Photocatalytic Disinfection and Removal of Emerging Pollutants from

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Photocatalytic disinfection and removal of emerging pollutants from effluents of biological wastewater treatments using a newly developed large scale solar simulator Karine Philippe, Ruud Timmers, Rafael van Grieken, and Javier Marugan Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b04927 • Publication Date (Web): 03 Mar 2016 Downloaded from http://pubs.acs.org on March 12, 2016

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Industrial & Engineering Chemistry Research

Photocatalytic disinfection and removal of emerging pollutants from effluents of biological wastewater treatments using a newly developed large scale solar simulator Karine K. Philippe, Ruud Timmers, Rafael van Grieken, Javier Marugan* Department of Chemical and Environmental Technology, ESCET, Universidad Rey Juan Carlos, C/ Tulipán s/n, 28933, Móstoles, Spain. * [email protected]

KEYWORDS: disinfection, Escherichia coli, emerging pollutants, TiO2 photocatalysis, large scale solar simulator, biological effluents

ABSTRACT The reuse of sewage water treatment is becoming a priority especially in arid regions where water is scarce. However, there is raising concern about the presence of emerging micropollutants refractory to the conventional treatments in wastewater treatment plants. Solar TiO2 heterogeneous photocatalysis provides a valuable alternative for the simultaneous oxidation of chemical and inactivation of microorganisms. However, the variability of solar irradiance

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hinders the study of the process under controlled UV irradiance. This work reports the development of an innovative solar simulator and its validation against the use of natural sunlight in photocatalytic disinfection applications with simultaneous removal of emerging contaminants. The significant impact of osmotic and mechanical stress on the viability of E. coli bacteria was confirmed. UV irradiance and total-to-illuminated volume ratio showed no impact on the dependence of the bacteria inactivation kinetics on the energy accumulated in the system, indicating that the possible existence of dark repair mechanisms can be neglected within the studied irradiance range (20-60 W m-2). Average results show that after 3 kJ L-1 of accumulated energy, 5-logs of E. coli bacteria are inactivated whereas a removal efficiency above 80% is achieved for the micropollutants.

1. Introduction The growing world population and the climate change are some of the key issues leading to potable water scarcity. Spain is especially touched as it is the most arid country in the European Union and it devotes a significant amount of water to irrigation. Hence the reuse of sewage water treatment plant effluents could offer a solution to increase the water availability. However a special attention must be paid on the disinfection processes in order to fulfill the legislation requirements often using E. coli bacteria as a faecal contaminant indicator. Therefore water reuse is closely linked to disinfection processes. Conventional disinfection processes such as chlorination or ozonation are known to produce disinfection by-products (DBPs) with potential carcinogenic effects1,2. In addition, the occurrence of emerging contaminants (EC) in wastewater effluents is a growing concern since it unbalances our entire ecological systems. These EC are


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detected at trace concentration levels ranging from nanograms to micrograms per liter. They include pharmaceuticals, pesticides and hormones resulting from human activities such as farming, industries and hospitals. Previous studies have shown the inefficiency of conventional treatments to remove those pollutants3. Advanced oxidation processes (AOPs) provide a valuable alternative as they generate highly reactive radicals that have the potential to simultaneously oxidize chemical micropollutants and inactivate microorganisms which was reported by previous studies in our group4,5. Here we focused on the TiO2 heterogeneous photocatalysis which presents a number of advantages including non-toxicity, high stability, low cost of the TiO2 catalyst and mild operating conditions (natural pH, ambient temperature and pressure). The oxidation mechanism is based on the activation of a semiconductor material upon UV-A radiation, eventually producing radical species. Matsunaga et al.6 were the first to report death of microbial cells with a photoexcited powder. A number of studies have proved that TiO2 photocatalysis was a successful disinfection process7-11. Most of them focused on laboratory scale experiments and pilot-plant scale applications are scarce12. Here, the work was conducted in a large scale solar simulator based on a compound parabolic collector (CPC) which was built and optimized for this purpose. It was found to provide the best optics for low concentration systems and can be designed with a concentration ratio close to 1 and capturing both the direct and diffuse UV sunlight12. The use of renewable and free solar energy in such processes could substantially reduce treatment costs and be more environmental friendly. However, working under real sun conditions strongly limits the reproducibility, accuracy and tunability of operational variables required for experiments devoted to kinetic modelling, simulation and scaling up of photocatalytic reactors.


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The first part of the paper describes the construction and validation of a photocatalytic reactor based on a novel large scale solar simulator while the second part reports the efficiency of the simultaneous bacterial inactivation and micropollutant removal by slurry TiO2 photocatalysis in the CPC-based reactor. The effects of fluid dynamics regime, water composition, UV irradiance and total-to-illuminated volume ratio were assessed. 2. Large Scale Solar Simulator 2.1. CPC reactor The photoreactor consisted on four borosilicate 3.3 Duran® glass tubes (inner diameter of 26 mm) with a length of 380 mm placed in the focal line of CPC collectors. The system is mounted on a frame that allows variable tilt for real sun exposition and 90º when using the solar simulator (Figure 1). The aqueous suspension was recirculated through the reactor thanks to a centrifugal pump (NH-50PX-X, Pan World Co. Ltd) connected to a reservoir. The illuminated volume was 0.2 L per tube, whereas the total volume can be modified to work under different ratios of totalto-illuminated volume. Three different treated volumes were chosen 1, 1.5, and 2 L corresponding to a volume ratio (VR) of 5; 7.5 and 10 respectively. Relatively high values of volume ratio were chosen in order to eventually assess dark repair phenomena of the bacteria. If required, online temperature and pressure controllers allow the operation of refrigeration and flow regulation systems. 2.2. Solar simulator To mimic the solar spectrum a XBO® 5000W/H XL OFR Xenon short arc lamp with a color temperature of approximately 6000 K was used (Osram, Munich, Germany). The lamp was


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mounted on a cinema projector (Proyecson, Xenoluxe XL) using a customized reflector to meet the requirements of this specific application (details will be shown below). Figure 2 shows the photographs of the equipment. The UV irradiance and spectral distribution of the radiation was measured by a calibrated spectroradiometer (BlueWave StellarNet Inc.) and compared with the solar light in a sunny day at the location of the lab (40.331N, 3.88ºW). As shown in Figure 2, the emission of the lamp differs from the solar spectrum in the near infrared spectral range from 800 to 1000 nm and in the visible range wavelengths from 400 to 600 nm but reproduces quite reasonably the UV-A part of the solar spectrum responsible of the activation of TiO2 in photocatalytic processes. The main advantage of the use of this novel solar simulator is the possibility of working with CPC reactors under very precise, controllable and reproducible irradiation conditions. However, to ensure that the irradiation conditions are homogenous along the complete CPC surface area, the position of the lamp on the reflector axis must be finely tuned. Theoretical calculations based on the power and geometry of the lamp using a ray tracing software (TracePro, Lambda Research Corporation) allowed the optimization of the reflector system, showing the range of UV irradiances in which the system can operate using the full CPC surface without shadows. The simulations of the irradiation maps were successfully validated with experimental measurements (Figure 3) thanks to a black surface with a grid of 81 holes where a spectroradiometer probe was placed to measure the distribution of radiation. Optimal conditions were selected allowing to work at different levels of radiation ranging from 20 to 60 W m-2 of UV-A ensuring enough spatial uniformity with variations below 10%. Once the positions of the lamp and the CPC were fixed, UV irradiance can be adjusted using the potentiometer of the lamp power supply.


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The analysis and comparison of experimental results performed under different irradiation conditions, especially under real sunlight, can be facilitated using the accumulated energy in the system (QUV,n , kJ L-1) calculated as follows11: QUV,n = QUV,n-1 + ∆tn UVG,n ACPC / VTOT where tn is the experimental time for each sample, UVG,n is the average UVG during ∆tn, ACPC is the collector surface, VTOT is the total reaction volume. 2.3. TiO2 loading The optimal catalyst concentration for the operation of the reactor was theoretically estimated based on the radiation distribution inside the reactor. Optical properties from P25 TiO2 were taken from the literature13 and used for the estimation of the absorption and scattering of light by the TiO2 suspension. The boundary conditions of radiation inlet were fixed considering the CPC concentration factor of 1, meaning that the radiation flux on the tube surface was equal to the radiation flux reaching the reflection surface. Based on that assumption, the optimal distribution and average value of the local volumetric rate of photon absorption along the reactor volume was calculated, indicating an optimal TiO2 loading around 0.1 g L-1. This optimal value was experimentally validated in preliminary runs using the reaction rate of the photocatalytic oxidation of methanol to formaldehyde as test reaction14.

3. Experimental Methods 3.1. Water matrices


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Three different kinds of waters were used: (i) ultrapure, (ii) saline: ultrapure with addition of 0.9 wt% NaCl and (iii) a synthetic secondary wastewater treatment plant (SWTP) effluent15 diluted to a value of total organic carbon of 15 mg L-1. 3.2. Bacterial inactivation Escherichia coli K-12 strain was provided by the Colección Española de Cultivos Tipo (CECT4624, corresponding to ATCC 23631). E. coli was selected as model microorganism due to its wide use as faecal contamination indicator. A fresh liquid culture at a concentration of 109 colony forming units (CFU) per mL was prepared by inoculation in a Luria-Bertani agar nutrient medium (Miller’s LB Broth, Scharlab) and incubation for 18-24h at 37ºC under constant stirring in a rotary shaker incubator (ES20 Biosan). Subsequently the bacteria solution was diluted to 106 CFU mL-1. A standard serial dilution procedure and agar plating was performed using eight independent measurements for each sample thus obtaining statistically significant data. The Petri plates were then incubated for 24 hours at a temperature of 37°C before counting. No significant difference in the plate count was observed after 72 hours. The detection limit was 1 CFU mL-1. More details of the analytical procedure can be found elsewhere16. Each experiment was repeated three times to assess the reproducibility of the disinfection results, being estimated the average error interval of the calculated kinetic constants in ± 27%. 3.3. Micropollutants degradation As indicators for the removal of micropollutants, thirteen compounds purchased in Sigma Aldrich were chosen: nine pharmaceuticals corresponding to different families of drugs including 4-acetamidoantipyrine (AAA), atenolol (ATN); caffeine (CFN); carbamazepine (CZP); dicloflenac sodium salt (DCF); gemfibrozil (GFZ); hydrochlorothiazide (HCT); ibuprofen (IBP);


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ranitidine (RMT); one steroid hormone namely progesterone (PGT) and three pesticides including isoproturon (IPT); metamitron (MTM) and clofibric acid (ACF). The initial concentration of these pollutants was 20 µg L-1. Each sample was prefiltered before analysis using 0.22 µm regenerated cellulose syringe filters to remove catalyst and suspended matter. The quantification of micropollutants was carried out using a Varian 325 LC-MS/MS triple quadrupole mass spectrometer, equipped with a vortex electrospray ionization interface and a Pursuit XRs Ultra 2.8 C18 100 x 2.0 column. The quantification limit was around 10 ng L-1 5. The EC mix was spiked in the reactor at the same time as the bacteria so that the degradation was simultaneous.

4. Results and discussion 4.1. Influence of fluid dynamic regime and water composition The following section was carried out in dark conditions in absence of TiO2 hence the UV light was not considered. Here we looked at the influence of different fluid dynamics regimes on disinfection kinetics of E. coli. Three regimes were studied: laminar, transition and turbulent corresponding to a Reynolds number of 1400; 3000 and 8800 respectively in order to evaluate the effect of the mechanical stress on the bacteria degradation kinetics (Table 1). Additionally, the effect of the osmotic stress was evaluated using different types of waters: ultrapure water, saline water and SWTP effluent. In ultrapure water, (Figure 4a) results showed that bacteria were degraded by 3 log in turbulent regime as a result of osmotic stress and mechanical stress (k = 0.234 s-1). As expected, the degradation was slower in the case of laminar and transition regimes as the mechanical stress was proportionally lower with kinetics constants k of 0.062 and 0.150 s-1


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respectively. Similarly, Sichel et al.17 reported the strong impact of mechanical stress in CPC reactors on the viability of E. coli cells. Besides, previous reports4,18,19 highlighted the importance of osmotic stress on bacteria inactivation. They reported that the lack of ions lead to the leakage of calcium and magnesium ions from the cell wall and consequently the loss of bacterial permeability. This demonstrated that disinfection by photocatalysis was very sensitive to water composition. The temperature remained constant along the experiment so we considered the thermal effect negligible. A similar experiment was performed in saline water where the osmotic effect was negligible. Results were comparable and showed that the mechanical stress was significant especially in the case of the turbulent regime (Figure 4b). However, similar experiments were performed in SWTP and showed negligible degradation of bacteria where 0.5% of E. coli were removed (Figure 4c). This means that these conditions are suitable for modeling the disinfection of E. coli ensuring the control of the photocatalytic process over the global inactivation. The turbulent flow was used for all subsequent experiments to ensure a good mixing and aeration in the slurry reactor.

4.2. Influence of UV irradiance and total-to-illuminated volume ratio The inactivation of E. coli was assessed at different irradiances values 20; 40 and 60 W m-2 and fixed volume ratio of 7.5 versus accumulated energy (Figure 5a). Results showed that despite of the obvious increment in the irradiation time required for lower UV irradiances, there was no significant difference between the three conditions when normalized to the accumulated energy. This is confirmed by the values of the kinetics constants k (Table 2), with deviations in the order of their error interval. Similarly the inactivation of the E. coli at different volume ratio of 5; 7.5 and 10 and fixed irradiance of 40 W m-2 did not show significant differences (Figure 5b,


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Table 2). The shape of the curves was typical of bacteria disinfection as described by Marugan et al.20 The presence of the shoulder justified by a series of event phenomenon shows the cell damage is cumulative at 0-500 J L-1. The membrane cell undertakes a number of radicals’ attacks resisting thanks to self-defense and auto repair mechanisms. Then the bacteria inactivation gets accelerated and the membrane gets perforated. The tail at the end corresponds to an inhibition phenomenon produced by the competition of by-products released by the bacteria in the medium9. The results suggest that the disinfection process kinetics had the same pattern in the studied UV irradiance range and total-to-illuminated volume range. In all cases, an inactivation in the order of 5-log was reached after 3 kJ L-1 and the temperature remained at 25-30ºC along the experiment. On the contrary, Helali et al.21 reported a 5-log inactivation of E. coli in saline water after 1 kJ L-1 using 0.1g L-1 of TiO2 P25 in a solar batch reactor while increasing the temperature from 25 to 40ºC. This beneficial solar mild heating is in agreement with Ortega Gomez et al.22 who reported that an increase in temperature lead to an improvement in the disinfection process. Sichel et al.17 reported a 5 log decay of E. coli after an accumulated energy of 3 kJ L-1 solar TiO2 photocatalysis using an immobilized catalyst. These apparent discrepancies point out the strong influence of water composition and operational parameters such as temperature under uncontrolled natural solar light on the experimental results of disinfection. This confirms the usefulness of a large scale solar simulator when tunable irradiation conditions are required to improve the reproducibility and accuracy of data used for kinetic modelling and predictive reactor design. Results indicate that UV irradiance and total-to-illuminated volume ratio had a minor effect on the treatment efficiency under the studied range of conditions suggesting a rate photo-limited behavior due to the chosen load of TiO2. According to Sichel et al.23 disinfection is not exactly


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proportional to the accumulated energy and there is a minimum dose of UV photons required to produce certain level of disinfection. Below this, there is a correlation between disinfection yield and UV irradiance and above, disinfection remains similar regardless of the irradiance. In agreement with that, our results suggest that UV irradiances above 20 W m-2 leads to a direct correlation between bacterial inactivation and accumulated energy, although a different behavior should not be discarded for lower UV irradiance values.

4.3. Validation with natural solar light Figure 6 shows the results of bacterial inactivation under natural sunlight. In comparison with the results in the solar simulator, a comparable inactivation of about 4-logs is achieved after 3 kJ L-1 of accumulated energy. Moreover, the value estimated for the kinetic constant of 0.016 L J-1 (Table 2) is within the error interval of values calculated with simulated solar light. This validation supports the applicability of the developed large scale solar simulator for the prediction of the behavior of solar photocatalytic processes under well controlled radiation conditions.

4.4. Emerging contaminant degradation Figure 7 summarizes the averaged results achieved for emerging contaminant degradation during the bacterial inactivation experiments shown in previous sections. Comparison of results for 20 µg L-1 of initial concentration under simulated solar light (Figure 7a) and natural sunlight (Figure 7b), showed that similar moderate removal efficiencies in the average of 20 to 40% were achieved. However, data scattering was significantly broad, with negligible degradation of


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several compounds whereas others such as ranitidine (RNT), progesterone (PGT) or caffeine (CFN) were removed beyond 50% of conversion. Moreover, reproducibility of results was really poor, with error intervals in most cases including zero. It has to be taken into account, that despite the low concentrations of the micropollutants, the presence of ions and organic matter in the water involved a hard competition for adsorption sites and hydroxyl radical scavenging5 that decreased the efficiency of the photocatalytic process in comparison with ideal solutions of these compounds in deionized water. In contrast, Figure 7c shows that when the initial concentration of the pollutants is sufficiently low, in the order of nanograms per liter as it usually appears in real non-spiked waters, it is possible to achieve a removal efficiency above 80% after 3 kJ L-1 of accumulated energy. Consequently, even in complex water matrices with ions and organic matter, the solar photocatalytic disinfection process was able to simultaneously remove persistent pollutants rarely degraded in wastewater treatment plants such as carbamazepine (CZP)24, using the accumulated energy values required for the inactivation of 5-logs of bacteria.

5. Conclusions An innovative solar simulator was fully described and validated against the use of natural sunlight in photocatalytic disinfection applications with simultaneous removal of emerging contaminants.. UV irradiance and total-to-illuminated volume ratio showed no impact on the dependence of the bacteria inactivation kinetics on the energy accumulated in the system, indicating that the possible existence of dark repair mechanisms can be neglected within the studied irradiance range (20-60 W m-2). Summarizing, after 3 kJ L-1 of accumulated energy, 5logs of E. coli bacteria are inactivated whereas a removal efficiency above 80% is achieved for the micropollutants.


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ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness (MINECO), in the frame of the collaborative international consortium WATERJPI2013 – MOTREM of the Water Challenges for a Changing World Joint Programming Initiative (Water JPI) Pilot Call. The development of the large scale solar simulator has been also partially financed by the European Commission under FP7 project 309846, “Photocatalytic Materials for the Destruction of Recalcitrant Organic Industrial Waste – PCATDES” and Comunidad de Madrid through the program REMTAVARES (S2013/MAE2716). Thanks are also due to Dr. José Gonzalez from IMDEA Energía for his help with TracePro software and to Dr. Pilar Fernández Ibáñez from Plataforma Solar de Almería for her assistance in the design of the CPC collector.

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(4) Marugán, J.; van Grieken, R.; Pablos, C.; Sordo, C. Analogies and differences between photocatalytic oxidation of chemicals and photocatalytic inactivation of microorganisms. Water Res. 2010, 44(3), 789. (5) Pablos, C.; Marugán, J.; van Grieken, R.; Serrano, E. Emerging micropollutant oxidation during disinfection processes using UV-C, UV-C/H2O2, UV-A/TiO2 and UV-A/TiO2/H2O2. Water Res. 2013, 47, 1237. (6) Matsunaga, T.; Tomoda, R.; Nakajima, T.; Wake, H. Photoelectrochemical sterilization of microbial cells by semiconductor powders. FEMS Microbiol. Lett. 1985, 29, 211. (7) Herrera Melián, J.A.; Doña Rodríguez, J.M.; Viera Suárez, A.; Tello Rendón, E.; Valdés do Campo, C.; Araña, J.; Pérez Peña, J. The photocatalytic disinfection of urban waste waters. Chemosphere 2000, 41, 323. (8) Rincón, A.G.; Pulgarín, C. Photocatalytical inactivation of E. coli: effect of (continuous– intermittent) light intensity and of (suspended–fixed) TiO2 concentration. Appl. Catal. B: Environ. 2003, 44, 263. (9) Benabbou, A. K.; Derriche, Z.; Felix, C.; Lejeune, P.; Guillard, C. Photocatalytic inactivation of Escherischia coli. Appl. Catal. B Environ. 2007, 76, 257. (10) McCullagh, C.; Robertson, J.M.C.; Bahnemann, D.W.; Robertson P.K.J. The application of TiO2 photocatalysis for disinfection of water contaminated with pathogenic microorganisms: A Review. Res. Chem. Intermed. 2007, 33, 359.


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(11) Malato, S.; Fernández-Ibáñez, P.; Maldonado, M. I.; Blanco, J.; Gernjak, W. Decontamination and disinfection of water by solar photocatalysis: Recent overview and trends. Catal. Today 2009, 147, 1. (12) Malato, S.; Blanco, J.; Vidal, A.; Richter, C. Photocatalysis with solar energy at a pilotplant scale: an overview. Appl. Catal. B Environ. 2002, 37, 1. (13) Manassero, A.; Satuf, M. L.; Alfano, O. M. Evaluation of UV and visible light activity of TiO2 catalysts for water remediation. Chem. Eng. J. 2013, 225, 378. (14) Pablos, C.; Marugán, J.; van Grieken, R.; Adán, C.; Riquelme, A.; Palma, J. Correlation between photoelectrochemical behaviour and photoelectrocatalytic activity and scaling-up of P25-TiO2 electrodes. Electrochim. Acta 2014, 130, 261. (15) Kositzi, M.; Poulios, I.; Malato, S.; Caceres, J.; Campos, A. Solar photocatalytic treatment of synthetic municipal wastewater. Water Res. 2004, 38, 1147. (16) Van Grieken, R.; Marugán, J.; Sordo, C.; Pablos, C. Comparison of the photocatalytic disinfection of E. coli suspensions in slurry, wall and fixed-bed reactors. Catal. Today 2009, 144, 48. (17) Sichel, C.; Blanco, J.; Malato, S.; Fernández-Ibáñez, P. Effects of experimental conditions on E. coli survival during solar photocatalytic water disinfection. J. Photochem. Photobiol. A: Chem. 2007, 189, 239. (18) Cushnie, T. P. T.; Robertson, P. K. J.; Officer, S.; Pollard, P. M.; McCullagh, C.; Robertson, J. M. C. Variables to be considered when assessing the photocatalytic destruction of bacterial pathogens. Chemosphere 2009, 74, 1374.


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(19) Pablos, C.; Van Grieken, R.; Marugan, J.; Muñoz, A. Simultaneous photocatalytic oxidation of pharmaceuticals and inactivation of Escherichia coli in wastewater treatment plant effluents with suspended and immobilized TiO2. Water. Sci. Technol. 2012, 65(11), 2016. (20) Marugán, J.; van Grieken, R.; Sordo, C.; Cruz, C. Kinetics of the photocatalytic disinfection of Escherichia coli suspensions. Appl. Catal. B: Environ. 2008, 82, 27. (21) Helali, S.; Polo-López, M. I.; Fernández-Ibáñez, P.; Ohtani, B.; Amano, F.; Malato, S.; Guillard, C. Solar photocatalysis: A green technology for E. coli contaminated water disinfection. Effect of concentration and different types of suspended catalyst. J. Photochem. Photobiol. A: Chem. 2014, 276, 31. (22) Ortega-Gómez, E.; Fernández-Ibáñez, P.; Ballesteros Martín, M. M.; Polo-López, M. I.; Esteban García, B.; Sánchez Pérez, J. A. Water disinfection using photo-Fenton: Effect of temperature on Enterococcus faecalis survival. Water Res. 2012, 46, 6154. (23) Sichel, C.; Tello, J.; de Cara, M.; Fernández-Ibáñez, P. Effect of UV solar intensity and dose on the photocatalytic disinfection of bacteria and fungi. Catal. Today 2007, 129, 152. (24) Fagan, R.; McCormack, D. E.; Dionysiou, D. D.; Pillai, S. C. A review of solar and visible light active TiO2 photocatalysis for treating bacteria, cyanotoxins and contaminants of emerging concern. Mat. Sci. Semicon. Proc. 2016, 42, 2.


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Table 1 Bacterial inactivation kinetic constant k (s-1) a Ultrapure water

Saline water

SWTP water

Laminar

0.062 ± 0.02

0.093 ± 0.03

0.024 ± 0.01

Transition

0.150 ± 0.04

0.089 ± 0.02

0.063 ± 0.02

Turbulent

0.234 ± 0.06

0.250 ± 0.07

0.030 ± 0.01

a

Calculated using a kinetic model based on a series event disinfection mechanism20 (K = 0.5

mLn CFU-n; n = 1.14).


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Table 2 Bacterial inactivation kinetic constant k (L J-1) a VR 5

VR 7.5

20 W m-2

0.027 ± 0.007

0.019 ± 0.005

40 W m-2

0.014 ± 0.004

0.015 ± 0.004

0.020 ± 0.005

60 W m-2

0.020 ± 0.005

0.015 ± 0.004

Natural Sunlight

0.016 ± 0.004

a

VR 10

Calculated using a kinetic model based on a series event disinfection mechanism20 (K = 0.5

mLn CFU-n; n = 1.14).


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Figure 1 Scheme of the photoreactor (see text for details).


19


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Figure 2 Photograph of the cinema project used as lamp holder (top left), the CPC reactor illuminated with the simulated solar light (top middle), the CPC reactor illuminated with solar light (top right), a detail of the xenon lamp and reflector (bottom left) and comparison of the spectral distribution of the light provided by the solar simulator with the solar light in a sunny day.


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Figure 3 Radiation distribution of light arriving at the CPC surface under different lampreflector positions. Third at the top right was the optimal distribution of radiation.


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Viable E. coli, C/C0

1.E+00

1.E-01 Laminar Transition Turbulent 1.E-02

1.E-03 0

20

40

60

80

100

80

100

80

100

Time (min)


1.E+00

1.E-01 Laminar Transition Turbulent 1.E-02

1.E-03 0

20

40

60

Time (min) 1.E+00


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.E-01 Laminar Transition Turbulent

1.E-02

1.E-03 0

20

40

60

Time (min) Figure 4 Bacterial inactivation under different fluid dynamics conditions in a) ultrapure water; b) saline water; and c) SWTP water. Fitting lines were calculated using a kinetic model based on a series event disinfection mechanism20.


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1.E+00


1.E-01 20 W/m² 40 W/m² 60 W/m²

1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 0

1000

2000

3000

4000

5000

Accumulated Energy (J/L) 1.E+00


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.E-01 VR 5 VR 7.5 VR 10

1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 0

1000

2000

3000

4000

5000

Accumulated Energy (J/L) Figure 5 Photocatalytic bacterial inactivation in STWP effluent at a) varying UV irradiance and fixed total-to-illuminated volume ratio (VR) of 7.5; b) varying VR and fixed UV irradiance of 40 W m-2. Fitting lines were calculated using a kinetic model based on a series event disinfection mechanism20.


23


1.E+00


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 0

1000

2000

3000

Accumulated Energy (J/L) Figure 6 Photocatalytic bacterial inactivation under natural sunlight. Fitting line was calculated using a kinetic model based on a series event disinfection mechanism20.


24

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Removal efficiency, (C0-C)/C0

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

AAA ACF ATN CFN CZP DCF GFZ HCT IBP IPT PGT MTM RNT 0

0.3

0.8

1.6

2.5

Removal efficiency, (C0-C)/C0

Accumulated energy (kJ/L) 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0


0.4

0.8

1.6

2.1

3

2.1

3

Accumulated energy (kJ/L) Removal efficiency, (C0-C)/C0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0


0.4

0.8

1.6

Accumulated energy (kJ/L) Figure 7 Photocatalytic degradation of emerging contaminants under: a) simulated sunlight (C0 = 20 µg L-1); b) natural sunlight (C0 = 20 µg L-1); c) natural sunlight (C0 = 1 µg L-1).


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For Table of Contents Only


26

Photocatalytic Disinfection and Removal of Emerging Pollutants from

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