Nigel Graham

Imperial College London, Londinium, England, United Kingdom

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Publications (164)413.1 Total impact

  • Source
    Wenzheng Yu · John Gregory · Nigel Graham
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    ABSTRACT: Hydrous oxides of Al(III) and Fe(III) play a large part in environmental processes and in the action of coagulants used in water and wastewater treatment. Aggregates (flocs) of hydroxide precipitates can be rather weak and are easily broken by applied shear. It is usually found that broken flocs do not fully regrow under low shear conditions and this could be a serious disadvantage in practical applications. The irreversible nature of floc breakage suggests that some form of specific, chemical interaction between precipitate particles must be at least partly responsible. Based on experiments reported here and elsewhere, we propose that hydroxyl bridges between particles play a part. When these are broken, there is a reduction in the number of 'active' surface groups that are able to form new bridges. When small amounts of fluoride are added during breakage of Al flocs, there can be significant improvement in floc regrowth, although this depends on a number of factors, especially pH. With Fe flocs, fluoride has no noticeable effect. These results can be explained by the formation of soluble Al-F complexes and some dissolution of the Al(OH)3 precipitate. This creates new surface with more 'active' groups that can form new hydroxyl bridges.
    Full-text · Article · Jan 2016 · Environmental Science & Technology
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    ABSTRACT: The degradation kinetics of three pesticides - metaldehyde, clopyralid and mecoprop - by ultraviolet photolysis and hydroxyl radical oxidation by low pressure ultraviolet hydrogen peroxide (LP-UV/H2O2) advanced oxidation was determined. Mecoprop was susceptible to both LP-UV photolysis and hydroxyl radical oxidation, and exhibited the fastest degradation kinetics, achieving 99.6% (2.4-log) degradation with a UV fluence of 800 mJ/cm2 and 5 mg/L hydrogen peroxide. Metaldehyde was poorly degraded by LP-UV photolysis while 97.7% (1.6-log) degradation was achieved with LP-UV/H2O2 treatment at the maximum tested UV fluence of 1000 mJ/cm2 and 15 mg/L hydrogen peroxide. Clopyralid was hardly susceptible to LP-UV photolysis and exhibited the lowest degradation by LP-UV/H2O2 among the three pesticides. The second-order reaction rate constants for the reactions between the pesticides and OH-radicals were calculated applying a kinetic model for LP-UV/H2O2 treatment to be 3.6x108, 2.0x108 and 1.1x109M-1 s-1 for metaldehyde, clopyralid and mecoprop, respectively. The main LP-UV photolysis reaction product from mecoprop was 2-(4-hydroxy-2-methylphenoxy) propanoic acid, while photo-oxidation by LP-UV/H2O2 treatment formed several oxidation products. The photo-oxidation of clopyralid involved either hydroxylation or dechlorination of the ring, while metaldehyde underwent hydroxylation and produced acetic acid as a major end product. Based on the findings, degradation pathways for the three pesticides by LP-UV/H2O2 treatment were proposed.
    No preview · Article · Jan 2016 · Water Research
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    Hooman Armand · Ivan Stoianov · Nigel Graham
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    ABSTRACT: Cost-effective management of leakage has driven the sectorization of water supply networks into discrete areas that are referred to as District Metered Areas (DMAs). The resulting change in network topology has a major impact on the hydrodynamic conditions and consequently changes in water quality. This paper investigates the impact of DMAs on the potential for discoloration by analysing the spatio-temporal distribution of historic discoloration-related customer contacts for a UK water company. The results demonstrate that the sectorization of networks could have a negative effect on discolouration. A management strategy to reduce the risk of discoloration in DMA-based systems is discussed.
    Preview · Article · Dec 2015 · Procedia Engineering
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    ABSTRACT: This study examined the formation of selected disinfection byproducts (DBPs) during the chlorination of breakfast, Earl Grey and green tea, and from instant and filter coffee. Eight model compounds representing the organics in tea and coffee were also tested. Initially, experiments using water pre-spiked with chlorine demonstrated chlorine concentrations of 1–19 mg L−1 were reduced by 5–19% through boiling in a kettle. The chloroform (trichloromethane) yield of 47.6 ± 0.3% from chlorination of catechin hydrate is high compared with surrogates of drinking water natural organic matter (NOM). Chloroform yields from tea chlorinated under formation potential conditions were similar to reactive drinking water NOM isolates and higher than from coffee. Chloroform generated during the preparation of tea reached 30–43 μg L−1 at the highest chlorine dose of 14.2 mg L−1. Under the same conditions no chloroform was detected in instant coffee, whereas up to 3 μg L−1 chloroform was generated from filter coffee. Overall, this study demonstrates the potential for DBP formation when tea is prepared in water containing elevated chlorine concentrations, such as following point-of-use treatment. Conversely, chloroform concentrations in tea prepared with water containing 1 mg L−1 chlorine were ≤4 μg L−1 and therefore trichloromethane (THM) concentrations in tea made using municipal tap water are likely to be insignificant.
    Full-text · Article · Nov 2015
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    Wenzheng Yu · Lei Xu · Nigel Graham · Jiuhui Qu

    Full-text · Dataset · Nov 2015
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    Wenzheng Yu · Nigel J.D. Graham
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    ABSTRACT: The accumulation of residual coagulant flocs and microbial substances on the surface of ultrafiltration (UF) membranes are major contributors to membrane fouling that reduces process performance. Previous approaches to reduce fouling (e.g. addition of an oxidant or disinfectant) have been only partly successful in reducing the formation of a cake layer and material deposits within membrane pores. In this study the performance of an integrated granular media – UF membrane process has been evaluated in which a hollow-fibre UF module was embedded within a sand layer in order to prevent fouling material reaching the UF surface (forming a cake layer). The evaluation involved comparing two laboratory-scale UF systems, operated in parallel for 74 days, with one incorporating the sand layer (CSUF, coagulation-sand layer filtration-ultrafiltration), and the other without (CUF, coagulation-ultrafiltration), serving as a reference conventional process. The results showed that the incorporation of the sand layer successfully prevented the formation of any significant cake layer on the membrane surface and substantially reduced inner membrane fouling, which lead to a much reduced trans-membrane pressure (TMP) increasing rate. The difference in performance was principally attributed to microbial growth and the release of extracellular polymeric substances (EPS) which was much greater in the conventional CUF system. Thus, in the CUF system, the deposition of coagulation flocs (consisting of precipitated nano-scale primary particles) and bacteria on, and within, the membrane produced substantial reversible and irreversible fouling. In contrast, the deposited material (flocs) in the sand layer of the CSUF system was easy to be washed away, resulting in fewer bacteria in the sand layer, and a much reduced production of biopolymer and other EPS, and their accumulation by the UF membrane.
    Full-text · Article · Oct 2015 · Journal of Membrane Science
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    Wenzheng Yu · Lei Xu · Nigel Graham · Jiuhui Qu
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    ABSTRACT: A coagulation (FeCl3)-ultrafiltration process was used to treat two different raw waters with/without the presence of Fe3O4 nanoparticle contaminants. The existence of Fe3O4 nanoparticles in the raw water was found to increase both irreversible and reversible membrane fouling. The trans-membrane pressure (TMP) increase was similar in the early stages of the membrane runs for both raw waters, while it increased rapidly after about 15 days in the raw water with Fe3O4 nanoparticles, suggesting the involvement of biological effects. Enhanced microbial activity with the presence of Fe3O4 nanoparticles was evident from the measured concentrations of extracellular polymeric substances (EPS) and deoxyribonucleic acid (DNA), and fluorescence intensities. It is speculated that Fe3O4 nanoparticles accumulated in the cake layer and increased bacterial growth. Associated with the bacterial growth is the production of EPS which enhances the bonding with, and between, the coagulant flocs; EPS together with smaller sizes of the nano-scale primary particles of the Fe3O4-CUF cake layer, led to the formation of a lower porosity, more resilient cake layer and membrane pore blockage.
    Full-text · Article · Aug 2015 · Scientific Reports
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    ABSTRACT: Despite the recent focus on nitrogenous disinfection byproducts in drinking water, there is limited occurrence data available for many species. This paper analyses the occurrence of seven haloacetonitriles, three haloacetamides, eight halonitromethanes and cyanogen chloride in 20 English drinking water supply systems. It is the first survey of its type to compare bromine substitution factors (BSFs) between the haloacetamides and haloacetonitriles. Concentrations of the dihalogenated haloacetonitriles and haloacetamides were well correlated. Although median concentrations of these two groups were lower in chloraminated than chlorinated surface waters, median BSFs for both in chloraminated samples were approximately double those in chlorinated samples, which is significant because of the higher reported toxicity of the brominated species. Furthermore, median BSFs were moderately higher for the dihalogenated haloacetamides than for the haloacetonitriles. This indicates that, while the dihalogenated haloacetamides were primarily generated from hydrolysis of the corresponding haloacetonitriles, secondary formation pathways also contributed. Median halonitromethane concentrations were remarkably unchanging for the different types of disinfectants and source waters: 0.1 μg·mgTOC(-1) in all cases. Cyanogen chloride only occurred in a limited number of samples, yet when present its concentrations were higher than the other N-DBPs. Concentrations of cyanogen chloride and the sum of the halonitromethanes were not correlated with any other DBPs. Copyright © 2015 Elsevier Ltd. All rights reserved.
    No preview · Article · Aug 2015 · Water Research
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    ABSTRACT: This paper concerns a previously unreported mechanism of membrane ultrafiltration (UF) fouling when a UF process with coagulation pre-treatment is used in drinking water treatment. The significance of settled coagulant solids (sludge) with different age within the membrane tank on UF fouling has been investigated at laboratory-scale, using model micro-polluted surface water. The process of floc crystallization and increasing bacterial EPS with solids (sludge) retention time may be detrimental to UF operation by causing an increased rate of membrane fouling. In this study the performance of two alum pre-treated hollow-fibre UF units, operated in parallel but with different settled sludge retention times (1 and 7 days), was compared. The results showed that over 34 days of operation the extent of reversible and irreversible fouling was much greater for the 7-day solids retention time. This was attributed to the greater extent of bacterial activity and the presence of Al-nanoparticles, arising from sludge crystallization, at the longer retention time. In particular, greater quantities of organic matter, particularly EPS (proteins and polysaccharides), were found in the UF cake layer and pores for the 7-day retention time. The addition of chlorine later in the membrane run substantially reduced the rate of membrane fouling for both sludge retention times, and this corresponded to reduced quantities of organic substances, including EPS, in the cake layer and pores of both membranes. The results suggest that bacterial activity (and EPS production) is more important than the production of Al-nanoparticles from solids crystallization in causing membrane fouling. However, it is likely that both phenomena are interactive and possibly synergistic. Copyright © 2015 Elsevier Ltd. All rights reserved.
    No preview · Article · Jul 2015 · Water Research
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    L.J. Xu · W. Chu · Nigel Graham
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    ABSTRACT: The influence of physicochemical properties on the sonolytic and sonophotolytic degradation of a group of short-chain phthalate acid esters (PAEs) was investigated in this study. A 400 kHz ultrasonic system and a photolytic system at 253.7 nm were employed separately and together, and both pure water and secondary effluent were used as the water matrices. It was found that PAEs with greater hydrophobicity demonstrated more rapid sonolysis and exhibited greater competitiveness in sonochemical reactions in the presence of other compounds. However, although a greater compound hydrophobicity is beneficial for the sonochemical degradation of PAEs, the observed synergy between ultrasound and UV in the sonophotolytic process is reduced owing to the lower accumulation of H2O2 in the aqueous phase. For the sonophotolysis of PAEs in secondary effluent, it was found that PAEs with greater hydrophobicity experienced less inhibition or competition from the background organic substances (expressed as TOC). Identification of prominent degradation intermediates of di-n-butyl phthalate (DBP), as a representative PAE, indicated that hydroxylation of the aromatic ring and butyl-scission of the aliphatic chain are the principal degradation mechanisms. The combined process of US/UV produced a greater degree of DBP mineralization than either US or UV alone (17% TOC reduction within 90 min).
    Full-text · Article · May 2015 · Journal of Hazardous Materials
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    Dataset: NaClO
    Wenzheng Yu · Lei Xu · Nigel Graham · Jiuhui Qu

    Full-text · Dataset · May 2015
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    Wenzheng Yu · Luiza Campos · Tong Shi · Guibai Li · Nigel Graham
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    ABSTRACT: High levels of manganese (Mn) are known to occur in ground waters and some organic-rich surface waters, and are sometimes in a form (e.g. organically-bound) that is difficult to remove during conventional drinking water treatment. In this study the potential benefits of combining permanganate and chlorine prior to coagulation for Mn removal have been investigated, with particular reference to an organic-rich surface water (river Bajiang, China). The respective roles and potential synergy of permanganate and chlorine when applied together were considered by comparing the removal of Mn with the chemicals together and separately, using samples of river water and model organic-Mn solutions (humic acid and EDTA). In addition, the significance of the order of NaClO and KMnO4 dosing, and the influence of coagulant dose have been evaluated. The results have shown that the combination of the two chemicals is beneficial and synergistic. For river water containing 0.22 mg/L Mn, a dose of 1.76 mg/L NaClO reduced half dose of the permanganate required to achieve the drinking water target concentration of 0.05 mg/L Mn. The addition of chlorine appears to enhance the release of bound-Mn and the subsequent conversion of Mn(II) to insoluble Mn(IV). The mechanisms responsible are believed to involve chlorine-assisted autocatalytic Mn oxidation and MnO4- recycling.
    Full-text · Article · Mar 2015 · RSC Advances
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    Wenzheng Yu · John Gregory · Luiza C. Campos · Nigel Graham
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    ABSTRACT: Kaolin suspensions were coagulated with AlCl3 and a high-basicity PACl at pH 7, at dosages that gave zeta potentials close to zero. The actions of the two coagulants were completely different. With AlCl3, the formation of an amorphous hydroxide precipitate played a dominant role. When the coagulant was added to the suspension, flocs grew rapidly and incorporated most of the kaolin particles within the hydroxide precipitate. When the suspension was added some time after the coagulant, the clay particles were found to be mainly on the outer floc surfaces, although the floc size was about the same. The light scattering properties of the flocs were very dependent on the number and location of particles in the precipitate. With PACl, delaying the addition of kaolin had no influence on the final floc properties. In further tests, different suspensions over a range of concentrations were coagulated with alum at pH 7. Monitoring by a ‘turbidity fluctuation’ technique showed an apparent increase in floc size with increasing particle concentration. However, floc sizes determined from microscope images were very nearly constant, independent of particle nature and concentration. With different particle types, the monitoring results were greatly dependent on the light scattering properties of the particles. Particles incorporated within hydroxide flocs appeared to have no influence on floc properties, such as size and strength.
    Full-text · Article · Mar 2015 · Water Research
  • Zhijun Ren · Nigel Graham
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    ABSTRACT: This article summarizes a preliminary investigation of the treatment of humic acid (HA) in drinking water by a novel combination of potassium manganate, ferrous sulfate, and magnetic ion exchange (MIEX) resin. Manganate (MnO42−) is a stronger oxidant than permanganate, which has received little attention to date as a water treatment chemical, but in combination with ferrous sulfate (FeMnO) can offer a potentially advantageous and more economical means of achieving preoxidation objectives and in-situ coagulation by Fe(III) species. To enhance removal of organic substances, particularly low-molecular-weight and more hydrophilic compounds, subsequent treatment by MIEX was included as part of the overall process. Using model HA solutions of 5 mg/L dissolved organic carbon (DOC), a solution pH of 6.5, and a constant Fe:Mn molar ratio (2:1), the optimal FeMnO dose for organics (DOC) removal was 0.06 mM (as K2MnO4). At this optimal dose, and with 10 mL/L of MIEX, the DOC remaining after treatment was only 0.4 mg/L, representing an overall organics removal of 92%. Synchronous fluorescence spectra of solutions during the treatment stages showed a corresponding major reduction in fluorophore peaks with a near complete removal of fluorophore compounds in the ranges, 360 nm<λex<420 nm and λex>420 nm.
    No preview · Article · Mar 2015 · Environmental Engineering Science
  • Source
    Wenzheng Yu · Nigel. J.D. Graham
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    ABSTRACT: This paper describes some results of mini-pilot-scale tests concerning the performance of potassium manganate (K2MnO4) as a pre-treatment chemical prior to ultrafiltration. Manganate is an intermediate in the commercial preparation of permanganate and in aqueous reactions MnO42− can act as both an oxidant and a coagulant/adsorbent arising from the formation of insoluble MnO2. In addition, the combination of ferrous sulfate and manganate (Fe/Mn), offers a potentially cheaper and effective combination of pre-oxidant and coagulant compared to the chemicals used currently in water treatment (e.g. ozone, chlorine, ferric sulfate). In comparative tests with conventional ferric sulfate and using simulated raw water, the results showed that Fe/Mn pre-treatment substantially reduced membrane fouling in terms of the rate of trans-membrane pressure development (arising from both external and internal fouling). Fe/Mn pre-treatment was effective in reducing bacterial activity, changing the characteristics of organic matter and decreasing the production of extracellular polymeric substances (EPS) by bacteria. The external fouling in this process was determined by the EPS concentration, and the internal fouling mainly determined by the adsorption of lower MW organic matter to the membrane pores. Fe/Mn pre-treatment reduced the amounts of both types of fouling material within the cake layer and membrane pores in comparison to conventional pre-treatment with ferrous sulfate, most likely through the formation of solid-phase Fe(III) and MnO2 and by MnO42− oxidation, thereby leading to a substantial increase in membrane run time.
    Full-text · Article · Jan 2015 · Journal of Membrane Science
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    ABSTRACT: Uncertainty regarding changes in dissolved organic carbon (DOC) quantity and quality has created interest in managing peatlands for their ecosystem services such as drinking water provision. The evidence base for such interventions is, however, sometimes contradictory. We performed a laboratory climate manipulation using a factorial design on two dominant peatland vegetation types (Calluna vulgaris and Sphagnum Spp.) and a peat soil collected from a drinking water catchment in Exmoor National Park, UK. Temperature and rainfall were set to represent baseline and future conditions under the UKCP09 2080s high emissions scenario for July and August. DOC leachate then underwent standard water treatment of coagulation/flocculation before chlorination. C. vulgaris leached more DOC than Sphagnum Spp. (7.17 versus 3.00 mg g−1) with higher specific ultraviolet (SUVA) values and a greater sensitivity to climate, leaching more DOC under simulated future conditions. The peat soil leached less DOC (0.37 mg g−1) than the vegetation and was less sensitive to climate. Differences in coagulation removal efficiency between the DOC sources appears to be driven by relative solubilisation of protein-like DOC, observed through the fluorescence peak C/T. Post-coagulation only differences between vegetation types were detected for the regulated disinfection by-products (DBPs), suggesting climate change influence at this scale can be removed via coagulation. Our results suggest current biodiversity restoration programmes to encourage Sphagnum Spp. will result in lower DOC concentrations and SUVA values, particularly with warmer and drier summers.
    No preview · Article · Dec 2014 · Water Research
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    Wenzheng Yu · Lei Xu · Nigel Graham · Jiuhui Qu
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    ABSTRACT: Microbial effects are believed to be a major contributor to membrane fouling in drinking water treatment. Sodium hypochlorite (NaClO) is commonly applied in membrane cleaning, but its potential use as a pretreatment for controlling operational fouling has received little attention. In this study, the effect of adding a continuous low dose of NaClO (1 mg/l as active Cl) in combination with alum, before ultrafiltration, was compared with only alum as pretreatment. The results showed that the addition of NaClO substantially reduced membrane fouling both in terms of the rate of TMP development and the properties of the membrane cake layer. Although the size of nano-scale primary coagulant flocs changed little by the addition of NaClO, the cake layer on the membrane had a greater porosity and a substantially reduced thickness. NaClO was found to inactivate bacteria in the influent flow, which reduced both microbial proliferation and the production of proteins and polysaccharides in the cake layer and contributed significantly to improving the overall ultrafiltration performance. NaClO dosing had no adverse impact on the formation of currently regulated disinfection by-product compounds (THMs and HAAs).
    Full-text · Article · Oct 2014 · Scientific Reports
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    Tom Bond · Michael R Templeton · Omar Rifai · Hussain Ali · Nigel J D Graham
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    ABSTRACT: Ozonation before chlorination is associated with enhanced formation of chloropicrin, a halonitromethane disinfection by-product (DBP), during drinking water treatment. In order to elucidate reasons for this, five natural organic matter (NOM) surrogates were treated using both chlorination and ozonation-chlorination under controlled laboratory conditions. Selected surrogates comprised two phenolic compounds, two free amino acids and one dipeptide; these were resorcinol, 3-aminophenol, L-aspartic acid, β-alanine and ala-ala, respectively. Quantified DBPs included chloropicrin, chloroform, dichloroacetonitrile and trichloroacetonitrile. Relative to chlorination alone, increases in the formation of chloropicrin from ozonation-chlorination varied from 138% for 3-aminophenol to 3740% for ala-ala for the four amine surrogates. This indicates that ozone is more effective than chlorine in mediating a rate-limiting oxidation step in chloropicrin formation, most plausibly involving conversion of an amine group to a nitro group. While both hydrophilic and hydrophobic surrogates acted as chloropicrin precursors, ala-ala was the most reactive precursor following ozonation-chlorination. Since peptides are far commoner in drinking water sources than free amino acids, further research into chemical oxidation of these species by ozone and chlorine is recommended. In contrast, oxidation with ozone prior to chlorination reduced chloroform formation moderately for the two phenolic compounds.
    Full-text · Article · Sep 2014 · Chemosphere
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    ABSTRACT: This paper investigates the impact of the dynamic hydraulic conditions on the kinetics of chlorine decay in water supply systems. A simulation framework has been developed for the scale-adaptive hydraulic and chlorine decay modelling under steady- and unsteady-state flows. An unsteady decay coefficient is defined which depends upon the absolute value of shear stress and the rate of change of shear stress for quasi-unsteady and unsteady-state flows. By coupling novel instrumentation technologies for continuous hydraulic monitoring and water quality sensors for in-pipe water quality sensing a pioneering experimental and analytical investigation was carried out in a water transmission main. The results were used to model monochloramine decay and these demonstrate that the dynamic hydraulic conditions have a significant impact on water quality deterioration. The spatial and temporal resolution of experimental data provides new insights for the near real-time modelling and management of water quality as well as highlighting the uncertainty and challenges of accurately modelling the loss of disinfectant in water supply networks.
    No preview · Article · Jul 2014 · Journal of Hydroinformatics
  • Wenzheng Yu · Lei Xu · Jiuhui Qu · Nigel Graham
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    ABSTRACT: Pre-coagulation by alum before ultrafiltration without (CUF) and with (CAUF) powdered activated carbon (PAC) addition was investigated to explore the influence of PAC on membrane fouling. It was found that the continuous addition of a low dosage of PAC reduced membrane fouling for operational run periods <20 days, both for reversible and for irreversible components of fouling. The presence of PAC increased the removal of dissolved organic matter (DOM), particularly proteinaceous substances, and some fractions of humic-type substances. For a longer operation time (>20 days) an increase in mainly reversible fouling was evident and was attributed to microorganism growth in the cake layer, as indicated by the enhanced concentrations of extracellular polymeric substances, such as polysaccharides and proteins. A process of crystallization of the coagulant floc in the cake layer with increasing operation time was believed to cause desorption of DOM from primary coagulation particles and a decrease in their size, and consequently a higher density of cake layer. PAC absorption of desorbed DOM within the cake layer, and residual DOM after coagulation, reduced DOM reaching the membrane surface and the extent of subsequent internal membrane fouling.
    No preview · Article · Jun 2014 · Journal of Membrane Science

Publication Stats

4k Citations
413.10 Total Impact Points

Institutions

  • 1986-2016
    • Imperial College London
      • Department of Civil and Environmental Engineering
      Londinium, England, United Kingdom
  • 2002-2010
    • The Hong Kong Polytechnic University
      • Research Centre for Environmental Technology & Management
      Hong Kong, Hong Kong
  • 2007
    • King Juan Carlos University
      Madrid, Spain
  • 2005
    • University of Minho
      Bracara Augusta, Braga, Portugal
  • 2001
    • University of London
      Londinium, England, United Kingdom