Storage for Photochemical and Energetic …...1.2. Innovative eco-fluid for CSP and thermocline...

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AXIS 2: CONVERSION, STORAGE AND TRANSPORT OF ENERGY. | Storage for Photochemical and Energetic Helioprocesses

Storage for Photochemical and Energetic Helioprocesses

Identity Composition of the team (or participants) Team leader: V. Goetz, (DR CNRS) Permanent personnel: X. Py (PR UPVD), D. Sacco (PR UPVD), P. Neveu 50% (PR UPVD), G. Plantard (MDC UPVD), R. Olives (MDC UPVD), Q. Falcoz 50% (MDC UPVD), N. Sadiki (Conv. Educ. Nat.), G. Hernandez 50% (AI CNRS), J.M. Mancaux (IGE UPVD) Not permanent personnel : Post Doc : F. Delaleux (12 mois, 2012/2013), F. Motte (12 mois, 2012/2013) PhD students: (1) achieved thesis: A. JeanJean (10/06/2013), A. Meffre (27/06/2013), S. Jacob (22/11/2013), K. Elatmani Co-tutelle (15/06/2013), A. Kéré (14/03/2014), G. Dejean (12/09/2014), M. Brienza Co-tutelle (12/03/2015), M. Kacem (07/07/2015), M. Miguet (20/11/2015), J.F. Hoffmann (03/12/2015) (2) thesis in progress: H. Espargillière (02/2013), T. Nahhas (03/2013), A. Rosset Co-direction (09/2013), C. Télégang Co-tutelle (09/2013), C. Zhou Co-direction (04/2015), E ; Kenda Co-Tutelle (09/2013), T. Fasquelle Co-direction (10/2014), Y. Seshie Co-tuelle (09/2013), A. Benberrah Co-direction (03/2014), C. François Co-direction (10/2014), N. Lopez-Ferber Co-direction (11/2015) Staff under contract: J.M. Mancaux (18 Mois 2011/2013 Keywords Storage – Advanced oxydation - Water – Energy – Wastes Topics Store energy at high temperature and improve the environmental impact of CSPs. Water treatment with advanced oxidation. Collaborations National - S. Chiron (HSM, Montpellier), S. Brosillon (IEM, Montpellier), N. Wery (LBE, Narbonne), C. Calas (Images, Perpignan),

F. Maury (Cirimat, Toulouse), J. Pruvost (GEPEA, Nantes), J.F. Cornet (Institut Pascal, Clermont Ferrand), A ; Nzihou (Rapsodee, Albi), C. Bessada (CEMHTI, Orléans), Dupont C. (CEA, LITEN, LTB, Grenoble), J. Walker (Arkéma, Lyon), M. Muselli (SPE, Corse), F. Delaleux (CERTES, Lieusaint), B. Cagnon (ICMN-CRMD, Orléans), O. Vidal (ISTerre, Grenoble), F. Ricci (Art-Dev, Montpellier), J.-F. Henry, M. Chirtoc (GRESPI/LTP, Reims).

- Y. Jaegger (Véolia, Montpellier), C ; Bourdil (EDF, Paris), G. Jeangros (Aqylon, Paris), A. Meffre (ETC, Perpignan), Da Silva Perez D. (FCBA, Pôle NMA, Grenoble), D. Rochier (Exosun, Mansle).

International - J. Blin (2iE-Cirad, Burkina Faso), S. Bufo (Univ. Basilicata, Italie), B. Rhouta (Univ. Marrakech, Maroc), L. Cabeza

(GREA, Univ. Lleida, Espagne), D. Yamegueu (LESEE-2iE, Burkina Faso), A. Romagnoli (NTU, Singapour). - N. Calvet (Masdar Institute, EAU) Contracts - ANR Stock-E: « SACRE», 2010, 42 months (Partner). - European project China-EU « ICARE », 2010, 60 months (Partner) - European project 7 ième PCRD: « OPTS», 2011, 36 months, (Partner). - Contract CNRS Institut technologique FCBA n° 0599822010, 2011, 36 months - Contract CNRS-EDF n° 62893 : 2012, 36 months. - Contract CNRS-Aqylon-EDF n°87698 + Amendment n°1 et n°2, 2012, 36 months. - Contract CNRS-Véolia n°84294, 2012, 36 months. - ANR SEED: « DRYRSP », 2013, 48 months (Coordinator). - Communauté de Travail des Pyrénées: 2013, 24 months (Coordinator).

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- Project DEFI CNRS « PaleoStock », 2013, 12 months (Coordinator) - Research and collaboration contract CNRS-Université de Basilicata n°CT 085385 et n°CT 094167 ; 2012 +

Amendment for 1 year in 2013, 18 months. - Chercheur d’Avenir Région LR : « Hybridation procédés membranaires AOPs » ; 2013, 24 months (Coordinator). - European project H2020, « SOLAREUROMED », 2013, 48 mois (Partenaire) - PHC Toubkal Franco-Marocain n°30339QC: « Photocatalyseurs sur argiles naturelle» ; 2014, 36 months (Partner). - European project H2020, « INPATH-TES », 2015, 36 months (Partner). - Defi-ENRS - ReMinER, 2014, 48 months (Partner) - Research and collaboration contract CNRS-IRD n°134844, « Isote-Ph7 », 2015, 6 months (Partner). References 14, 15, 21, 27, 28, 29, 38, 48, 58, 67, 71, 72, 74, 79, 83, 89, 118, 130, 132, 142, 144, 206, 230, 249, 250, 251.

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Scientific report INTRODUCTION

Water and energy are the two raw materials essential to the development of the human community. They are closely related, highly interdependent and advances, new developments, regulation adopted in one of these two fields impact directly or indirectly the other one. The amount of water needed to produce power depends on the process selected for energy production. Anyway, it is essential in all cases to minimize this consumption especially in water-stressed areas where energy is in direct competition with other end users (irrigation, industry, drinking water ...). Wastewaters, previously considered as 'waste' are now starting to be considered as a resource of interest for the production of biofuel or for heat recovery applications. Re-use for irrigation leads to energetic but also significant economic gains. Beyond specific examples, the set water-energy-waste is a particularly favorable framework for implementation of the circular economy which addressed through the prism of solar energy, leads to the concept of eco solar-technologies. It defines the priority number 4 of the labex Solstice to which belongs Promes the laboratory, and corresponds the general framework of the approach adopted in the SHPE team. The objective assumed as applied is to take advantage of the added value of combining the solar resource with items of the triptych water-energy-waste. Based on collaborations, particularly in the specific field of waste valorization (RAPSODEE Mines d'Albi, Solstice partner), we tend to develop a multidisciplinary approach based on process and materials engineering. Given this general objective, two themes are particularly studied. The first is part of a set of proposals that are intended to improve the environmental impact of concentrating solar power plants which are "the core activity" of PROMES. The main research development in relation with these items is focused on high temperature energy storages system based on wastes valorization. It is completed by approaches included in the triangulation water-energy-waste: reduce water consumption of CSP plants that is one of the critical points; test sustainable transfer fluids. The second theme, part of the water treatment field is solar advanced oxidation of effluents contaminated with pathogens and/or organic chemical pollutants. This process advantageously coupled with separation process with adsorption provides a unique opportunity to improve significantly the sanitary level of effluents considered as wastes with no additional primary energy consumption for reuse in the case of irrigation as example. The scientific questions raised by these research activities will be detailed in the various sub-topics. However in the considered period (2013-2015), this approach has yielded to significant advances embodied in particular by: (i) the business creation of the Startup EcoTechCeram (ETC) by Antoine Meffre former PhD student of the team , winner of the World Innovation Contest and whose objective is the production of ceramics from different end of life cycle materials: asbestos waste, fly ash, slag from steel, ...; (ii) the implementation by Veolia of a scale one facility (directly coming from a collaboration as part of a Cifre PhD) of drinking water from a groundwater contaminated with volatile organic compounds. Drinking water is obtained by separation with adsorbent column. This step is part of the research on the development of a sustainable water treatment system including separation, adsorbent regeneration using solar energy and mineralization of pollutants by solar advanced oxidation.

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Summary

1. Store energy at high temperature and improve the environmental impact of CSPs.

1.1. High temperature ceramics produced from inorganic industrial wastes

1.2. Innovative eco-fluid for CSP and thermocline storage.

1.3. Reduction of water consumption in CSP

2. Water treatment with advanced oxidation

2.1. Micro-pollutants and pathogens solar oxydation

2.2. Sustainable drinking water production

2.3. Visible photo-activated material

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1. STORE ENERGY AT HIGH TEMPERATURE AND IMPROVE THE ENVIRONMENTAL IMPACT OF CSPS.

1.1. High temperature ceramics produced from inorganic industrial wastes The development of solar power plants (CSPs) needed for the energetic transition is of the order of 10% of the worldwide mix in 2050. On the technical point of view, this can be easily reached by the CSPs whose recent achievements such as Andasol or Gemasolar have fully demonstrated their level of maturity. However, recent life-cycle assessment studies and the corresponding mineral resources requirements have shown that the environmental footprint of these technologies can be advantageously reduced and that some needed resources could be a limiting factor or highly impacted. This is particularly the case for sensible heat storage based on molten nitrate salts, historically developed at Themis and now applied to most of the CSPs. This thermal storage represents 20% of the environmental footprint of the process and the 2050 stakes exceed the world production of natural nitrates. This led the laboratory to suggest alternative option firstly developed in the ANR-Solstock program. The global objective of this innovative approach is to tend to replace the major part of these salts by ceramics elaborated from recycled wastes. Various inorganic industrial wastes were tested in the ANR Solstock, SACRE and SESCO and OPTS, Eurosunmed European programs: asbestos waste, fly ash (from coal power plant or waste incinerator) bottom ash, metallurgical slag. Slag products being initially in the molten state, they present an additional advantage. These wastes are heated to temperature from 1000 to 1400 ° C and then subjected to controlled cooling to obtain: (i) the appropriate crystal structure; (ii) the desired shape of the storage module (Fig. 1) facilitating heat exchange with heat transfer fluids while minimizing the HTF pressure drops. Despite the energy needs of the treatment of the wastes, the high temperature storage applications allow an environmental pay-back time below 2 years. A comparative life-cycle assessment between conventional storage technology and the proposed alternative has been achieved and demonstrates the soundness of the approach. Ceramics thus obtained were characterized in terms of thermophysical and thermomechanical properties. They have functional properties comparable to commercial ceramics such as mullite, develop exceptional thermo-mechanical properties in terms of resistance to stress during cycling and thermal shock resistance up to 1000 ° C. This study was an opportunity to initiate, in collaboration with the GEMH (Limoges), a new activity in the laboratory for the characterization of ceramic storage or solar receiver with ultrasonic and acoustic emissions. Recycled storage ceramics have also been studied in terms of compatibility with the heat transfer of fluids in operation in the concerned processes (oil, molten salt, compressed hot air at atmospheric pressure) and tested on a pilot scale according to different geometries. On the industrial point of view and in term of resources availability, the deposit of inorganic wastes is far higher than the storage material requirements and obtained ceramics are 4 to 1,000 times less expensive than synthetic product proposed on the market. Very recently, this research item has been extended to the formulation with not only a single initial waste but a mixture of co-products possibly supplemented with a natural product. This is the case of the materials developed for the project CSP4Africa with 2iE for which mixtures of bottom ash from coal thermal power plant, slaked lime from acetylene industry and laterites are operated. In another aspect, the thermal conductivity of ceramics (including recycled ceramic) devoted to sensible heat storage is often low, on the order of 1.5 W/(m K). SiC is recognized as developing high conductivity at high temperature. Then, the approach previously implemented was applied to test formulation within the objective to develop 100% SiC ceramics elaborated from industrial co-products. This emerging subject has already allowed achieving 30% SiC ceramics - (Figure 2) 70% mullite exclusively from waste while reducing advantageously by 20% the synthesis temperature. This work was awarded in 2011 (price of Innovative Techniques for the Environment, Pollutec-ADEME), in 2015 (DERBI competitiveness cluster science prize) and as part of the Global Innovation Competition MIC-1 2014 and CMI- February 2015 for the Start-Up "Eco-Tech Ceram" created by Antoine Meffre, former PhD student of the SESCO program.

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Figure 1 : Thermal energy storage module made of inorganic industrial wastes.

Figure 2 : Recycled ceramic containing 30% SiC - 70% Mullite elaborated form industrial wastes.

1.2. Innovative eco-fluid for CSP and thermocline storage Ceramics elaborated from industrial wastes are a sustainable option to the key issue of solids able to provide large scale sensible heat storage likely to work at temperatures of several hundred degrees ° C. Today, the air is the heat transfer fluid (HTF) which allows to consider to run heat storage at temperatures up to 800°C. Molten salts are commonly involved in storage systems for CSP and synthetic thermal oils are used as HTF in numerous facilities that reach temperatures of 400°/500°C. The use of ORC cycles for electricity production through solar energy allows considering installations operating at a moderate temperature of about 200°C, while reaching acceptable efficiency. In this temperature range the vegetable oil is a relevant candidate as sustainable HTF. Associated with ceramics elaborated from wastes, but also natural rocks that become compatible with these temperature levels, vegetable oil combines low operating costs with a highly favorable environmental balance. Determined on the basis of physico-chemical characterization, aging and compatibility tests (J. F. Hoffmann PhD), the true potential of vegetable oils has been one of the research objectives. It is included into the more general goal to implement innovative solutions to improve the environmental impact of solar power plants. Seven vegetable oils: rapeseed; soy ; sunflower; palm; coconut; cotton; jatropha; representing over 90% of world production now estimated at over 180 million of tons were subjected to a series of tests and characterizations at temperatures up to 250 ° C. This made possible to generate a new database previously not available in these temperature levels: the thermal conductivity; the specific heat (Figure 3); the dynamic viscosity; density; thermal stability and evolution of the fatty acid composition before and after aging at 250°C for periods of several months; have been systematically determined and correlated in the form of a function of the temperature. According all of these criteria, no bolts were highlighted. Vegetable oils and in particular rapeseed oil emerges as relevant HTFs in the case of operating temperature not exceeding 250 ° C. Beyond the acquisition of a set of correlations, this work has allowed identification of a relationship between the thermal stability T3 (Figure 4) of an oil and its acid index, an easily measured value that can be considered as a parameter that defines the need of replacement of part of the oil in an operating plant. Vegetable oils have very good physical and chemical compatibility with various storage materials, whether natural rock or ceramics developed from wastes. This allows achieving a coherent set for the definition of a thermocline storage bedrock bringing together economic and environmental advantages. Made with a single tank (which allows it to be economically competitive) this storage system nevertheless imposes a strict management of heat exchange between the solid and the heat transfer fluid. This, to ensure output temperatures compatible with the desired use (ORC cycle). In order to have a dimensioning tool, a thermocline system with a storage capacity of 10 kWh (Figure 5) was designed and tested.

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Figure 3 : Oil specific heat as a function of temperature. Figure 4 : Oil thermal stability as a function of the acid index. This facility makes it possible to perform charge and discharge cycles over periods ranging from 1 to 5 hours. Designed to work in a range from 150 ° C to 220 ° C, the pilot was experienced with rapeseed oil as a transfer fluid and quartzite as solid. A series of operating conditions and more particularly the particle sizes and the fluid velocity have been tested. Indeed, the latter is the key parameter that determines the size of the thermocline area which is the area of high temperature gradient. And this is the establishment of a thermocline or temperature front within the tank (Figure 6) which guarantees a sufficiently high and stable output temperature thus leading to an efficient storage system. Such thermocline is effective only in the case of highly laminar regimes for Reynolds numbers of the order of ten corresponding to velocity of the order of a millimeter per second. In the best cases, this demonstrator reached an efficiency of about 70% corresponding to a thermocline height of 0.8 m. 70% of the heat stored initially at 210 ° C was thus delivered at a temperature above 200 ° C. Understanding a thermal system needs experimentations but also modeling. In the case of a tank working on the principle of the thermocline, a 1D formalism is adequate to account for the temperature profiles in the fluid in the flow direction. Discretization of the solid particles is not required subject to compliance with the Biot number low enough. A 1D model accounting for two phases (liquid and solid) was validated on the basis of systematic experiment / simulation comparisons of local variables (temperature profiles in the tank and at the exit of the latter), but also on thermal storage efficiency. The relevance of this model was further confirmed through comparison with results from large scale experiments conducted at Sandia laboratory and at the Solar One plant (USA).

Figure 5 : Experimental set up (before insulation): 10 kWh of storage with 500 kg of quartzite and rapeseed as heat transfer fluid

Figure 6 : Axial experimental and simulated (continuous lines) temperature profiles during a discharge: particles diameter = 15 mm; mass flow = 20 10-3 kg/s.

This approach is being extended to other couples HTF/solid within the objective to have a series of options that will provide thermocline storage adapted throughout the CSP temperature range, but also to the local available resources. In this way, the laterite abundantly available in african soil is currently studied as solid storage in the context of a collaboration with 2iE (E. Kenda PhD). Granit, highly available in the egyptian soil is tested as part of the European SolarEuromed project. (N.

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Tamar PhD). Compatibility of ceramics elaborated from wastes with "more conventional" transfer fluids such as molten salts and synthetic thermal oils is also characterized on a dedicated set up. Finally, the work on the thermocline goes on at Odeillo site with the integration of a tank in a complete loop implemented as part of the Equipex Solstice (T. Fasquelle inter-team PhD).

1.3. Reduction of water consumption in CSP Solar concentrating power plants (CSPs) operate on the Rankine cycle basis. They have a return of industrial experience of more than 30 years and since about ten years they are subject to an increase of dissemination. The cooling system of the CSP condenser is recently identified as a major technological bolttleneck. Each electrical MW product leads to about 2 MW of waste heat to be discharged at 55 ° C in the environment. As CSP are intended to be implanted in arid areas with hot surrounding temperature, the condensing temperature is often too close to the ambient temperature. Currently, this fatal heat is discharged using a wet cooling technology responsible for a significant water consumption (3.7 m3/MWh) or using air cooler inducing a decrease of the Rankine cycle efficiency and a high power consumption. In arid area, water resource is too valuable and its use for wet cooling can lead to a major conflict of use while air coolers make the process highly dependent on the ambient temperature. In the case of power plants operating at lower temperature range with organic cycles, the performance is even more affected by the cooling efficiency during condensation. The development of efficient dry cooling systems is therefore critical for the deployment of such technologies in highly sunny areas. The goal is then to design and validate an innovative system to extract to the heat of condensation without water consumption. Even, to cool down below the dry temperature to overcome the ambient temperature limitation and if necessary to produce water by condensation of air moisture during the night (H.Espargillière PhD). This approach was first studied in the ANR-DryRSP program and consisted into taking advantage of the existing solar field of the plant (not less than 50% of their investment) as a macro-heat exchanger. Extended heat exchange surfaces are then available for convective and radiative (with the space at 3 K via the atmospheric window) heat exchanges during the day and the night. This technology has been already patented by CNRS and Exosun, the two partners of the ANR program. Taking advantage of the historical works of Felix Trombe on radiative cooling of the earth surface by infrared radiation in the atmospheric window 8-14 µm, the project partners have first characterized current but also innovative reflective surfaces adapted to CSP facilities (Figure 7). These characterizations were performed on new surfaces but also on surfaces subjected to enhanced aging procedures. It is thus demonstrated that the traditional glass mirrors have adapted and better performance than metal mirrors but that the emerging reflective films have a high emissivity on the whole relevant spectral band. These surfaces implemented with the two objectives: solar radiation concentration; removal of the heat of condensation; have to be associated with a dedicated heat exchanger coupled to the heat transfer fluid (Figure 8). Innovative heat transfer fluid circuits are thus integrated on the rear side of the conventional reflective surfaces. Mastering the simultaneous heat exchanges needs to optimize the fluid circuit for an optimal heat dissipation. The thermodynamic analysis and the constructal approach are relevant to carry out such an optimization. This is a large field of study far from being fully explored. The resulting innovative optics are tested for different weather conditions. It helps to justify the integration of new materials in the design of CSP solar fields, integration that today remains rather slow Based on the linear Fresnel CSP-type geometry, a comparison is under progress from the most simple type tube-fin configuration to the most innovative configuration corresponding to a structured type roll bond heat exchanger. The experiments were carried out under various climatic conditions (Perpignan, Ajaccio, Burkina Faso) and in various modes (thermal dissipation with fluid flowing, static cooling down for water production). The results, both experimental and simulated, demonstrate that the suggested approach can effectively dissipate the heat generated for condensation without water consumption and without impacting the performance of the process. At Perpignan, without optimal weather conditions for radiative exchange, we get an average power dissipation of about 50 W/m2 during night experiments, with peaks around 80-90 W/m2 for the most favorable conditions. The analysis shows that 250 W/m² are needed to dissipate all the waste heat, needs already covered by convective exchange in many cases. Therefore, radiative cooling may be also considered as an additional cooling potential allowing sub-cooling for the benefit of the Rankine cycle efficiency. When the concentrator is not powered by the fluid transfer from the condenser, the surface may then be sub-cooled and under favorable conditions, condense moisture from the air to produce then fresh water. This last feature, specialty of the SPE laboratory is currently studied experimentally on the site of Vignola.

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Figure 7 : Comparison of spectral emissivity for conventional and innovative reflective surfaces for CSPs..

Figure 8 : Prototype for radiative cooling with integrated back side heat exchanger

If the coldness is mainly produced during night by radiative effect, it must be stored and used during the day to ensure the expected cooling function (or condensing moisture and produce fresh water). Optimized management of time lag between needs and production in cooling then leads to suggest new way of the storage integration in CSPs. In this context, the thermal storage using phase change material can be a valuable asset due to the corresponding high energy density as well as its self-regulated temperature. Nevertheless, given the low thermal conductivity values of these materials in the range of 0.24 W/(m K), transfer intensification with fins or by addition of conductive materials is a prerequisite for designing a storage tank. For given fin geometries (Figure 9), optimization studies are being conducted within the DryRSP program based on the analysis of irreversibility in the material during charge and discharge steps. This work is a complement of previous studies performed on PCM / graphite composites at another scale.

Figure 9 : a: IR picture of a composite melting in the case of a T-shaped fin (left picture)

b: Comparison of numerical simulations during PCM melting in the case different fin shapes or for a composite PCM/graphite (right picture).

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2. WATER TREATMENT WITH ADVANCED OXIDATION

2.1. Micro-pollutants and pathogens solar oxydation The literature is now abundant on the subject of advanced oxidation processes (AOPs). It is significantly less important in the case of outdoor solar conditions, and becomes truly scarce on the subject of complex effluents. This is the result of analytical difficulties imposed by this kind of experiments that basically necessitates being able to detect mixtures of micro-pollutants at environmental concentrations included in complex matrices; what defines a research item as such. If mineralization of micro-pollutants is the physico-chemical process related to advanced oxidation, the practical objective of any detoxification operation is to lower the toxicity level of the effluent. On that topic also, given the concentration levels involved, the standardized toxicity measurement methods (such as Microtox) are often far to be adapted and specific biological techniques are the relevant tools to assess the effectiveness of treatment: measurements of estrogenic activity and/or genotoxicity have to be performed. Monitor various micro-pollutants in effluents, be able to quantify the level of toxicity of effluents, remains the ultimate goal necessary to achieve in order to qualify the efficiency of the advanced oxidation processes (solar) in the practical conditions of their use. This approach was therefore carried out by successive steps throughout, when necessary, collaborations with laboratories such as Hydroscience and the Institute of Membranes that have the required analytical skills. A first step was to monitor a specific endocrine disruptor, used as a pollution indicator, the 17 -estradiol, in an effluent collected at the outlet of a sewage treatment plant. These tests were carried out in outdoor conditions with one of the two solar set up available at Promes. They also made it possible to extend the area of expertise of the team beyond heterogeneous photocatalysis solar to the photo-Fenton-type AOPs which happens in homogeneous phase (M. Brienza PhD). Tests with the peroxymonosulfate as the oxidant associated with ferrous ions (Fe 2+) as the catalyst were performed. Indeed, radicals sulphate generation present the decisive advantages of an increase of the selectivity (if compared to hydroxyl radicals), the use of very cheap reagents with easy handling (solid reactants), this while maintaining the interest of oxidation in homogeneous phase which provides high mineralization kinetics. In a second step, series of experiments in homogeneous and heterogeneous phase were carried out on mixtures obtained with a solution doped by several pollutants. Whether a "cocktail" of pesticides (Clothianidin Mesotrione + + Bifenthrin) or pharmaceuticals compounds (Diclofenac + Carbamazepine Sulfamethxazole), mixtures representative of a very wide range of pollutants, AOP proved to be an effective process for their mineralization. It is a work at a laboratory scale, carried out on fifteen liter in outdoor conditions and on an effluent directly collected at the outlet of a water treatment which closed this part of our work. More than 60 micro-pollutants gathered by family of organic pollutants (antibiotics, antidepressants, anti-inflammatory, hormonal products, pesticides, ...) were initially detected in the effluent (Fig. 10). The major part of these pollutants either completely disappeared either were greatly affected after few hours under solar irradiation in the presence of oxidant. This result demonstrates that the advanced oxidation principle applied to a complex matrix, therefore necessarily highly charged with various organic products (30 mg/l), bicarbonate and nitrate, numerous and different ions (chlorine, calcium, sodium and potassium) ...., corresponds to a reality to eradicate many micro-pollutants present at concentrations much lower than the µg/l. This allows improving the environmental compatibility of the effluent lowering its endocrine disrupting activity. Beyond this demonstration, the objective is now to assess the performance with a small scale on site (outlet of a waste water treatment) system operating during several months.

Figure 10 : Group of emerging contaminants removed by solar advanced oxidation. (TiO2-solarUV ; PMS/Fe(II)/Solar).

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One of the advantages of AOPs is to offer the opportunity to carry out, without additional cost, a simultaneous decontamination (organic pollutants) and disinfection (pathogens). Over the period considered, the aspects of disinfection were discussed as part of the M. Kacem PhD done in close collaboration with the Environmental Biology Laboratory (LBE) of INRA-Narbonne. Among the four species that are now subject to regulation for the re-use of waste water for irrigation or spraying: fecal enterococci; RNA phages F-specific; spores sulfitoréductrices anaerobic bacteria; escherichia coli; only the last pathogen was selected for testing. This taking care to work with a harmless strain. The results obtained in this area, which are the first disinfection tests conducted in the laboratory, are therefore to be considered as "preliminary" results appropriate to supplement by campaigns measurements carrying on all the pathogens to master for re-use of wastewater. E. coli inactivation has been taken in terms of reactor engineering proposing a mechanism which is based on the coupling of transfer of the bacteria to an interface with the photocatalyst and an attack of the membranes by the radicals produced by the TiO2 under UV radiation (solar or artificial). The suggested model is thus based on a set of equation corresponding to: (i) an adhesion phenomenon, validated thanks to MEB pictures (Figure 11); (ii) an inactivation which takes place simultaneously in the liquid phase in the immediate vicinity of the catalyst and on the bacteria in adhesion with TiO2 particles. This writing has allowed accounting for inactivation rates (Figure 12) for different shape ratio bacteria/catalyst particles and for a wide range of operating conditions in terms of initial population of bacteria population and/or intensity of irradiation.

Figure 11 : E coli bond in the cases of a catalyst of higher or lower size.

Figure 12 : E coli experimental and simulated (continuous lines) concentration profiles. Degussa P25 suspension under different UV intensities (0 à 35 W/m2).

Efficiency of a disinfection operation is often assessed through the use of culture techniques. However, cells subjected to a stressful environment may sometimes temporarily lose their growing potential; it is called viable but non-culturable bacteria (VBNC). To avoid persistent phenomenon, it is essential to accurately describe the result of the free radical attacks. This was possible thanks to the combined use of cultivation methods and biological methods for DNA quantification: q-PCR and q-PCR associated with monazide propidium. The simultaneous use of these different ways of characterization has allowed suggesting an original approach that interests the process engineering as well as the biology and highlighting different rates for: (i) the inactivation of bacteria; (ii) the irreversible alteration of bacterial membranes; (iii) the final disappearance of the DNA corresponding to the remove of nucleotides. 2.2. Sustainable drinking water production Advanced oxidation processes (AOP) using solar allow to consider the treatment of a large number of pollution. They are very attractive because in perfect agreement with the sustainable development principle. However, the development of these technologies is still limited because of processing capacities which remain very low. As a consequence, these eco-processes environmentally friendly but also economically competitive are today only considered in the case of applications that generate low volumes to be treated. This is compatible with a spread in the southern countries, with high solar resources, with an electric network sometimes ineffective and that requires simple and treatment methods, with the lowest possible operating costs. But this is very detrimental if one’s wishes at middle or long term meet the requirements of the problem, considered today as very serious and worrying (and highlighted by a series of European directives frames), of micro-pollutants release at the outlet of wastewater treatment plants. Otherwise except ozonation which cannot be activated by solar energy and requires electricity consumption for reactive production, no AOP is now approved in Europe for the production of drinking water. For all of these reasons it is quite desirable to study the interest of hybridation with AOP with

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processes today well established in the global chain of water treatment. This, with the objective to overcome the difficulties mentioned above while retaining the environmental benefits linking to AOPs activated by solar energy. Coupling an advanced oxidation treatment with adsorption is an option of high interest. This leads to an efficient association of the high separation capacities of pollutants (but also pathogens) on adsorbent columns to a time lag and dissociation in space of the treatment of the pollution during longer periods by solar photocatalysis. This is the option that has been studied as part of a collaboration with Veolia society (M. Miguet PhD) with as middle term objective to offer a sustainable production chain for drinking water. Applied to the very specific case of producing drinking water from a polluted groundwater by perchloroethylene (PCE), the process is divided into three distinct steps: adsorption / separation of the pollutant on activated carbon column; thermal regeneration of the adsorbent with solar energy; mineralization of condensate issued from regeneration by solar photocatalysis. The first step was the subject of a full development. The laboratory results: isothermal adsorption measurements on a dedicated bench adapted to volatile compounds; test columns with determination of breakthrough curves; made possible to validate a model of sorption phenomenon in dynamic mode (Figure 13a). This model was used for the dimensioning by a pre-industrial pilot (treatment capacity of 1 m3/h) operating in real conditions (Figure 13b). The installation of scale 1 for treating a flow of 100 m3/h is currently in progress on the production site. Thermal regeneration by solar energy (Figure 13c) can be done, taking into account the necessary temperature levels, with a cylindrical-parabolic concentrator. Such regeneration avoids the replacement of the adsorbent once it is saturated. While not perfect, more than 60% of the initial capacity was recovered after five regeneration cycles (Figure 13c) which demonstrated the potential of this mode of regeneration in the case of volatile compounds. Finally mineralization of the condensate by solar AOP, the final stage was shown at the laboratory scale. Thanks to the concentration perchlorethylene carried out by adsorption prior regeneration, a one square meter of surface irradiated reactor over a period of one to two summer months is enough to remove the entire amount of the pollutant trapped during three months of operation of the pre-industrial column. The sequence of the three phases, allows to achieve the destruction of the pollutant with an extremely favorable environmental impact.

Figure 13a : Experimental and simulated PCE profils. Laboratory column (v=2 m/h).

Figure 13b : Pre-industrial pilot.

Figure 13c : Regeneration rate for Treg from 130 à 400°C.

Coupling oxidation/adsorption can also be addressed at the level of the adsorbent particle. This means the development of effective methods for elaboration of AC / TiO2 composites that keep the initial adsorption activated carbon properties and photo-catalyst activity. This kind of material has the dual functionality oxidation-sorption (Figure 14a). It allows considering in situ regeneration process. It also allows, subject to respect criteria of proportion and sizes of the two entities, to consider improved mineralization rates thanks to the natural concentration of the pollutant in the vicinity of the photocatalyst. A first series of composites tested is the result of collaboration with a Moroccan laboratory, the CLNM and CIRIMAT Toulouse (Prog Toubkal). These nanocomposites were synthesized by dry route with the combination of natural clays (developing properties of adsorbent) to the titanium sulphate used as a molecular precursor of TiO2 (obtained after activation in air at 600 ° C). A second series of composites were synthesized through a PhD supervised jointly with 2iE Faso Burkina (C. Telegang PhD). In the latter case, the adsorbent is first prepared by conventional activation pathways with locally available biomass, wood eucalyptus or shea. Then it is associated by coating with a titanium sol available commercially. In both cases, the materials obtained are characteristic of the interest of this association that provides a real modularity of the properties. The photocatalyst supported on clay joined processing rates obtained with the Degussa P25 powder that is considered as the reference in heterogeneous catalysis. The second material enables the development of composites with conventional properties of adsorption while exhibiting a mineralization function of the pollutant (Figure 14b).

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Figure 14a : Mechanism of pollutant disappearance from the liquid phase in the presence of the composite..

Figure 14 b : Phenol concentration in a solution in contact with a compsite (AC/TiO248%) with and without UV

The principle added value of a coupling between solar AOP to a process well established in the field of water treatment was also explored in the case of membrane separation. With the local Languedoc Roussillon funding “Futur Researcher”, Promes laboratory and the European Membranes Institute collaborate to assess the interest of a solar AOP / membrane process hybridization. Apply to effluents coming from wastewater treatment that contain many micro-pollutants at very low concentrations, the membrane process ensures the separation of these contaminants and offers the possibility to store them in a liquid phase at a much higher concentration; This storage can smooth inflows to be treated. The second step consists of treating these highly concentrated effluents namely bio-recalcitrant pollutants that could in fact not be treated by conventional biological process. We show that this hybridization ensures mineralization of organic pollutants leading to a large decrease of their resistance to biological attacks. After treatment the effluent may potentially be released into the environment or returned to waste water treatment head. Ultimately, it is able to offer a production with zero pollutant rejected. 2.3. Visible photo-activated material Our research activity is built around the use of solar resource that involves managing discontinuity but also the low availability of radiation in the UV range. This part of available radiation, a maximum flux density of 50 W.m-2 during beautiful sunny days, represents only 5-7% of the overall radiation while 50% for example in the visible range. Photocatalytic semiconductors performances currently commercially available or developed in the laboratory are unsuitable and make it almost prohibitive any large-scale development of the photocatalytic processes. These low performances are linked to the mechanism of this oxidative process that involves three key steps. A first step of photo-excitation consists of photon absorption by a semiconductor which occurs when the energy content of photons is high enough to excite electrons from the valence band to the conduction band creating an electron/hole. During the second step, the pair of loads has the ability to migrate to the surface or recombine according to various processes. The last step is the oxidation-reduction reaction at the catalyst surface. Currently, our work is at the level of the first two stages that are considered as the mainly causes of low yields catalysts and which are the subject of numerous studies. The efficiency of the catalysts can be defined by the performance that informs about the number of charges actually available to produce radicals on the initially number of photo-generated charges. To understand the mechanisms involved, one’s has to be able to: (i) describe the transfer of radiation taking place in the heterogeneous water/solid catalyst; (ii) the process of photo-excitation and load migration to initiate redox reactions. Understanding the radiative transfer in the reactive medium is discussed experimentally and theoretically. Optical measurements for strongly scattering media such as catalyst suspensions, foams coated catalyst, fibers .... are performed using a bench consisting of a solar simulator emitting a collimated source, a spectrophotometer coupled with an integrating sphere. The objective is to experimentally quantify the effective optical properties of the medium that are the absorption, transmission and reflectivity. These experimental results are compared with those obtained by the radiative model developed by C. Calliot thanks to collaboration with the team TRECS. This is to identify the optical properties of different media and to have an access to the local values of radiations. This approach will make it possible to evaluate the optical performance of the catalyst. It is the number of photons interacting with the catalyst efficiently and therefore actually available for a photo-excitation of the catalyst leading to the creation of an electron/hole pair.

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To increase the performance of the solar oxidation, it is essential to significantly enhance the performance of the catalyst greatly limited by the recombination process. In literature the proposed routes are to increase the number of effective photons by broadening the useful spectral band to the visible range. To address this issue, we work with different partners (LGC, CIRIMAT), and in particular with the PPCM team of the laboratory, that masters the methods of synthesis of nanocatalysts and associated characterization tools. Our approach is to implement catalysts and evaluate their performance under different conditions of irradiation namely UV only, visible or solar to discriminate the operating wavelength ranges and the elaboration route of the corresponding composites. This collaboration builds on the A. Rosset jointly supervided PhD is in two parts - a first part which is to master the synthesis of photocatalytic nanoparticles defining the optimal condition for elaboration and - a second part which corresponds to an experimental measurement of the catalysts photocatalytic efficiencies. The method of preparation of zinc oxide nanocatalyst, selected as the reference material is based on an sol-gel elaboration route. The sol is dried in supercritical conditions and calcined to activate the catalyst. Structural (SEM, DRX) and optical (reflectivity) properties are characterized to meet the standard of elaboration. Special attention is paid to the size and the crystal lattice of the catalyst nanoparticles (Figure 15). To have a real influence on the yield, catalyst/dopant agent alloys were synthesized by varying the synthesis conditions (temperature, type of precursor ratio solvent/precursor) for the catalyst and the doping substance (type and composition). In comparison with the existing literature, a very wide spectrum of dopant and composition were tested. For example, tests have been performed on a series of doping belonging to different families (alkali, alkaline earth metals, transition metals, organic ....) and a further study was performed on the Zn(1-x)OCax obtained from different precursors and for compositions (x) ranging from 0.01 to 0.2.

Figure 15a: Photographs taken at Scanning Electron Microscope of Zn0.9Ca0.1O calcinated at 573°K.

Figure 15b: DRX patterns of selected nanoparticles for various elaborated catalysts obtained by the sol-gel method and calcined at 573°K (a) Zn0.95Ca0.05O, (b) Zn0.99Ca0.01O (c) CuInSe2, (d) ZnS and (e) P25.

To meet a topic highlithed in the literature and related to the diversity of development methods, the synthesis conditions, the nature of the catalysts and the involved dopants, the approach adopted was to elaborate a wide catalyst panel, representative of those tested in previous papers, with a unique synthesis method. Then, in a comparative study, the effectiveness of the elaborated doped nanocatalysts was established by experimental measurements carried out under perfectly controlled irradiation (Figure 16). Efficiency is quantify thanks modeled an effective kinetic constant representative of the amount of photo-degraded molecules divided by the number of photons absorbed. These results show that the efficiencies of the catalysts are low (Figure 17). The main conclusion is that absorbed photons are less effective when their energy content is low, even if high enough to be above the energy gap; the structures of catalysts with low energy gap are supposed to facilitate the recombination process

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Figure 13 : Experimental kinetics of mineralization measurements with the solar simulator associated with different filters..

Figure 14 : Variation of the constant (α) as a function of the band gap energy of the (□) Oxides, (◊) Sulphides, (∆) Alloyed ZnO, (○) Disulfides, (+) Selenide, (Х).

In conclusion, our approach aims at middle term to establish a correlation between the catalyst properties and their performances. Our results show the importance of the synthesis conditions. They focus primarily on the relationship between the performance of the catalyst and its spectral operating range: low energy photons are inefficient. In the visible, improve the efficiency of these catalysts would intensify the process of solar performance very significantly. More generally limit the recombination process (also in the UV range) to produce a more important number of radicals for a given number of photons, is the main breakthrough to perform.

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