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Abstract: In recent years, there has been a tremendous amount of research and development in the area of photocatalysis (heterogeneous and homogeneous), a process included in a special class of oxidation techniques defined as Advanced Oxidation Processes (AOPs), all characterized by the same chemical feature, production of ls. This paper reviews the use of sunlight to produce the ls by TiO2 photocatalysis and photo-Fenton process. The reacting systems necessary for performing solar photocatalysis are described. The paper also summarizes most of the research carried out related to solar photocatalytic degradation of water contaminants, and how it could significantly contribute to the treatment of persistent toxic compounds. It outlines how to enhance the process efficiency by integration with biotreatment. Various solar reactors for photocatalytic water treatment mainly based on non-concentrating collectors built during the last few years are also described in detail in this review, as well as the use of the solar photocatalytic processes to inactivate microorganisms present in water, placing special emphasis on experimental systems made to optimize this disinfection technique. [Copyright &y& Elsevier]

A new granulated version of the well-known P-25 titanium dioxide (VP AEROPERL® P-25/20 (Aeroperl)) has been tested to determine whether its photocatalytic efficiency is good enough for use in photocatalytic water purification and to find out if it can be separated from water more easily than its well-known homologue, powdered Degussa P-25, a significant technical improvement that might eliminate the tedious final filtration necessary with a slurry. Furthermore, a new commercial catalyst (PC-100 from Millennium Inorganic Chemicals), having a surface area and structure that are both different from Degussa P-25, has also been studied. All the experiments were carried out in sunlight in the pilot compound parabolic collector (CPC) plant at the Plataforma Solar de Almerı´a. Three different substrates were chosen as model molecules for this study: dichloracetic acid, phenol and the pesticide imidacloprid. Results show that Degussa Aeroperl is not a good alternative to powdered Degussa P-25 because of its spontaneous sedimentation during photocatalysis. Millennium PC-100 efficiency seems to be in the same range as that of Degussa P-25. In this work we also attempt to demonstrate that the comparison of efficiencies of different photocatalysts is not a trivial matter. Many factors are involved and interfere in the testing of photocatalyst behaviour during the degradation of a contaminant. A thorough comparison of photocatalyst activity should include reactions with several different substrates under varied experimental conditions. [Copyright &y& Elsevier]

The technical feasibility and performance of photocatalytic degradation of four water-soluble pesticides (diuron, imidacloprid, formetanate and methomyl) have been studied at pilot scale in two well-defined systems of special interest because natural-solar UV light can be used: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. The pilot plant is made up of compound parabolic collectors (CPCs) specially designed for solar photocatalytic applications. Experimental conditions allowed disappearance of pesticide and degree of mineralisation achieved in the two photocatalytic systems to be compared. In order to assure that the photocatalytic results are consistent, hydrolysis and photolysis tests have been performed with the four pesticides. The initial concentration tested with imidacloprid, formetanate and methomyl was 50 and 30 mg/l with diuron, and the catalyst concentrations were 200 mg/l and 0.05 mM with TiO2 and iron, respectively. Total disappearance of the parent compounds and 90% mineralisation have been attained with all pesticides tested, methomyl being the most difficult to be degraded with both treatments. First-order rate constants, initial rate, time necessary for mineralising 90% of the initial TOC and hydrogen peroxide consumption were calculated in all cases, enabling comparison both of treatments and of the selected pesticide reactivity. [Copyright &y& Elsevier]

Examines the degradation of imidacloripid in water by photo-fenton and titanium dioxide photocatalysis at a solar pilot plant. Sources of pesticide water pollution; Kinetics and mineralization of imidacloprid; Percentage of mineralization following photocatalytic treatment.

Interest has grown in the modification of titanium dioxide with graphene to improve the photocatalytic behaviour. In this work, titanium dioxide–reduced graphene oxide (TiO 2 –RGO) composites were synthesised by the photocatalytic reduction of exfoliated graphene oxide (GO) by TiO 2 (Evonik P25) under UV irradiation in the presence of methanol as a hole acceptor. The composite materials were characterised using high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Raman and XPS analysis provided evidence that GO was converted to RGO by photocatalytic reduction. The TiO 2 –RGO composites were compared to TiO 2 in suspension reactors for the disinfection of water contaminated with Escherichia coli and Fusarium solani spores under real sunlight. Very rapid water disinfection was observed with both E. coli and F. solani spores. An enhancement in the rate of inactivation of E. coli was observed with the TiO 2 –RGO composite compared to P25 alone. The rate of inactivation of F. solani spores was similar for both the TiO 2 –RGO and P25. When the major part of the solar UVA was cut-off ( λ > 380 nm) using a methacrylate screen, there was a marked increase in the time required for inactivation of E. coli with P25 but no change in the inactivation rate for the TiO 2 –RGO. There is evidence of singlet oxygen production with visible light excitation of the TiO 2 –RGO composites which would lead to E. coli inactivation. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiO 2 -rGO at the solar assisted photodegradation of complex mixing of pesticides. • Best photocatalytic performances with oxygen, regardless of the water matrix. • H 2 O 2 has not improved the final photocatalytic efficiency in any case. • P25-rGO promoted the photo-oxidation of the complex pesticides mix studied. • HBK-rGO presented excellent solar photoefficiency with 200 μg L-1 of pesticides. New titania-reduced graphene oxide (TiO 2 -rGO) nanocomposites have been studied to assess their application in the solar assisted photodegradation of a complex mixing of pesticides (pyrimethanil, isoproturon, alachlor and methomyl) at solar pilot plant, opening the opportunity to extend the use of these hybrid photocatalysts to complex wastewater effluents. TiO 2 -rGO nanocomposites were prepared by hydrothermal method from two commercial TiO 2 , Hombikat UV-100 (HBK) and Aeroxide® P25 (P25). The effect of two different water matrices (simulated and natural) on TiO 2 -rGO solar photoefficiency with two pesticides concentrations (5 mg·L−1 and 200 μg·L−1), and the additional use of an electron scavenging as oxidant agent, such as hydrogen peroxide in a comparison with oxygen from air, has been studied in compound parabolic collectors (CPC) photoreactors. Best photocatalytic performances were always found with oxygen over both TiO 2 -rGO nanocomposites, regardless of the water matrix employed. The use of H 2 O 2 as oxidant agent has not improved the final photocatalytic efficiency in any case. The generation of secondary highly reactive species in the reaction media from reaction of SO 4 ●- /HO radicals, and the more negatively surface charge with low S BET of P25-rGO nanocomposite, besides its lower hydrodynamic size with lower particle aggregation in the reaction conditions, have been responsible to promote the photo-oxidation of the complex pesticides mix studied. Finally, HBK TiO 2 -reduced graphene oxide (HBK-rGO) nanocomposite has presented excellent solar photoefficiency in the photodegradation of 200 μg·L−1 of each pesticide with the oxygen form air, especially under natural water matrix, because of its large negatively charge surface area where probably recombination of electrons and holes is prevented. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to propose a municipal wastewater treatment method based on solar Advanced Oxidation Processes (AOPs) permitting reuse of the treated wastewater. Experiments were performed in a pilot compound parabolic collector (CPC) solar plant at the Plataforma Solar de Almería. Mineralisation was monitored by measuring the dissolved organic carbon (DOC), and the concentration profile of each compound during degradation was determined by HPLC–UV. Two different approaches, photo-Fenton (pH=2.8) and TiO2 were tested with 9 different emerging contaminants at 100μgL−1 each (acetaminophen, antipyrine, atrazine, caffeine, diclofenac, isoproturon, progesterone, sulfamethoxazole, and triclosan) at low iron and TiO2 concentrations. Photo-Fenton was by far more effective than TiO2 for degrading these contaminants, and was therefore selected for further study. The 9 contaminants were tested under the following conditions without pH adjustment: (i) Fe=5mgL−1, D.I. water; (ii) Fe=5, 15 and 55mgL−1, standard fresh water; (iii) Fe=5mgL−1, standard fresh water without NaHCO3. Initial amount of hydrogen peroxide was 50mgL−1, frequently analysed and added to maintain this concentration. It was demonstrated that low efficiency in some cases is mainly due to bicarbonates, and it is therefore proposed that the process be improved, either by increasing the iron concentration, or eliminating bicarbonates. [Copyright &y& Elsevier]

Olive mill wastewater (OMW), a highly polluted wastewater from the olive oil industry, was treated by solar photocatalysis and solar photo-Fenton. Among the tested systems the application of titanium dioxide alone was not successful. The addition of peroxydisulphate as an electron acceptor had only limited effect on degradation performance and led to high salt concentrations (30 g/l sulphate generated) and a pH value near zero. The photo-Fenton method successfully removed up to 85% COD and up to 100% of phenol index of OMW with different initial concentrations and from different sources. Two solar photocatalytic pilot-plant reactors were used; one of conventional CPC type and an open non-concentrating Falling Film Reactor. The latter, newly designed reactor worked properly and yielded comparable results to the CPC in terms of degradation rate referred to incident UV radiation energy per solution volume. The suspended solids in the OMW hinder light from entering the reactor. Therefore, flocculation induced by a commercial flocculation agent was successfully applied to remove suspended solids. Application of this pre-treatment led to considerable increase of degradation rates and decrease of hydrogen peroxide consumption. [Copyright &y& Elsevier]

The photocatalytic organic content reduction of a selected synthetic municipal wastewater by the use of heterogeneous and homogeneous photocatalytic methods under solar irradiation has been studied at a pilot-plant scale at the Plataforma Solar de Almeria. In the case of heterogeneous photocatalysis the effect of catalysts and oxidants concentration on the decomposition degree of the wastewater was examined. By an accumulation energy of 50 kJ L−1 the synergetic effect of 0.2 g L−1 TiO2 P-25 with hydrogen peroxide (H2O2) and Na2S2O8 leads to a 55% and 73% reduction of the initial organic carbon content, respectively. The photo-fenton process appears to be more efficient for this type of wastewater in comparison to the TiO2/oxidant system. An accumulation energy of 20 kJ L−1 leads to 80% reduction of the organic content. The presence of oxalate in the Fe3+/H2O2 system leads to an additional improvement of the photocatalytic efficiency. [Copyright &y& Elsevier]

TiO2-catalyst suspensions work efficiently in photocatalysis for wastewater treatment. Nevertheless, once photocatalysis is complete, separation of the catalyst from solution becomes the main problem. Catalyst recovery has been enhanced through charge neutralisation and coagulation with electrolytes at lab and pilot-plant scale (40 L) to evaluate the potential for its separation after photocatalytic degradation of pollutants. Zeta-potential analysis showed that the isoelectric point (IEP) of TiO2 suspensions is near pH 7. Settling rates and hydrodynamic diameter of TiO2 particles are maximum at the IEP. However, suspensions are stable at different pH. TiO2 was reused in solar photocatalysis pilot-plant (40 L) for treatment of tetrachloroethylene (C2Cl4) comparing two procedures: reuse of the entire suspension after destruction of the organics without separation of the catalyst, and reuse of the catalyst after it had settled to the bottom and clear water had been removed. Photocatalytic efficiency worsens with successive runs when catalyst and water are reused without separation, whereas, when TiO2 is separated, the photocatalyst is not deactivated. [Copyright &y& Elsevier]

The main goal of the present study was to explore pilot-scale combination of H 2 generation with simultaneous water disinfection or decontamination. Performance of a TiO 2 –CuO mixture for solar-to-hydrogen (STH) conversion was studied, focusing on treatment optimization (catalyst dose, proportion of semiconductors in the mixture and concentration of the sacrificial agent). Experiments were performed in a 25-L compound parabolic collector (2 m2) solar pilot plant specifically designed for photocatalytic hydrogen generation. The best operating conditions were 100 mg L−1 TiO 2 –CuO (10:1) with 0.075 M glycerol as the sacrificial agent. The best STH conversion attained was 0.9%. 25 mg L−1 imidacloprid was completely degraded (over 99%). The synergetic effect of anoxic conditions, TiO 2 :CuO and solar radiation caused a significant reduction (>5 Log) in concentration of E. coli , used as a model waterborne pathogen, in less than 10 min. • Photocatalytic H 2 generation with water disinfection or decontamination. • Selection of TiO 2 –CuO mixture dose and proportion of semiconductors. • Reduction (>5 Log) in E. coli concentration in less than 10 min. • Solar photocatalytic H 2 generation at pilot scale. [ABSTRACT FROM AUTHOR]

Agricultural wastewater is characterized by high organic matter and traces of organic pollutants. Effluents from the agro-food industry in particular are a potentially high environmental risk which requires appropriate, comprehensive treatment. This study evaluated the treatment of real wastewater from an agro-food processing plant by an Immobilized Biomass Reactor working in batch and continuous operating modes. Organic matter oxidation and the removal of reference organic pollutants were analyzed. Finally, the efficiency of a photocatalytic tertiary treatment with supported TiO 2 for the IBR effluent containing persistent microcontaminants was also studied. After the combined treatment, imazalil and thiabendazole were completely removed and over 90% of acetamiprid had been eliminated, but only with the additional contribution of hydrogen peroxide as an electron acceptor. [ABSTRACT FROM AUTHOR]

Highlights: [•] Immobilized photocatalyst based on TiO2 on glass spheres was successfully applied for ECs removal. [•] Regeneration with H2O2/UV or calcination are the most efficient methods to recover photoactivity. [•] F-, S- and Cl-containing compounds are preferentially adsorbed and easily removed from titania acid sites. [•] Compounds containing amine and amide groups are resistant to the photodegradation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Structure/activity relationships over nanostructured iron-doped titania photocatalysts for solar degradation of phenol. [•] Iron leaching shown to be most relevant for the photoactivity. [•] Results compared in terms of the oxidizing agent, either H2O2 or oxygen from air. [ABSTRACT FROM AUTHOR]

Highlights: [•] Photocatalysis with TiO2 in the laboratory and in a pilot plant scale is compared. [•] The effect of clouds in the solar pilot plant is checked. [•] Initial pollutant removal is very similar in the pilot plant and in the laboratory. [•] TOC removal is faster at the pilot plant than at the laboratory. [•] Differences found in both installations are attributed to the light sources. [ABSTRACT FROM AUTHOR]

Abstract: The appropriate catalyst concentration for industrial wastewater treatment is several hundred milligrams per liter in solar photoreactors. Nonetheless, when the purpose of eliminating emerging contaminants in municipal wastewater treatment plant effluents is for reuse of the water, and they are present at extremely low concentrations, a tertiary treatment with a much lower photocatalyst concentration might be possible. TiO2 concentrations of only tens of mgL−1 were selected to evaluate the influence of catalyst load, initial hydrogen peroxide dose and radiation intensity on the degradation rate of five emerging contaminants (100μgL−1 of ofloxacin, sulfamethoxazole, flumequine, carbamazepine, and 2-hydroxy-biphenyl) spiked in a real municipal wastewater treatment plant effluent. Response surface methodology based on a spherical central composite design was used to optimize the parameters to find the maximal degradation rate. The experiments were carried out using an Evonik P-25 titanium dioxide suspension in a Suntest solar simulator. It has been demonstrated that the use of hydrogen peroxide is highly recommendable for working with TiO2 at low concentrations and high photon flux must be avoided. It has also been demonstrated that too low (less than 40mgL−1) TiO2 concentration is not recommendable. [Copyright &y& Elsevier]

Abstract: The synergism produced between ozone and TiO2 black light photocatalytic oxidation of methanol has been studied following the rate of formaldehyde formation during photocatalytic oxidation, ozonation and photocatalytic ozonation experiments. Methanol was selected as a model compound due to its low reaction rate with molecular ozone and its scavenging character for both, free hydroxyl radicals and trapped holes. TiO2-P25 was used as photocatalyst and black light blue lamps (emitting with a maximum at 365nm) as radiation source. The effect of ozone concentration and pH was evaluated. Absorbed light intensity by the photocatalyst was also determined to calculate the quantum yields of photocatalytic reactions. Three main processes need to be considered during photocatalytic ozonation: direct ozone-methanol reaction, indirect ozone reactions and photocatalytic reactions, which allow calculating the quantum yield of photo-generated oxidizing species. The presence of ozone exerts a positive effect in the reaction rate of oxidizing species formation due to light induced reactions also enhancing the quantum yield from 0.34 to 0.80moleinstein−1 at pH=3 (where indirect ozone reactions are negligible). This parameter increased from 0.29 to 3.27moleinstein−1 at pH=7 likely due to indirect ozone reactions that cannot be disregarded. The positive effect of ozone in the photocatalytic induced reactions has been attributed to the reaction of dissolved ozone and hydrogen peroxide (formed upon methanol direct ozonation) as electron acceptors, thus reducing the recombination process on the catalyst surface to some extent. A simplified economic study is also presented. [Copyright &y& Elsevier]

Abstract: The optimal photocatalyst concentration for industrial wastewater treatment in current photoreactor designs is several hundreds of milligrams per liter. However, the elimination of emerging contaminants (ECs), which are present at extremely low concentrations in waste water treatment plants (WWTP) effluents might be accomplished at much lower catalyst (TiO2) concentrations. One of the main drawbacks of reducing catalyst loading below the optimum is the loss of useful photons which instead are transmitted through the TiO2 suspension without being absorbed by the catalyst. Accordingly, in this work, laboratory and solar pilot-scale experiments were performed with real WWTP effluents to evaluate the kinetics of photocatalytic degradation of 52 emerging contaminants under realistic (ppb) concentrations. The analysis of the samples was accomplished by solid phase extraction (SPE) followed by liquid chromatography–mass spectrometry (LC–MS). In view of the results, low concentrations of TiO2 of the order of tens of milligrams per liter were found to be insufficient for the degradation of the ECs in photoreactors with a short light-path length (29cm). However, it was established that solar reactors of diameters of several hundreds of millimetres could be used for the efficient removal of ECs from WWTP effluents. The results presented show a general methodology for selecting the most efficient reactor diameter on the basis of the desired catalyst concentration. [Copyright &y& Elsevier]

Abstract: Nanostructured iron-doped TiO2 catalysts with anatase structure and two different iron contents (0.7 and 3.5wt.%) have been prepared by a combined sol–gel/microemulsion method and examined with respect to their behaviour for photocatalytic degradation of aqueous phenol with H2O2 under solar light. The activity results are compared with those obtained for similarly prepared undoped systems as well as Degussa P25 reference catalyst and have been complemented with structural/morphological and electronic characterization analyses achieved by XRD, TEM, Raman, S BET, UV–vis DRS and XPS techniques. In contrast to typically observed results, the highest photoactivity is obtained for the catalyst with highest iron loading while that with 0.7% Fe displays lower photoactivity than undoped samples. Such unusual behaviour has been attributed to the contribution of new photoactive iron complexes generated on the surface of the catalyst as a consequence of iron leaching and readsorption processes taking place during the course of phenol photodegradation process. [Copyright &y& Elsevier]

Abstract: This article reports on degradation using TiO2 immobilized on glass spheres of 15 emerging contaminants (ECs) at low concentrations in simulated and real Municipal Wastewater Treatment Plant (MWTP) effluents. A sol containing titanium isopropoxide, commercial P25 and polyethylene glycol (PEG) was prepared, and a layer of the photoactive precursor was immobilized on glass spheres by dip-coating. The raw materials and the xerogels were characterized by N2 adsorption/desorption, XRD and TGA-DTA. The xerogel showed the TiO2 anatase, rutile and brookite crystal phases characteristic of the reference materials. The diffraction pattern showed no modification of the crystal size from incorporation of the PEG. Two different TiO2 anatase crystal sizes were identified, which was attributed to the different TiO2 precursors used in the synthesis route. Degradation of the emerging contaminants (acetaminophen, antipyrine, atrazine, carbamazepine, diclofenac, flumequine, hydroxybiphenyl, ibuprofen, isoproturon, ketorolac, ofloxacin, progesterone, sulfamethoxazole and triclosan), at an initial concentration of 100μgL−1 each was determined by ultra-performance liquid chromatography (UPLC-UV) and mineralization was monitored by measuring the dissolved organic carbon (DOC). The experiments were performed in a pilot compound parabolic collector (CPC) solar plant at the Plataforma Solar of Almeria (Spain). 85% of the compounds were degraded within 120min of illumination time depending on the water. The results show the potential application of this technology as a good alternative to suspension systems for the treatment of polluted water. [Copyright &y& Elsevier]

Abstract: Photocatalytic degradation of phenol, nalidixic acid, mixture of pesticides, and another of emerging contaminants in water was mediated by TiO2 and iron oxide immobilized on functionalized polyvinyl fluoride films (PVFf–TiO2–Fe oxide) in a compound parabolic collector (CPC) solar photoreactor. During degradation, little iron leaching (<0.2mgL−1) was observed. Phenol was efficiently degraded and mineralized at operational pH<5 and nalidixic acid degradation was complete even at pH 7, but mineralization stopped at 35%. Pesticide mixture was slowly degraded (50%) after 150min of irradiation. Degradation of the emergent contaminant mixture was successful for eight compounds and less efficient for six other compounds. The significant reactivity differences between tested compounds were assigned to the differences in structure namely that the presence of complexing or chelating groups enhanced the rates. PVFf–TiO2–Fe oxide photoactivity gradually increased during 20 days of experiments. X-ray photoelectron spectroscopy (XPS) measurements revealed significant changes on the catalyst surface. These analyses confirm that during photocatalysis mediated by PVFf–TiO2–Fe oxide, some iron leaching led to enlargement of the TiO2 surface exposed to light, increasing its synergy with iron oxides and leading to enhanced pollutant degradation. [Copyright &y& Elsevier]

Experiments based on Vibrio fischeri, activated sludge and Pseudomonas putida have been employed to check variation in the biocompatibility of an aqueous solution of a commercial pesticide, along solar photo-oxidative process (TiO2 and Fenton reagent). Activated sludge-based experiments have demonstrated a complete detoxification of the solution, although important toxicity is still detected according to the more sensitive V. fischeri assays. In parallel, the biodegradability of organic matter is strongly enhanced, with BOD5/COD ratio above 0.8. Bioassays run with P. putida have given similar trends, remarking the convenience of using P. putida culture as a reliable and reproducible method for assessing both toxicity and biodegradability, as a substitute to other more time consuming methods. [Copyright &y& Elsevier]

Abstract: The solar light photocatalytic degradation of ethidium bromide (EtBr) in aqueous suspensions has been analyzed over titania-based catalysts. A nanosized titania and an iron-doped TiO2 (with ≈2wt.% of iron content), synthesized within reverse microemulsions, were compared with a commercial Degussa P-25 titania. Structural and/or light handling properties of a different nature arise upon doping the titania with iron. These include favoring a titania crystal phase transformation from anatase to rutile and lowering the band gap energy. Almost total degradation of EtBr upon solar light assisted photodestruction and with significant total organic carbon (TOC) removal can be achieved over the three studied catalysts although the highest mineralization activity is achieved over the P25 titania sample. The results evidence that heterogeneous photocatalysis can be a promising advanced oxidation process to treat diluted EtBr residues typically generated in biomedical and biomolecular laboratories. [Copyright &y& Elsevier]

Abstract: Titanium dioxide photocatalysis (200mg/L) and photo-Fenton were applied to the treatment of several different pesticides considered priority substances (PS) by the European Commission dissolved in water at 50mg/L or at maximum water solubility (alachlor, atrazine, chlorfenvinphos, diuron, isoproturon and pentachlorophenol) alone (20mg/L of iron) and as a mixture (10mg/L of iron). All tests were performed in new twin 75-L compound parabolic collector (CPC) pilot plants driven by solar energy. Total organic carbon (TOC) mineralisation, disappearance of the parent compound and inorganic ion release are discussed as a function of treatment time. Photo-Fenton treatment was found to be shorter than TiO2 and more appropriate for these compounds and mixtures of them. [Copyright &y& Elsevier]

The solar photodegradation of Sevnol, a commercial pesticide, based on carbaryl as active principle, was studied. Experiments have been carried out at laboratory and at pilot plant scale using titanium dioxide as catalyst. Complete dissappearance of carbaryl was achieved, while total mineralisation required longer irradiation. Active sludge respirometry showed significant detoxification of the solution. Finally, results obtained with commercial Sevnol were consistent with those of pure carbaryl, although the reaction was slower. [ABSTRACT FROM AUTHOR]

Titanium dioxide photocatalysis, using 200 mgl−1 of TiO2, and photo-Fenton, using 20 mg l−1 of iron, were applied to the treatment of dimethoate dissolved in water at 50 mg l−1. A heterogeneous photocatalysis test was performed in a 35-l solar pilot plant with Compound Parabolic Collectors (CPCs) under natural illumination. A homogeneous photocatalysis test was performed in a different solar pilot plant with four CPC units and a total volume of 75 l. In this work total disappearance of dimethoate and 90% of mineralization were attained in both solar treatments. Treatment time, hydrogen peroxide consumption and ferric phosphate precipitation during photo-Fenton treatment were discussed. [ABSTRACT FROM AUTHOR]

Abstract: TiO2 solar photocatalysis has been proven to be a degradation process for aqueous organic contaminant leading to total mineralisation of a large number of compounds. Furthermore, the interest in using this technique for water disinfection has grown in the last decade. Recent publications have reported photokilling of bacteria and viruses by TiO2 photocatalysis. Therefore, solar photocatalysis disinfection seems to be a very promising process, which could help to improve public health in rural areas of developing countries. The objective of this work was to assess the feasibility of using TiO2 solar photocatalysis to disinfect water supplies for future applications in developing countries. This article reviews the viability of solar photocatalysis for disinfection in low cost compound parabolic collectors, using sunlight and titanium dioxide semiconductor, both applied as slurry and supported. We report on the bactericidal action of TiO2 on a pure culture of Escherichia coli with a low cost photoreactor based on compound parabolic collectors. The influence of different experimental set-ups and parameters are also analysed. The results and potential application of the solar photocatalysis technology to water disinfection are studied within the frame of two research EU projects whose objective consist on the development of a fully autonomous solar reactor system to purify drinking water in remote locations of developing countries. [Copyright &y& Elsevier]

The technical feasibility and performance of photocatalytic TiO2 coatings in batch-process solar disinfection (SODIS) reactors to improve potability of drinking water in developing countries have been studied. Borosilicate glass and PET plastic SODIS reactors fitted with flexible plastic inserts coated with TiO2 powder were shown to be 20% and 25% more effective, respectively, than standard SODIS reactors for the inactivation of E. coli K12. Isopropanol at 100 ppm concentration levels was observed to be completely photodegraded after 24 h continuous exposure to 100 mW/cm2 simulated sunlight in a similar solar photocatalytic disinfector (SPC-DIS) reactor. The technique for producing the TiO2-coated plastic inserts is described and demonstrated to be an appropriate and affordable technology for developing countries. [Copyright &y& Elsevier]

The technical feasibility and performance of photocatalytic degradation of aqueous methomyl (50 mg/L) have been studied at pilot scale in two well-defined systems of special interest because natural-solar UV light can be used: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. The pilot plant is made up of compound parabolic collectors specially designed for solar photocatalytic applications. Experimental conditions allowed pesticide disappearance, degree of mineralisation and toxicity achieved in the two photocatalytic systems to be compared. Total disappearance of methomyl is attained by photo-Fenton in 60 min and by TiO2 in 100 min. Hundred percent of nitrogen and sulphur are recovered as ammonium and sulphate. By contrast, complete mineralisation of total organic carbon (TOC) is not achieved even after quite a long time (more than 300 min). Three different bioassays (Vibrio fischeri, Daphnia magna and a Microalga) have been used for testing the progress of toxicity during treatment. All remained toxic down to very low-pesticide concentrations and in some bioassays were still toxic after total disappearance of the pesticide. Only if treatment is maintained throughout enough mineralisation (i.e. TOC disappearance), the toxicity is reduced to below the threshold (EC50%). [Copyright &y& Elsevier]

Describes the solar photocatalytic detoxification of non-biodegradable chlorinated hydrocarbon solvents in different concentrating and non-concentrating devices. Use of titanium dioxide as a photocatalyst fixed on the inner surface of the reaction tubes or as a slurry catalyst which has to be removed from the treated water; Glass quality; Degradation tests.

The photocatalytic oxidation of 2,4-dichlorophenol (DCP), using TiO{sub}2{end} suspensions under solar radiation, has been studied at pilot-plant scale at the Plataforma Solar de Almeria (PSA). Two different reactor designs were tested: a medium concentrating radiation system called a Parabolic-Trough-Collector Reactor, PTCR, equipped with two motors (azimuth and elevation) to adjust the position of the moduleperpendicular to the sun, and a low-concentrating radiation system, the Compound-Parabolic-Concentrator Reactor, CPCR, facing South and inclined 37 degrees. Substrates were dissolved in water to required mgL{sup}-1{end} levels in a reservoir tank. In both cases, 0.2 g L{sup}-1{end} of the suspended TiO{sub}2{end} catalyst was used in a 250 Lsolution of the contaminant, which was recirculated through the photoreactors using a centrifugal pump and an intermediate reservoir tank. The advantages and disadvantages of the two types of photoreactors in DCP oxidation are compared and discussed. The strong potential of photocatalytic peroxydisulphate-assisted degradation in high DCP Concentrations was demonstrated in both systems, and chemical actinometry(the decomposition reaction of oxalic acid by radiated uranyl salts)in the CPC reactor is compared with the results obtained in the PTC. [ABSTRACT FROM AUTHOR]