry-Corrosion, Metallurgy and Inorganic Chemistry. Faculty of Chemistry. University of Sciences and Technology. Houari Boumediene. Box N°32 El-Alia. Bab-Ezzouar. Algiers. Algeria. The data tables are presented in different forms in the manuscript and are available from the authors. Competing interests The authors Fateh Naitali and Hafida Ghoualem declare that they have no competing interests Funding The authors Fateh Naitali and Hafida Ghoualem received no specific funding for this work Authors' contributions Author Fateh Naitali was a major contributor in working and writing the manuscript. Author Hafida Ghoualem was a major contributor in working and writing the manuscript. Acknowledgements Not applicable Conflict of Interest The authors Fateh Naitali and Hafida Ghoualem declare that they have no competing financial interests There are no competing interests related to this work There are no known conflicts of interest associated with this publication References Boye B, Dieng M. M, Brillas E (2002) Degradation of herbicide 4-chlorophenoxyacetic acid by advanced electrochemical oxidation methods. Environmental Science & Technology 36 3030-3035. Brillas E, Banos M. A, Garrido J. 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Tixier C, Singer H.P, Oellers S, Muller S.R (2003) Occurence and fate of carbamazépine, clofibric acid, diclofenac, ibuprofen, ketoprofen and naproxen in surface waters. Environ Sci Techol 37 1061- 1068. Turchi C.S, Ollis D.F (1990) Photocatalytic degradation of organic water contaminants: mechanisms involving hydroxyl radical attack. J. Catal 122 .178-192. Valizadeh H, Azimi A.A (2011) ZnO/MgO containing ZnO nanoparticles as a highly effective heterogeneous base catalyst for the synthesis of 4 H -pyrans and coumarins in [bmim]BF 4 . JICS 8, 123–130. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-162545","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":9203668,"identity":"3ab17fcf-9b72-4f90-bfc7-b7dcf9afca12","order_by":0,"name":"F. 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rate.","description":"","filename":"f29.jpg","url":"https://assets-eu.researchsquare.com/files/rs-162545/v1/b513907d0ec4b6a67dc983bf.jpg"},{"id":5379651,"identity":"89ae7217-78d2-4b40-907f-0363fbe55348","added_by":"auto","created_at":"2021-01-29 17:13:27","extension":"jpg","order_by":30,"title":"Figure 30","display":"","copyAsset":false,"role":"figure","size":51047,"visible":true,"origin":"","legend":"Variation of COD during heterogeneous photo-catalysis as a function of volume flow rate.","description":"","filename":"f30.jpg","url":"https://assets-eu.researchsquare.com/files/rs-162545/v1/35a7b28df035c6a1c907e649.jpg"},{"id":5379661,"identity":"8594ed8d-6c4b-4508-a6c3-d6861ec373f5","added_by":"auto","created_at":"2021-01-29 17:13:28","extension":"jpg","order_by":31,"title":"Figure 31","display":"","copyAsset":false,"role":"figure","size":52452,"visible":true,"origin":"","legend":"Variation of nitrites during heterogeneous photolysis as a function of volume flow rate.","description":"","filename":"f31.jpg","url":"https://assets-eu.researchsquare.com/files/rs-162545/v1/e6bae299b083eba7c1d107a7.jpg"},{"id":5379658,"identity":"ecf8f8bb-289c-4faa-92e8-fdaa0d2ad0ff","added_by":"auto","created_at":"2021-01-29 17:13:28","extension":"jpg","order_by":32,"title":"Figure 32","display":"","copyAsset":false,"role":"figure","size":43684,"visible":true,"origin":"","legend":"Variation in diclofenac concentration during heterogeneous photo-catalysis.","description":"","filename":"f32.jpg","url":"https://assets-eu.researchsquare.com/files/rs-162545/v1/22440d6790b1e41efb683cac.jpg"},{"id":5379657,"identity":"3417e362-0094-4a39-b94b-99ea5152d464","added_by":"auto","created_at":"2021-01-29 17:13:28","extension":"jpg","order_by":33,"title":"Figure 33","display":"","copyAsset":false,"role":"figure","size":35390,"visible":true,"origin":"","legend":"Heterogeneous photo-catalytic degradation efficiency of diclofenac concentration as a function of volume flow rate.","description":"","filename":"f33.jpg","url":"https://assets-eu.researchsquare.com/files/rs-162545/v1/b299283dddb74f27a2a0c4ab.jpg"},{"id":13653201,"identity":"a671631a-a938-4f40-9017-c9c2fa4fc1d7","added_by":"auto","created_at":"2021-09-17 09:52:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1372735,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-162545/v1/22c2c3f0-c044-4f85-8183-d1fa0eb69149.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003ePhotocatalytic decontamination of pharmaceutical effluent in a double tube reactor by ZnO catalyst. Physico chemical characterization and optimization.\u0026nbsp;\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWater pollution is caused by different categories of chemical and biological toxic substances. Heavy metals, organic dyes, pesticides, drugs such as anti-inflammatory drugs are known to be frequent pollutants that threaten human health and the environment.\u003c/p\u003e\n\u003cp\u003eDiclofenac is an NSAID.\u003c/p\u003e\n\u003cp\u003eIt is fairly poorly eliminated, with variable rates of 17 to 70% in treatment plants, which explains its fairly frequent presence in surface waters (Buser and als 1998, Tixier and als 2003).\u003c/p\u003e\n\u003cp\u003eThe catastrophic decline of Pakistani white-collar vultures due to kidney failure is believed to be the result of feeding on improperly treated animal carcasses containing diclofenac residues (Oaks ans als 2004).\u003c/p\u003e\n\u003cp\u003eBased on EC50s, anti-inflammatory drugs such as diclofenac, ibuprofen, naproxen or ketoprofen are considered highly toxic to bacteria and toxic to invertebrates and algae (Hernando 2006).\u003c/p\u003e\n\u003cp\u003eAquatic systems play a major role in the transport and dissemination of drug residues through the water cycle.\u003c/p\u003e\n\u003cp\u003eThus, it is recognized that wastewater treatment plants (WWTPs) are the main source of dispersion of pharmaceutical compounds for human use in the environment.\u003c/p\u003e\n\u003cp\u003ePhotocatalysis appears to be one of the cheapest POAs to be set up to lead to the degradation of organic compounds \u0026nbsp;(Turchi and als 1990, Herrmann 1999), it is a process that is rapidly developing in environmental engineering.\u003c/p\u003e\n\u003cp\u003eThis decontamination by photo catalytique process used in research laboratories \u0026nbsp;(Falamarzi 2019, Moles 2020, Majumdar 2020) has found applications in several industrial sectors.\u003c/p\u003e\n\u003cp\u003eThe objective of this study is the optimization of operating conditions for the removal of an anti-inflammatory drug in dynamic mode in a double tube reactor.\u003c/p\u003e\n\u003cp\u003eThe study focused on the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r= [H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e]/[ZnO] and volume flow) on the photo catalytic degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003eThe analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration.\u003c/p\u003e"},{"header":"Materials And Methods","content":"\u003cp\u003eDiclofenac, raw formula C\u003csub\u003e14\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eNNaO\u003csub\u003e2\u003c/sub\u003e, is a member of the non-steroidal anti-inflammatory drug (NSAID) family.\u003c/p\u003e\n\u003cp\u003eThe nomenclature of diclofenac according to IUPAC is :\u003c/p\u003e\n\u003cp\u003eSodium [2-[(2, Dichlorophenyl) amino]phenyl] acetate, molar mass equal to 318.1 g/mol. Its melting temperature is about 280\u0026deg;C.\u003c/p\u003e\n\u003cp\u003eAppearance: White or slightly yellowish crystalline powder, slightly hygroscopic.\u003c/p\u003e\n\u003cp\u003eSolubility: fairly soluble in water, easily soluble in methanol, soluble in 96% ethanol, sparingly soluble in acetone (Pharmacop\u0026eacute;e Europ\u0026eacute;enne 2008).\u003c/p\u003e\n\u003cp\u003eDiclofenac is a non-steroidal anti-inflammatory drug (NSAID).\u003c/p\u003e\n\u003cp\u003eThe reactor used is tubular in shape with an outer diameter of 12 mm, an inner diameter of 10 mm, a length of 175 mm, a width of 195 mm and a volume of 70 mL. The experimental set-up used is shown in Figure .2.\u003c/p\u003e\n\u003cp\u003eThe catalyst used during the photo catalytic treatment is zinc oxide (ZnO) (Naitali and Ghoualem 2014, Naitali and Ghoualem 2015, Valizadeh and Azimi 2011).\u003c/p\u003e\n\u003cp\u003eZinc oxide is an abundant material on earth and is non-toxic.\u003c/p\u003e\n\u003cp\u003eIt is also inexpensive unlike other materials.\u003c/p\u003e\n\u003cp\u003eZinc oxide is a compound insoluble in water but soluble in acids and alcohols. The molar mass of ZnO is 81.38 \u0026plusmn; 0.02 g/mol and its melting temperature is 1975 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003eIn its natural state, it is ruby red in color and occurs abundantly in ores, while artificially prepared ZnO is colourless or white.\u003c/p\u003e\n\u003cp\u003eFor each test, the solution of the pollutant to be treated is put into a beaker with a volume of 1 liter and stirred with a speed of 400 rpm using a mechanical stirrer type WiseStir HS-30D.\u003c/p\u003e\n\u003cp\u003eThis solution passes through the reactor with the help of a Heidolph peristaltic pump. A sample is taken every hour during a period of 5 hours to perform a series of physico-chemical analyses.\u003c/p\u003e\n\u003cp\u003eFor this; the samples are centrifuged at 2000 rpm for 8 minutes to remove the catalyst.\u003c/p\u003e\n\u003cp\u003eIn order to achieve the best NSAID degradation conditions, we have proceeded to the variations of the following parameters :\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; ZnO catalyst concentration: 0.5; 1 and 1.5 g/L.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; Concentration of diclofenac: 50; 75 and 100 mg/L.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; Ratio r = ([H₂O₂])/([ZnO]): 1; 5 and 10%.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; Volume flow rate: 20.5; 22 and 25 mL/s.\u003c/p\u003e\n\u003cp\u003eThe physico-chemical parameters monitored are: pH, electrical conductivity, turbidity, surface tension, COD, Nitrites and the concentration of diclofenac.\u003c/p\u003e"},{"header":"Results And Discussion","content":"\u003cp\u003eThe study focused on the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r= [H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e]/[ZnO] and volume flow) on the photo catalytic degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003eThe analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1 Influence of the ZnO catalyst concentration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study of heterogeneous photo catalytic degradation was carried out using the ZnO catalyst whose concentrations are (0.5; 1 and 1.5 g/L). The concentration of diclofenac is 100 mg/L. The volume flow rate is 20.5 mL/s.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1.1 Hydrogen potential (pH)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe pH variation during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.3.\u003c/p\u003e\n\u003cp\u003eFor the 0.5 g/L ZnO concentration; the pH decreases from 7.22 to 4.1 after 2h of treatment and then increases to 6.79 at t=5h.\u003c/p\u003e\n\u003cp\u003eFor the two concentrations of (1 and 1.5 g/L) ZnO; the pH varies very little during treatment (it is between 6.61 and 7.89).\u003c/p\u003e\n\u003cp\u003eThe pH influences the charge on the ZnO particles, the size of the aggregates and the positions of the conductance and valence bands. Thus, the ionization state of ZnO varies with pH (Malato. S et al., 2009).\u003c/p\u003e\n\u003cp\u003eAt pH values more acidic than PZC (Im. J.K et al., 2012), the ZnO particle will be positively charged and attraction will be enhanced for anionic molecules.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1.2 Electrical conductivity (EC)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of EC during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.4.\u003c/p\u003e\n\u003cp\u003eFor the 0.5 g/L ZnO concentration; the EC increases from 28.9 to 213 \u0026micro;S/cm after 2h of treatment, then decreases to 87.1 \u0026micro;S/cm at t=5h.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor both concentrations of (1 and 1.5 g/L) ZnO; EC increases from 28.9 to (42.9 and 77.8 \u0026micro;S/cm) respectively at t=5h.\u003c/p\u003e\n\u003cp\u003eThe EC of the aqueous solution is mainly related to the presence of ions in the medium.\u003c/p\u003e\n\u003cp\u003eThe higher the conductivity, the greater the degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1.3 Turbidity (Tu)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Tu during the heterogeneous photo-catalytic treatment as a function of the three ZnO concentrations is shown in Figure.5.\u003c/p\u003e\n\u003cp\u003eFor a ZnO concentration of 0.5 g/L; turbidity increases from 2.9 to 27.3 NTU at t=4h and then decreases to 10.1 NTU at t=5h.\u003c/p\u003e\n\u003cp\u003eFor both concentrations of (1 and 1.5 g/L) ZnO; turbidity increases from 2.9 to (15.1 and 15.7 NTU) respectively at t=5h.\u003c/p\u003e\n\u003cp\u003eTurbidity is an important parameter and is likely to affect the photocatalytic efficiency. Indeed, high turbidity can affect optical properties and hinder light penetration.\u003c/p\u003e\n\u003cp\u003eSome authors have shown that a turbidity lower than 5 NTU would not affect light penetration.\u003c/p\u003e\n\u003cp\u003eAbove this value, turbidity would interfere with the optimal use of light [15, 16]. This explains the decrease in the efficiency of photo catalytic treatment when turbidity increases.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1.4 Surface tension (Ts)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Ts during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.6.\u003c/p\u003e\n\u003cp\u003eFor a ZnO concentration of 0.5 g/L; the Ts increases from 56.9 to 70.26 mN/m after 2 hours of treatment. Beyond 2 hours the Ts is constant until the end of the treatment.\u003c/p\u003e\n\u003cp\u003eFor ZnO concentrations (1 and 1.5 g/L); Ts increases from 56.9 to (57 and 59.76 mN/m) respectively during treatment.\u003c/p\u003e\n\u003cp\u003eThe variations in Ts are explained by the degradation of diclofenac, which leads to the appearance of other molecules, leading to physico-chemical modifications of the solution and the catalyst.\u003c/p\u003e\n\u003cp\u003eThis reflects different types of interactions between the solid (ZnO) and the liquid :\u003c/p\u003e\n\u003cp\u003e- Interactions due to London forces, also called dispersive forces. They always take place regardless of the molecules present.\u003c/p\u003e\n\u003cp\u003e- Interactions due to all other types of forces (polar, acid/base, hydrogen bonds, ...).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1.5 Chemical Oxygen Demand (COD)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of COD during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.7.\u003c/p\u003e\n\u003cp\u003eFor the three concentrations (0.5; 1 and 1.5 g/L) of ZnO; the COD decreases from 360 to (130, 162 and 116 mg O2/L) respectively.\u003c/p\u003e\n\u003cp\u003eThe chemical oxygen demand represents the amount of oxygen consumed by oxidizable materials in the water. The decrease in COD in the presence of the ZnO catalyst is explained by the absorption of light by the catalyst and the production of hydroxyl radicals responsible for the degradation of organic matter.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1.6 Nitrites\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of nitrites during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.8.\u003c/p\u003e\n\u003cp\u003eFor the ZnO concentration of 0.5 g/L; the nitrite concentration increases from 0.0086 up to 0.0162 mg/L after 4h of treatment and then decreases to 0.0130 mg/L at t=5h.\u003c/p\u003e\n\u003cp\u003eFor the concentration of 1 g/L of ZnO; the nitrite concentration increases from 0.0086 to 0.0125 mg/L after 3h of treatment and then decreases to 0.0113 mg/L at t=5h.\u003c/p\u003e\n\u003cp\u003eFor 1.5 g/L ZnO concentration; nitrite concentration increases during treatment from 0.0086 up to 0.0195 mg/L.\u003c/p\u003e\n\u003cp\u003eNitrites can affect the photo catalytic process in several ways :\u003c/p\u003e\n\u003cp\u003e- Radical and hole scavengers which influence the quantum efficiency and thus the oxidation efficiency of the pollutant,\u003c/p\u003e\n\u003cp\u003e- Compete with the drug during adsorption to ZnO.\u003c/p\u003e\n\u003cp\u003e- Capture photons. - Corrosion or alteration of the photocatalyst.\u003c/p\u003e\n\u003cp\u003e- React directly with the photo catalyst (Chong, 2010) :\u003c/p\u003e\n\u003cp\u003eHowever, it is interesting to recall that the relative effects of these ions on the photo catalytic process can be variable depending on the pH which influences the zwitterionic nature of ZnO.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.1.7 Concentration of diclofenac\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation in concentration during heterogeneous photo catalytic treatment as a function of the three ZnO concentrations is shown in Figure.9.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the three studied ZnO concentrations (0.5; 1 and 1.5 g/L), the diclofenac concentration decreases to (50.06; 58.65 and 48.11 mg/L) respectively.\u003c/p\u003e\n\u003cp\u003eThe performance of the heterogeneous photo-catalytic degradation of diclofenac as a function of the three ZnO concentrations is shown in Figure.10.\u003c/p\u003e\n\u003cp\u003eThe concentration of 1.5 g/L of ZnO gives a high percentage removal in diclofenac concentration which is 52%.\u003c/p\u003e\n\u003cp\u003eThe presence of more ZnO can lead to the formation of zinc oxide aggregates which finally do not develop a larger ZnO-diclofenac contact surface than in the case of the 1g/L concentration, thus decreasing the percentage of degradation.\u003c/p\u003e\n\u003cp\u003eIncreasing the ZnO concentration to 1.5 g/L also leads to the formation of zinc oxide aggregates, but the catalytic surface area increases, leading to an increase in the percentage of degradation.\u003c/p\u003e\n\u003cp\u003eThe decrease in efficiency of one ZnO concentration compared to another can be explained by many characteristics.\u003c/p\u003e\n\u003cp\u003eHowever, characteristics such as specific surface area, charge recombination, interfacial charge transfer dynamics, particle size, crystallinity, pH etc. can have an influence.\u003c/p\u003e\n\u003cp\u003eOn the other hand, the activity of a photocatalyst is also influenced by the type of degradation intermediates generated. A study carried out by (Ryu and Choi 2007) has shown that the photo catalytic activity varies according to the pollutant tested.\u003c/p\u003e\n\u003cp\u003eIndeed, by applying a high concentration of ZnO, more photons can be absorbed and therefore more radicals can be formed. In addition, more diclofenac can be adsorbed on the surface of the photo-catalyst. This promotes the degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2 Influence of diclofenac concentration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study of heterogeneous photo catalytic degradation was carried out with three concentrations of diclofenac (50; 75 and 100 mg/L). The concentration of the ZnO catalyst is 1.5 g/L. The volume flow rate is 20.5 mL/s.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2.1 Hydrogen potential (pH)\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe pH variation during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.11.\u003c/p\u003e\n\u003cp\u003eThe pH increases from (7.38; 7.26 and 7.22) to (8.37; 8.45 and 7.89) respectively for the three concentrations studied and after 1 hour of treatment and then decreases until the end of treatment. These results can be explained by the competition reactions for the active sites on the surface of ZnO which involves the displacement of OH- ions, thus decreasing the trapping of holes by these hydroxyl ions and reducing the charge separation.\u003c/p\u003e\n\u003cp\u003eMoreover, the occupation of these active sites can lead to the exclusion of organic compounds from the active sites on the surface of the photo-catalyst (Burns 1999). .\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2.2 Electrical conductivity (EC)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe EC variation during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.12.\u003c/p\u003e\n\u003cp\u003eFor both concentrations (50 and 100 mg/L) of diclofenac; conductivity increases from (22.6 and 28.9 \u0026micro;S/cm) to (99 and 77.8 \u0026micro;S/cm) respectively during treatment.\u003c/p\u003e\n\u003cp\u003eFor the concentration of 75 mg/L diclofenac; conductivity increases from 24 to 91.4 \u0026micro;S/cm after 1h of treatment and then decreases to 34.5 \u0026micro;S/cm at t=2h and remains constant.\u003c/p\u003e\n\u003cp\u003eThe EC of the aqueous solution is mainly related to the presence of ions in the medium. The results show that the EC value obviously takes a significant part in the degradation of the organic compound. Indeed, the higher the conductivity, the greater the degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2.3 Turbidity (Tu)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Tu during the heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.13.\u003c/p\u003e\n\u003cp\u003eFor the concentration of 50 mg/L diclofenac; turbidity increases from 4.6 up to 32 NTU after 2h above t=2h the Tu is unstable (values are between 13.2 and 18 NTU).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the concentration of 75 mg/L of diclofenac; turbidity increases from 4.1 to 19.8 NTU after 1 hour of treatment and then it varies little (between 8.6 and 10.7 NTU).\u003c/p\u003e\n\u003cp\u003eFor 100 mg/L diclofenac concentration; turbidity increases from 2.9 to 15.7 NTU at t=5h.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe variation in turbidity during treatment may be due to light-deflecting degradation products. Thus, photo-dismutation of the catalyst may be possible.\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2.4 Surface tension (Ts)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Ts during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.14.\u003c/p\u003e\n\u003cp\u003eFor the concentrations studied (50; 75 and 100 mg/L) of diclofenac; fluctuations are observed during treatment.\u003c/p\u003e\n\u003cp\u003eThe observed fluctuations in surface tension are explained by the fact that during treatment, the diclofenac molecule is degraded leading to degradation by-products that compete with the parent molecule. This calls for a concentration gradient in the liquid which influences the Solid/Liquid contact surface.\u003c/p\u003e\n\u003cp\u003eOne can distinguish the angle at the advance \u0026theta;a which is at the front of the drop or liquid front and the angle at the retreat \u0026theta;r which is at the back\u0026nbsp; and generally, \u0026theta;a\u0026gt;\u0026theta;e\u0026gt;\u0026theta;r (De Gennes 1985, Dussan 1976).\u003c/p\u003e\n\u003cp\u003eThe difference between these different angles comes in particular from the roughness and heterogeneity (chemical, morphological ...) of the surface, or the degradation by-products.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2.5 Chemical oxygen demand (COD)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation in COD during heterogeneous photo catalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.15.\u003c/p\u003e\n\u003cp\u003eFor all three concentrations (50; 75 and 100 mg/L) of diclofenac; COD decreases from (130; 250 and 360 mg O2/L) to (32; 90 and 116 mg O2/L) respectively.\u003c/p\u003e\n\u003cp\u003eChemical Oxygen Demand (COD) represents the amount of oxygen consumed by oxidizable materials in the water.\u003c/p\u003e\n\u003cp\u003eThe decrease in COD in the presence of the ZnO catalyst is explained by the absorption of light by the catalyst and the production of the hydroxyl radicals responsible for degradation.\u003c/p\u003e\n\u003cp\u003eDegradation products can also induce different interactions between ZnO and diclofenac, especially in the case of negatively charged compounds at basic pH such as carboxylic acids, which appear in the mechanisms of photo-catalytic degradation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDifferent diclofenac/ZnO surface interactions could lead to a modified degradation mechanism and thus to different kinetics.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2.6 Nitrites \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of nitrites during heterogeneous photocatalytic treatment as a function of the three concentrations of diclofenac is shown in Figure.16.\u003c/p\u003e\n\u003cp\u003eFor all three concentrations (50; 75 and 100 mg/L) of diclofenac; the nitrite concentration increases during treatment from (0.0086; 0.0087 and 0.0086 mg/L) to (0.0188; 0.0224 and 0.0195 mg/L) respectively.\u003c/p\u003e\n\u003cp\u003eThe increase in nitrite concentration indicates that degradation begins with the breakdown of the nitrogen bond and the cyclic nucleus of diclofenac.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.2.7 Concentration of diclofenac\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation in concentration during heterogeneous photo catalytic treatment is shown in Figure.17.\u003c/p\u003e\n\u003cp\u003eFor all three concentrations (50; 75 and 100 mg/L) the concentration of diclofenac decreases during treatment to (29.15; 42.47 and 48.11 mg/L) respectively.\u003c/p\u003e\n\u003cp\u003eThe yield of heterogeneous photo-catalytic degradation to diclofenac is shown in Figure.18.\u003c/p\u003e\n\u003cp\u003eThe 100 mg/L concentration of diclofenac gives a high percentage of elimination which is 52%.\u003c/p\u003e\n\u003cp\u003eThe higher the initial concentration of diclofenac, the greater the efficiency of the photo-catalytic degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.3 Influence of the hydrogen peroxide (H2O2) concentration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study of heterogeneous photo catalytic degradation was carried out using hydrogen peroxide H2O2 whose ratio r = [H2O2]/[ZnO] is (1 ; 5 and 10%).\u003c/p\u003e\n\u003cp\u003eThe concentration of diclofenac is 100 mg/L. The catalyst concentration is 1.5 g/L. The volume flow rate is 20.5 mL/s.\u003c/p\u003e\n\u003cp\u003eThe results showed that degradation is complete after 1h of treatment for all three r-ratios. These results are confirmed by the absence of the diclofenac absorption peak (274 nm). The absorption spectrum of diclofenac is shown in Figure.19.\u003c/p\u003e\n\u003cp\u003eThese results are explained by the effect of hydrogen peroxide on the optical properties of ZnO. A study (Ozgur. U et al., 2005) has shown that in the presence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, ZnO has an emission band with a maximum of 3.24 eV and a wide composite band composed of three sub-bands at 2.2 eV; 2.06 eV and 1.8 eV. This promotes the formation of a large amount of OH.\u003c/p\u003e\n\u003cp\u003eThus, the concentration of hydrogen peroxide causes an increase in the amount of OH. radicals in the medium and therefore the degradation yield increases.\u003c/p\u003e\n\u003cp\u003eIt should also be noted that the quantity of the organic pollutant drops abruptly after one hour of treatment. This high efficiency is mainly due to the rapid formation, in large quantities, of OH radicals. which facilitates the attack between a large quantity of the oxidizing agent and diclofenac.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.3.1 Hydrogen potential (pH)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of pH during heterogeneous photo catalytic treatment as a function of the three ratios r is shown in Figure.20.\u003c/p\u003e\n\u003cp\u003eFor the 1% ratio; the pH decreases from 7.22 to 6.14 after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eFor both ratios (5 and 10%); the pH increases from 7.22 to (8.23 and 7.41) respectively after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eFor pH values more acidic than PZC (Im 2012), the ZnO particle will be positively charged and attraction will be favoured for anionic molecules.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.3.2 Electrical conductivity (EC)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of EC during heterogeneous photo catalytic processing as a function of the three ratios r is shown in Figure.21.\u003c/p\u003e\n\u003cp\u003eFor all three ratios (1; 5 and 10%); EC increases from 28.9 to (43.6; 38.1 and 34.7 \u0026micro;S/cm) respectively after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eThe EC of the aqueous solution is mainly related to the presence of ions in the medium. The results show that the EC value obviously takes a significant part in the degradation of the organic compound. The increase in electrical conductivity is due to the presence of the degradation compounds of diclofenac. Indeed, the higher the conductivity, the greater the degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.3.3 Turbidity (Tu)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Tu during photo-catalytic treatment as a function of the three ratios r is shown in Figure 22.\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor all three ratios (1%; 5% and 10%); Tu increases from 2.9 to (9.6; 7.4 and 8.3 NTU) respectively after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eTurbidity is an important parameter and is likely to affect the photocatalytic efficiency. Indeed, high turbidity can affect the optical properties and hinder light penetration. This will decrease the absorption of photons by the photocatalyst.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.3.4 Surface tension (Ts)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Ts during heterogeneous photo-catalytic treatment as a function of the three ratios r is shown in Figure.23.\u003c/p\u003e\n\u003cp\u003eFor all three ratios (1; 5 and 10%); Ts increases from 56.9 to (58.81; 61.35 and 69.74 mN/m) respectively after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eAs the surface tension increases, the catalyst is well wetted, which may increase the transfer of liquid/solid material. This increases the photocatalytic efficiency.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.3.5 Nitrites\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of nitrites during heterogeneous photocatalytic treatment as a function of the three ratios r is shown in Figure.24.\u003c/p\u003e\n\u003cp\u003eFor all three ratios (1; 5 and 10%); nitrite increases from 0.0086 to (0.0227; 0.0097 and 0.0267 mg/L) respectively after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eThe increase in nitrite concentration indicates that degradation begins with the breakdown of the nitrogen bond and the cyclic nucleus of diclofenac.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4 Influence of volume flow rate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study of heterogeneous photo catalytic degradation was performed at three volume flow rates (20.5; 22 and 25 mL/s). The concentration of diclofenac is 100 mg/L. The catalyst concentration is 1.5 g/L.\u003c/p\u003e\n\u003cp\u003eThe results showed that the degradation is complete for the volume flow rate 25 mL/s after 1h of treatment.\u003c/p\u003e\n\u003cp\u003eThis result is confirmed by the absence of the diclofenac absorption peak (274 nm).\u003c/p\u003e\n\u003cp\u003eThe absorption spectrum of diclofenac for the 25 mL/s volume flow rate is shown in Figure.25.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4.1 Hydrogen potential (pH)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of pH during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.26.\u003c/p\u003e\n\u003cp\u003eFor both volume flows (20.5 and 22 mL/s); the pH increases from 7.22 to (7.89 and 8.73) respectively at t=1h and then varies little.\u003c/p\u003e\n\u003cp\u003eFor the volume flow rate of 25 mL/s, the pH increases from 7.22 to 8.25 after 1h of treatment.\u003c/p\u003e\n\u003cp\u003eThe increase in pH is due to competition reactions for the active sites on the surface, which involves the displacement of OH- ions, thus reducing the trapping of holes by these hydroxyl ions and reducing charge separation.\u003c/p\u003e\n\u003cp\u003eMoreover, the occupation of these active sites can lead to the exclusion of organic compounds from the active sites on the surface of the photo-catalyst [18].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4.2 Electrical conductivity (EC)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of EC during heterogeneous photocatalytic treatment as a function of the three volume flows is shown in Figure 27.\u003c/p\u003e\n\u003cp\u003eFor the volume flow rate of 20.5 mL/s; the EC increases from 28.9 to 74.5 \u0026micro;S/cm after 3 hours of treatment; beyond 1 hour the EC varies little.\u003c/p\u003e\n\u003cp\u003eFor a volume flow rate of 22 mL/s; EC increases from 28.9 to 51.6 \u0026micro;S/cm after 1h of treatment, then decreases to 38.2 at t=2h, after 2h it varies little.\u003c/p\u003e\n\u003cp\u003eFor a volume flow rate of 25 mL/s; EC increases from 28.9 to 40.1 \u0026micro;S/cm after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eThe electrical conductivity of the aqueous solution is mainly related to the presence of ions in the medium. The results show that the EC value obviously takes a significant part in the degradation of the organic compound. Indeed, the higher the conductivity, the greater the degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4.3 Turbidity (Tu)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Tu during the heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.28.\u003c/p\u003e\n\u003cp\u003eFor volume flow rate of 20.5 mL/s; Tu increases from 2.9 to 15.7 NTU at t=5h.\u003c/p\u003e\n\u003cp\u003eFor volume flow rate of 22 mL/s; Tu increases from 2.9 to 37 NTU at t=5h.\u003c/p\u003e\n\u003cp\u003eFor volume flow rate of 25 mL/s; Tu increases by 2.9 NTU to 33.1 NTU after 1h of treatment.\u003c/p\u003e\n\u003cp\u003eHigh turbidity can affect the optical properties and hinder light penetration. This will decrease the absorption of photons by the photocatalyst.\u003c/p\u003e\n\u003cp\u003eSome authors have shown that a turbidity lower than 5 NTU would not affect light penetration.\u003c/p\u003e\n\u003cp\u003eAbove this value, turbidity would interfere with optimal use of light (Fernandez-Ibanez 2009, Gelover 2006, Chong 2010).\u003c/p\u003e\n\u003cp\u003eThis explains the decrease in the efficiency of photo catalytic treatment when turbidity increases.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4.4 Surface tension (Ts)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of Ts during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.29.\u003c/p\u003e\n\u003cp\u003eFor a volume flow rate of 20.5 mL/s; Ts varies little (between 56.9 and 59.76 mN/m).\u003c/p\u003e\n\u003cp\u003eFor a volume flow rate of 22 mL/s; Ts decreases from 56.9 mN/m to 40.97 mN/m at t=4h and then increases to 64.96 mN/m at t=5h.\u003c/p\u003e\n\u003cp\u003eFor the volume flow rate of 25 mL/s; Ts increases from 56.9 to 62.31 mN/m after 1h of treatment.\u003c/p\u003e\n\u003cp\u003eThe surface tension of the solutions is lower than that of pure water (72 mN/m). The interaction between the phases in a reactor depends on the velocity and physico-chemical properties of the fluid phases, as well as the geometric and physico-chemical properties of the solid particles. It is important to note that the contact surface between phases, which itself depends on the surface tension, varies according to the flow regime.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4.5 Chemical Oxygen Demand (COD)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of COD during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.30.\u003c/p\u003e\n\u003cp\u003eFor both volume flow rates (20.5; 22 mL/s); COD decreases from 360 to (116 and 15 mg O2/L) respectively during treatment.\u003c/p\u003e\n\u003cp\u003eFor the 25 mL/s volume flow rate, COD decreases from 360 to 15 mg O2/L after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eChemical Oxygen Demand (COD) represents the amount of oxygen consumed by oxidizable materials in the water. The decrease in COD in the presence of the ZnO catalyst is explained by the absorption of light by the catalyst and the production of hydroxyl radicals responsible for degradation. It can be seen that the rate of mineralization is rapid at the beginning of the treatment and then it decreases. Indeed, at the beginning of the treatment, the mother molecule and its degradation products are more easily oxidized by hydroxyl radicals leading to the formation of aliphatic compounds like carboxylic acids... (Oturan, 2000, Brillas 2003, Boye 2002, Diagne, 2007) that resist well to mineralization by these same radicals.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4.6 Nitrites \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation of nitrites during heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.31.\u003c/p\u003e\n\u003cp\u003eFor both volume flow rates (20.5; 22 mL/s); the nitrites increase from 0.0086 to (0.0195; 0.0178 mg/L) respectively after 5h of treatment.\u003c/p\u003e\n\u003cp\u003eFor the volume flow rate 25 mL/s, nitrite increases from 0.0086 to 0.0109 mg/L at t=1h.\u003c/p\u003e\n\u003cp\u003eThe increase in nitrite concentration indicates that degradation begins with the breakdown of the nitrogen bond and the cyclic nucleus of diclofenac.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNitrites can affect the photocatalytic process in several ways:\u003c/p\u003e\n\u003cp\u003e- Radical and hole traps which influence the quantum efficiency and thus the oxidation efficiency of the pollutant,\u003c/p\u003e\n\u003cp\u003e- Compete with the drug during adsorption to ZnO,\u003c/p\u003e\n\u003cp\u003e- Capturing photons - Corrosion or alteration of the photocatalyst\u003c/p\u003e\n\u003cp\u003e- React directly with the photo catalyst (Chong 2010).\u003c/p\u003e\n\u003cp\u003eHowever, it is interesting to recall that the relative effects of these ions on the photo catalytic process can be variable as a function of the pH, which influences the zwitterionic nature of ZnO.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII.4.7 Concentration of diclofenac\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe variation in concentration during the heterogeneous photo catalytic treatment as a function of the three volume flows is shown in Figure.32.\u003c/p\u003e\n\u003cp\u003eFor both volume flow rates (20.5; 22 mL/s) the diclofenac concentration decreases to (48.11; 24.56 mg/L) respectively during treatment.\u003c/p\u003e\n\u003cp\u003eFor the volume flow rate 25 mL/s, the diclofenac concentration decreases from 100 to 12.35 mg/L after 1 hour of treatment.\u003c/p\u003e\n\u003cp\u003eThe photo-catalytic degradation performance of diclofenac as a function of the three flow rates is shown in Figure.33.\u003c/p\u003e\n\u003cp\u003eThe volume flow rate of 25 mL/s gives the highest removal percentage (100%).\u003c/p\u003e\n\u003cp\u003eThe increase in degradation yield with increasing flow rate is explained by :\u003c/p\u003e\n\u003cp\u003eThe thickness of the absorbent layer of the treated fluid varies along the reactor. Indeed, at the reactor inlet, the conversion is null x = 0, and the absorbent layer consists only of ZnO. In this case, the majority of the photons are absorbed by the ZnO.\u003c/p\u003e\n\u003cp\u003eThen along the reactor, the conversion progresses and the layer becomes depleted in diclofenac and, conversely, it becomes enriched in degradation compounds. The photons are then absorbed by both ZnO and degradation compounds.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe distribution of the absorbed photons between ZnO and the degradation compounds will depend on the hydrodynamic conditions of the reactor.\u003c/p\u003e\n\u003cp\u003eThe hydrodynamic regime is defined by the Reynolds number.\u003c/p\u003e\n\u003cp\u003eTable 1 regroups the Reynolds number for the three volume flows studied.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e The Reynolds number for the different volume flows.\u003c/p\u003e\n\u003ctable border=\"1\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026rho; (Kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e10\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026micro; (Pa.s)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e10\u003csup\u003e-3 \u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;V (mL/s)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e20.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e22\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e25\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e\n\u003cp\u003e\u003cstrong\u003eRe\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e2611\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e2802\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd\u003e\n\u003cp\u003e3184\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFor both volume flows (20.5 and 22 mL/s) the regime is transient.\u003c/p\u003e\n\u003cp\u003eFor the volume flow rate of 25 mL/s the regime is turbulent.\u003c/p\u003e\n\u003cp\u003eFor a given Reynolds number, the efficiency of photo-catalysis is influenced by :\u003c/p\u003e\n\u003cp\u003e- The amount of material passing through the reactor.\u003c/p\u003e\n\u003cp\u003e- The residence time 𝜏𝑠 of the molecules in the reactor.\u003c/p\u003e\n\u003cp\u003e- The light power.\u003c/p\u003e\n\u003cp\u003eThe flux density of incident photons will play on the local speed of the photochemical reaction, which can impact the local and average characteristic times in the zone of illuminated fluid.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis work focused on the study of the elimination of a non-steroidal anti-inflammatory drug (diclofenac) using heterogeneous photo catalysis as a treatment.\u003c/p\u003e\n\u003cp\u003eThe study investigated the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r=[H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e]/[ZnO] and volume flow) on the photocatalytic degradation of diclofenac.\u003c/p\u003e\n\u003cp\u003eThe analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration.\u003c/p\u003e\n\u003cp\u003eThe heterogeneous photo catalytic degradation is influenced by :\u003c/p\u003e\n\u003cp\u003e-The concentration of the ZnO catalyst.\u003c/p\u003e\n\u003cp\u003eThe concentration of 1.5 g/L gives a better degradation in diclofenac with a 52% removal percentage.\u003c/p\u003e\n\u003cp\u003e-The initial concentration of diclofenac.\u003c/p\u003e\n\u003cp\u003eThe concentration of 100 mg/L of diclofenac gives a better degradation with a percentage of elimination of 52%.\u003c/p\u003e\n\u003cp\u003e-The ratio r =([H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e])/([ZnO]).\u003c/p\u003e\n\u003cp\u003eThe three ratios (1; 5 and 10%) give a total degradation after one hour of treatment.\u003c/p\u003e\n\u003cp\u003e-The volume flow rate.\u003c/p\u003e\n\u003cp\u003eThe volume flow rate of 25 mL/s gives a total degradation after one hour of treatment.\u003c/p\u003e\n\u003cp\u003eOptimal conditions for heterogeneous photo-catalysis are :\u003c/p\u003e\n\u003cp\u003e[ZnO] = 1.5 g/L, [diclofenac] = 100 mg/L, volume flow rate = 25 mL/s.\u003c/p\u003e\n\u003cp\u003eFor a volume flow rate of 20 mL/s, optimal conditions are achieved by adding H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eEthics approval and consent to participate \u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eThe results and materials presented in this article are realized in the laboratory of \u003cem\u003eLaboratory of Electrochemistry-Corrosion, Metallurgy and Inorganic Chemistry. Faculty of Chemistry. University of Sciences and Technology. Houari Boumediene. Box N\u0026deg;32 El-Alia. Bab-Ezzouar. Algiers. Algeria. \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe data tables are presented in different forms in the manuscript and are available from the authors.\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eThe authors Fateh Naitali and Hafida Ghoualem declare that they have no competing interests\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eFunding \u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eThe authors Fateh Naitali and Hafida Ghoualem received no specific funding for this work\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eAuthors' contributions\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eAuthor Fateh Naitali was a major contributor in working and writing the manuscript.\u003c/p\u003e\n\u003cp\u003eAuthor Hafida Ghoualem was a major contributor in working and writing the manuscript.\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors Fateh Naitali and Hafida Ghoualem declare that they have no competing financial interests\u003c/p\u003e\n\u003cp\u003eThere are no competing interests related to this work\u003c/p\u003e\n\u003cp\u003eThere are no known conflicts of interest associated with this publication\u003c/p\u003e"},{"header":"References","content":"\u003cp\u003e\u003cstrong\u003eBoye\u003c/strong\u003e B, Dieng M. 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Environ Sci Techol 37 1061- 1068.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTurchi\u003c/strong\u003e C.S, Ollis D.F (1990) Photocatalytic degradation of organic water contaminants: mechanisms involving hydroxyl radical attack. J. Catal 122 .178-192.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eValizadeh\u003c/strong\u003e H, Azimi A.A (2011) ZnO/MgO containing ZnO nanoparticles as a highly effective heterogeneous base catalyst for the synthesis of 4\u003cem\u003eH\u003c/em\u003e-pyrans and coumarins in [bmim]BF\u003csub\u003e4\u003c/sub\u003e\u0026nbsp;.\u0026nbsp;\u003cem\u003eJICS\u003c/em\u003e\u0026nbsp;8,\u0026nbsp;123\u0026ndash;130.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"USTHB","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Photo degradation, drugs, double-tube reactor, volume flow, ZnO, H2O2","lastPublishedDoi":"10.21203/rs.3.rs-162545/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-162545/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis work focused on the study of the elimination of a non-steroidal anti-inflammatory drug (diclofenac) using heterogeneous photo catalysis as a treatment.\u003c/p\u003e\u003cp\u003eThe study investigated the effect of parameters (catalyst concentration, initial diclofenac concentration, ratio r r = . and volume flow) on the photocatalytic degradation of diclofenac. The analyses performed are pH, electrical conductivity, turbidity, surface tension, chemical oxygen demand, nitrite and diclofenac concentration.\u003c/p\u003e\u003cp\u003eThe study showed that: The heterogeneous photo catalytic degradation is influenced by :\u003c/p\u003e\u003cp\u003eThe concentration of the ZnO catalyst; The concentration of 1.5 g/L gives a better degradation in diclofenac with a percentage of elimination of 52%; The initial concentration of diclofenac; The concentration of 100 mg/L of diclofenac gives a better degradation with a percentage of elimination of 52%; The ratio r = ; The three ratios (1; 5; and 10%) give a total degradation after one hour of treatment; The volume flow rate of 25 mL/s gives a total degradation after one hour of treatment. Optimal conditions for heterogeneous photo-catalysis are : [ZnO] = 1.5 g/L, [diclofenac] = 100 mg/L, Volume flow rate = 25 mL/s \u003c/p\u003e\u003cp\u003eFor a volume flow rate of 20 mL/s, optimal conditions are met by adding H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u0026nbsp;\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","manuscriptTitle":"Photocatalytic decontamination of pharmaceutical effluent in a double tube reactor by ZnO catalyst. Physico chemical characterization and optimization.\u0026nbsp;","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-01-29 17:13:25","doi":"10.21203/rs.3.rs-162545/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1a8ac828-1a84-471d-a935-d9b50200a63e","owner":[],"postedDate":"January 29th, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":2131459,"name":"Environmental Engineering"}],"tags":[],"updatedAt":"2021-01-29T17:13:25+00:00","versionOfRecord":[],"versionCreatedAt":"2021-01-29 17:13:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-162545","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-162545","identity":"rs-162545","version":["v1"]},"buildId":"FbvkV6FR0MCFSLy54lSbu","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}