Advanced Oxidation of Antibiotics Polluted Water Using Titanium Dioxide in Solar Photocatalysis Reactor

The aim of this study was to investigate antibiotic amoxicillin removal from synthetic pharmaceutical wastewater. Titanium dioxide (TiO2) was used in photocatalysis treatment method under natural solar irradiation in a tubular reactor. The photocatalytic removal efficiency was evaluated by the reduction in amoxicillin concentration. The effects of antibiotics concentration, TiO2 dose, irradiation time and the effect of pH were studied. The optimum conditions were found to be irradiation time 5 hr, catalyst dosage 0.6 g/L, flow rate 1 L/min and pH 5. The photocatalytic treatment was able to destruct the amoxicillin in 5 hr and induced an amoxicillin reduction of about 10% with 141.8 kJ/L accumulated solar energy per liter of solution.


INTRODUCTION
Through the last decades, antibiotics have been widely utilized for disease treatment )Heberer, et al., 1997(. Previous studies had discovered pharmaceutical substances existence in the normal ecosystems, which resulted in contamination to the origins of drinking water, surface water, and groundwater, (Putschew et al., 2000;Sacher et al., 2001;and Anderson et al., 2004). The origins of such substances always arrive from the expelling of human's waste, where the managed as pharmaceutical substances cross through the human body unchanged, i.e., as parent substance or metabolite, into feces and urine, (Ternes, 1996). Three of them are quite often discovered in the aqueous surrounding are carbamazepine (CBZ), amoxicillin (AMX) and diclofenac (DCF), . Amoxicillin (AMX) Fig. 1 is an antibiotic that belongs to penicillin's group. The amoxicillin chemical structure composed of "d-4-hydroxyphenylglycine" side chain linked to 6-aminopenicillanic acid (6-APA) moiety. From the other side, Amoxicillin is a wide spectrum antibiotic utilized for treating the infections of bacterial resulted via sensitive microorganisms, (Chatterjee et al., 2014). This drug includes capsules, tablets, powder, and injections as well as in combination with other ingredients. Because of antibiotics less bio-degradability, they're partially eliminated in the traditional wastewater processing plants, by that means, giving a great contamination danger into the bodies that receive water, (   There are several technologies for amoxicillin elimination as well as filtration, biological processes, coagulation, flocculation, sedimentation, (Homem and Santos, 2011) ozonation, ion-exchange, membrane and adsorption, (Chatterjee et al., 2014). The sustainable and influential processing of pharmaceutical factory and hospital wastewater that contains a high level of these substances introducing an essential challenge to the engineers of wastewater and environment all over the world. "Advanced oxidation processes", AOPs, have introduced more capability for contaminants elimination from the wastewater. The contaminants elimination from wastewater via AOPs depends upon the procreation of hydroxyl radicals, which have the ability to oxidize the inorganic and organic intricate substances, ( Murgolo et al., 2014). Catalyst being a semi-conductor that absorbs the apparent light (320-750 nm) desired photons transformed energy into the carriers of charge, (Alrousan et al., 2012). Accordingly, the reactors of solar photo-catalytic have taken a significant concern. The reactor design is greatly significant to secure the effective change of incidental solar radiation to the carriers of charge, (Bahnemann et al., 1991). Various reactor shapes were utilized for degrading different kinds of pollutants employing the solar light or the artificial light that simulates the sunlight. The four often utilized reactor shapes are parabolic double-skin sheet reactor, DSSR; compound parabolic collector, CPC; thin-film fixed bed reactor, TFFBR; and parabolic trough reactor, PTR, (Bahnemann et al., 1991 andGoswami, 1997). Tubular reactors are a variation of other reactors types like (CPC); the discrepancy is the reflector absence that permits (CPC) to possess a small factor of concentration. However, the tubular reactors are subjected to the optical losses owing to the absorbance of (UV) via the tube and the material of reflector. The additional feature is the aging of glass tubes, which is recognized as "UV-solarization". The more prolonged solar radiation exposure causes additional decrease of the tubes (UV) transmittance that impairs the efficiency of processing and incurs further costs for the regular substitution of tubes. The objective of the present study is to evaluate the antibiotic amoxicillin elimination from synthetic wastewater using a tubular photoreactor model under the natural solar irradiation and assess the possibility of such technique for water reclamation.

MATERIAL AND PROCEDURES 2.1. Chemicals
Amoxicillin AMX (C16H19N3C5S) with a molecular weight of 365.4 g/mol was taken from Samarra Pharmaceutical State Company. Sodium hydroxide NaOH, Sulfuric acid H2SO4 (these chemicals were used to change the pH value) (Sigma-Aldrich) and Titanium dioxide TiO2 photocatalytic were provided by HIMEDIA Company (India), (purity more than 99.0%) with a molecular weight of 79.87 g/mol. flow (ranging from 1 to 6 L/min) that was supplied via a pump to provide a regulated circulating flow in the glass tubes. The pilot plant was fixed and tilted at an angle of 45°. The synthetic wastewater was prepared in a glass tank. For reaching the uniform states within this tank, a mechanical blender was utilized. The experimental diagram of the solar photocatalytic reactor system concept and the actual photo of the experimental setup are illustrated in Fig. 2 and Fig. 3, respectively.

Solar Experiments
The synthetic pharmaceutical wastewater (5, 7.5 and 10 mg/l of AMX) was mixed with a proper quantity of TiO2 (100 to 1000 mg/l) and then conveyed to the reactor that is exposed to natural sunlight. The processed water that comes out of this reactor is blended with the water in the tank of containment. This treatment proceeds until the blended concentration in the tank of containment attains a maximum removal. The whole experiments were carried out in the sunny days of July and August 2018. The states of climate (solar irradiance and surrounding temperature) were usual in such period of year at such site. The measurement of the (UVA) radiation was conducted at the "Center of Journal of Engineering Volume 26 February 2020 Number 2 5 Solar Energy Research -Ministry of Science and Technology" utilizing "Davis 6152 C Vantage Pro 2 Weather Station radiometer". This device supplies the information in terms of the incident (UVA-W/m 2 ); the mean solar irradiance for the whole experiments was (763 W/m 2 ) during the interval (8:30-1:30) local time, with a peak magnitude of (905 W/m 2 ) recorded during the period from 9:00 am to 1:00 pm. The water specimen's temperature and pH within the solar experiments were from (40 • C ± 1.6) to (43 • C ±3.8) by using thermometer (Hanna instruments, Spain) and pH meter (multi720, WTW, Germany). The initial specimen was collected, and the reactor was subjected to solar radiation. The specimens were gathered at consistent periods to obtain the change in concentrations. All experiments duration was 5 hours, starting at 8:30 am-1:30 pm local time. Specimens of 2.5 mL were first collected at consistent intervals of time, and the adequate amoxicillin concentration was then measured via the absorbance measurements that were performed on a Spectrophotometer UV-1800 (Shimadzu Corporation, Kyoto, Japan). The removal efficiency of AMX was calculated according to the following equation: Removal efficiency = (Cin -Cout /Cin)* 100% (1) Where Cin: inlet sample concentration (mg/liter), Cout: outlet sample concentration (mg/liter).
The quantity of energy gathered, per unit of volume, via the reactor from the test commence till every specimen composed may be obtained via Eq. 2 (Joa et al., 2014).
Where, and −1 : The (UV) energy gathered/liter (kJ/L) at the times n and n−1. : Mean incident radiation on the irradiated area ∆ : The testing time of specimen : The collector illuminated area (m 2 /m 3 ) and obtained via Equation (3) : The whole volume of treated water (L) where Ar : actual reactor area (m 2 ) t : irradiance time (h) Es : average solar irradiance (W/m 2 ) Vt :treated volume (L) Ci and Cf : initial and final concentrations (mg/L)  (100,200,300,400,500,600,700,800,900  The variation of solar intensity with time of illumination is plotted in Fig. 4. It can be noted from this figure that the maximum solar intensity was 900 W/m 2 at 12 pm in July 2018, where the maximum degradation of amoxicillin can be anticipated.  Fig. 6, the removal efficiency of amoxicillin after 5 hours indicates that with the TiO2 dose up to about 600 mg/L, the removal increases; however, above 600 mg/L, the removal of amoxicillin decreases after the same irradiation of sunlight times. This can be explained by that the solution raised turbidity decreases the light transfer within the solution which is relevant for TiO2 concentrations more than about 600 mg/L, whereas below such concentration of catalyst, it's assumed that the surface of catalyst and the light absorption via TiO2 particles are bounding (Javad and Fatemeh, 2012).

Effect of pH
The outputs of changing the pH values from 3 to 9 are shown in Fig. 7, and the amoxicillin peak elimination 7.8% were performed at pH 5. Since TiO2 has amphoteric behavior with a "zero point charge pH" of (6.25), (Saien et al., 2010), the formation of electron-hole, for adsorbing the anions, is preferred when the pH value is less than pHzpc. At lower pH (< 5), adsorption of the existed anions generated from the decomposition of supplemented sulfuric acid decreases the opportunity of amoxicillin adsorption within the surface of catalyst, and accordingly, the oxidation rate will be decreased, (Hoffmann et al., 1995). At pH more than (5), the catalyst surface will be negatively charged and repulse the antibiotics in water, and consequently reduce the removal efficiency, (Gomathi et al., 2010). Fig. 8 manifests the photocatalytic degrading efficiencies of amoxicillin at various rates of flow ranging from (1) to (6 L/min), it's obtained that the degradation efficiency of photocatalytic at flow rate (1 L/min) gives the highest removal about round (9.6%). If the rate of flow was (> 1 L/min), the efficiency of process would decrease since the pollutants residence time within the photocatalytic reactor reduced which possesses a passive influence on the rate of amoxicillin degradation.

Influence of initial concentration of amoxicillin
The influence of initial amoxicillin concentration on the elimination efficiency was studied via changing the concentrations of amoxicillin from (5 mg/L) to (10 mg/L) . Fig. 9 shows that increasing amoxicillin concentration will lead to a reduction in the elimination efficiency. The increase in amoxicillin removal at low concentrations of amoxicillin and also decrease in high concentrations may be clarified by changes in the reaction rate control mechanism. The reaction rate curb at smaller concentration when the active sites on the photocatalyst surface are partially occupied by adsorbed molecules changes to the mass transfer limitation at high AMX concentration; the active sites on TiO2 are occupied by amoxicillin molecules, then a new molecule cannot be adsorbed (Fatemeh and   Depending upon the all above-mentioned results; it is found that the optimum concentration of catalyst, solution flow rate and pH for the highest elimination are (600 mg/L), (1 L/min) and (5), respectively. Also, to evaluate the antibiotic removal due to adsorption of amoxicillin into surface of TiO2, an experiment was carried out with 10 mg/L of amoxicillin at pH = 5 in the absence of UV radiation. The reduction of AMX after 5 hours was (2%).

CONCLUSIONS AND RECOMMENDATIONS
The TiO2 was as a feasible solar photocatalyst for the removal of Amoxicillin, using a reactor to receive the solar irradiation. TiO2 concentration 600 mg/L with 5 pH and 1 L/min flow rate can be regarded as the optimum working circumstances. Through such circumstances the removal efficiency of AMX was greater than 9%. Amoxicillin degradation is positively influenced by solar energy because the amoxicillin oxidation is in direct proportionality to no. of the light photons that absorbed via the solution. The low efficiency can be explained by that the tubular reactor is a non-concentrating type, in which the water moves within the transparent pipes.