A visible light driven photoelectrocatalytic fuel cell for clean-up of contaminated water supplies

A visible light driven photoelectrocatalytic fuel cell for clean-up of contaminated water supplies
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  A visible light driven photoelectrocatalytic fuel cell for clean-up of contaminated water supplies Donald Macphee a  , Richard Wells a , Angela Kruth a , Malcolm Todd  a ,Taha Elmorsi a , Cairns Smith  b , Dubravka Pokrajac c , Norval Strachan d  ,Mwiny Mwinyhija d  , Efe Scott-Emuakpor  d  , Silke Nissen d  , Ken Killham d  a  Department of Chemistry, University of Aberdeen, University of Aberdeen, United KingdomTel. +44 (0)1224 272941; Fax 44 (0)1224 272921; email: d.e.macphee@abdn.ac.uk, r.wells@abdn.ac.uk,a.kruth@abdn.ac.uk, m.j.todd@abdn.ac.uk  b  Department of Public Health, University of Aberdeen, United Kingdomemail: w.c.s.smith@abdn.ac.uk  c  Department of Engineering, University of Aberdeen, United Kingdomemail: d.pokrajac@abdn.ac.uk  d  School of Biological Science, University of Aberdeen, United Kingdomemail: n.strachan@abdn.ac.uk, s.nissen@abdn.ac.uk, k.killham@abdn.ac.uk  Received 31 January 2008; revised accepted 15 May 2008 Abstract A visible light driven photoelectrocatalytic fuel cell (PECFC) recently developed at Aberdeen has been shown to have thecapacitytooxidativelydegradeawiderangeofcontaminantscommonlyfoundinwatersuppliesandassociatedwithrisktohumanhealth. It has also shown great potential to kill human pathogens such as toxigenic strains of   Escherichia coli . Remediation of chemical contaminants has been confirmed by analytical chemistry, and we have integrated a biosensor based assay into the pro-cess to confirm concomitant removal of all chemical toxicity. We have also used a biosensor approach to confirm considerablereduction in infection potential associated with human pathogens. The PECFC used to generate the data comprised a basic, batchsystem with sub-optimal catalyst and static conditions. We are now evaluating the performance of a dynamic, flow reactor (withcatalyst optimisation) which continually delivers water borne contaminants (molecules or cells) to the catalyst surface.  Keywords:  Photoelectrocatalytic fuel cell; PCP; DCP; Biosensor; Pathogens; Toxicity 1. Introduction The World Health Organisation has identified unsafe water, sanitation and hygiene as one of the toptenriskstohealthintermsoftheburdenofdiseasethey  Presented at the Water and Sanitation in International Development and Disaster Relief (WSIDDR) International WorkshopEdinburgh,Scotland,UK,28–30May2008. 0011-9164/0x/$– See front matter  # 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.desal.0000.00.000 Desalination 251 (2010) 132–137  cause [21]. More than 1 billion people in developingcountrieslackaccesstosafewater,around2milliondieannuallyfromdiarrhoealdiseasealonewiththeburdenmainly falling on children. Access to safe water is partof Millennium Development Goal 7 with the target of halving by 2015 the proportion of people without sus-tainable access to safe drinking water and sanitation.Contamination of water involves both chemical (e.g.chlorinated phenolics from industry and agriculture)and biological agents (e.g. human pathogens) and this paper addresses the potential of a visible light driven photoelectrocatalytic fuel cell (PECFC) to remediate both forms of contamination. 2. Background The analysis by the UK Department for Interna-tional Development of the percentage of populationswith access to safe water has identified sub-SaharanAfrica as the region with by far the lowest coverageat50 % ,withthecoverageinruralcommunitiesofonly39 % compared to 77 % in urban areas [9]. The greatestgains can be made by developing and targeting novelinterventions to the areas of lowest coverage.Clorinatedphenolicsrepresentacommonandtoxicform of chemical contamination where industries suchas tanning produce these compounds through bleach-ing and other processes [13,14]. Pentachlorophenol(PCP) and dichlorophenol (DCP) are particularlyimportant in this respect and are difficult to removeusing a number of conventional water treatment tech-nologiesbecause oftheir recalcitranceand strongtoxi-city [10]. The latter can be readily demonstrated usingwhole cell microbial (bacterial) biosensing [6,7,19].Human pathogens, particularly enteric bacteria(e.g. strains of   Escherichia coli ) transmitted throughfaecal contamination, are commonly found to causedisease in drinking water and can persist for consider-able periods of time in water supplies [1] and in soilwhich drains into water supplies [8]. The pathogen isintroduced into the soil environment from animalhosts,andis ofteninitiallypresentatveryhighpopula-tion densities (e.g. 10 7  per gram in cattle faeces, and 10 6  per gram in soil recently exposed to cattle wastes[3,4].Survival insoils prior toleachingintowatersup- plies can be very considerable (several months) [3,4],so that there is intermittent introduction into the drink-ing water (as cells are leached through macropores inthesoil)overlongtimeperiodsandthereisalmostcon-tinual threat to public health [2].A number of researchers have investigated the potential of heterogeneous photocatalysis for degrada-tion of a wide range of organic compounds (e.g.[5,11,12]). Advanced oxidation processes (AOP) suchas photocatalysis offer a valuable alternative to other remediation techniques. As well as being employablefor the treatment of water and wastewater, they aresuitable for the removal of organic and inorganic pol-lutants at low concentrations [15]. In terms of a sus-tainability comparison to conventional technologies(e.g. adsorption to granular activated carbon) thatrelocate the pollutant from an aqueous matrix into asolid matrix, photocatalysis requires no waste post-treatment.Theworkreportedexploresthepotentialofanovel, photoelectrolytic fuel cell (PECFC) technology for remediation of a range of contaminants in water. Wereport the use of immobilised tungsten trioxide (WO 3 )as a catalyst in a photoelectrocatalytic (PEC) batchreactordrivenbyavisiblelightsource.WO 3 hasproventobeanefficientphotocatalystforarangeofchemicals[20], and is also resistant against photocorrosion [17].Furthermore, such working electrodes are suitable for the treatment of aqueous solutions with a low load of organic pollutants. In the configuration reported here,the photocatalytic function of WO 3  is enabled by theelectrochemistry of the reactor, resulting in an  output  of electrical current. To our knowledge, it is the firsttime that a PECFC batch reactor with a WO 3  catalyst,drivenbyvisiblelight,hasbeeninvestigatedtodegradeorgano-xenobiotics, as well as kill human pathogens,and generate an electrical current.The contaminant targets investigated in this paper relate to key, current health threats to the quality of drinking water of developing countries such as Kenya,resulting from both chemical and biological contami-nation. For example, PCP is a common contaminantassociatedwiththetanningindustry,DCPisacommoncontaminant where chlorinated phenolic pesticides areused, and pathogenic strains of   E. coli  are ubiquitouscontaminants where biological active wastes enter water courses.  D. Macphee et al. / Desalination 251 (2010) 132–137   133  3. Materials and methods 3.1. PECFC batch system The PECFC batch system comprised two major compartments connected by a salt bridge (Fig. 1). Thefirst compartment (anode) contained the target con-taminant dissolved in deionised water (70 ml) immer-sing the catalyst (1 cm 2 ) suspended on a conductiveglassslideandtheelectrode[18].Thesecondcompart-ment (cathode) consisted of deionised water throughwhichair was bubbledvia a fishtankpump immersinga platinum mesh. The unit was connected to anammeter and data logger to record photocurrent. 3.2. Assessment of PECFC performance Thebatchcellperformanceintermsofdegradationofthe targetchemicalcontaminantswas carried out byanalyticalchemistry,usingUV/Visspectrophotometryfor the PCP and both UV/Vis spectrophotometry and HPLC (C18reverse phase)for theDCP against knownstandards. In addition, toxicological monitoring wascarriedoutusingaluminescence( lux CDABE)marked  bacterial biosensor (  E. coli  HB101 pUCD607) as pre-viously described bySinclair etal. [19]. The  lux repor-ter genes are downstream of a strong, constitutive cell promoter and so light output is directly proportional tometabolic activity. This means that acute toxicity isassociated with a decline in luminescence.Assessment of PECFC performance in terms of  pathogen attenuation was carried out by using a non-toxigenic, chromosomally  lux  marked   E. coli O157:H7 strain as a cell suspension (10 7 ml  1 ) in the batchcellandmonitoringofluminescenceasareporter ofmetabolicactivitybyluminometryandcolonyform-ing units by agar based plate counting [16]. 4. Results Thedatareportedrepresentproofofconceptresultsin terms of water treatment with the batch PECFC and indicate that the PECFC has considerable potential todegrade PCP, DCP and additional potential to killenteric human pathogens such as toxigenic strains of   E. coli ,withconcomitant removalofallchemical toxi-city(Figs.2and3)andconsiderableinfectionpotential(Fig. 4), respectively.In terms of the chemical contaminants, approxi-mately50 % wasdegradedwithin24hand72hforPCPand DCP, respectively, with a concomitant decline intoxicity.Thiscombineduseofanalyticalchemistryand toxicological testing with the biosensor assay repre-sents a powerful approach for evaluating the potentialof this technology for water sanitation with associated human health consequences, as well as confirming thecompatibility of the technology with other water treat-ment approaches.In terms of the biological contaminants, metabolicactivity (measured by luminescence) of the human pathogen  E. coli  O157 was no longer detectable after a 48 h period of treatment. Furthermore, plate countdata demonstrated there were no longer any culturable pathogenicbacteriaatthistime.ThePECFChadthere-fore rapidly sterilised the water in terms of this model,human pathogenand this iskey for watertreatment for  potability.The PECFC (World InternationalPropertyOrgani-sation; Patent Publication WO 2004/079847 A2) iscurrently being developed for field prototype applica-tionsundera£1.2MDTI-industrycollaboration.Unitsfordemonstrationarecurrentlybeingproducedandthetechnology development benefits from inputs from aninternationalmanufacturingnetworkwhichanticipatesmultiple application scenarios should enable config-urational flexibility to be accommodated to meetuser/environmental needs. Working electrodeCounter electrode Calomelelectrode Air PlatinumWO34% agar in 3M KCl Glass frits Datalogger Visible light 5 cm Working volume: 70 ml Fig. 1. Schematic of the batch PECFC. 134  D. Macphee et al. / Desalination 251 (2010) 132–137   00.511.522.53200250300350400 wavelength (nm)      a      b     s     o     r      b     a     n     c     e UV−visspectrophotometryindicatesrapid degradation Pentachlorophenol (PCP) 96 hrs Control 30 ppm 24 hrs 01020304050600 2 4 6 8 days in cell    L  u  m   i  n  e  s  c  e  n  c  e   (   %   ) Increase in luminescence indicates reduced toxicity OHClClClClCl •common environmental contaminantderived from bleaching operations•strong association with the  paper industry−levels out at ~50% toxicity decreases * Fig. 2. Degradation of PCP by simple, batch PECFC, as characterised by spectrophotometry and toxicity biosensing. Observe degradation by UV−visible spectrophotometry 2,4 dichlorophenol(DCP) Time [hours] 01020304050    C   /   C    0 Time [hours] 01020304050    %    B   i  o   l  u  m   i  n  e  s  c  e  n  c  e  o   f  n  o  n   t  o  x   i  c  n  e  g  a   t   i  v  e  c  o  n   t  r  o   l 010203040506070 Toxicity decreasesLoss of 2,4-DCPdetermined by HPLC 00.511.522.53200220240260280300 wavelength (nm)   a   b  s  o  r   b  a  n  c  e ClOHCl 1 hr73 hrs65 hrs23.5 hrsControl (20 ppm)   Observe degradation by UV−visible spectrophotometry 2,4 dichlorophenol(DCP) a ubiquitous intermediatein the breakdown of many industrial chlorinated  phenolics  present in industrial effluents and water catchments Time [hours] 01020304050    C   /   C    0 Time [hours] 01020304050    %    B   i  o   l  u  m   i  n  e  s  c  e  n  c  e  o   f  n  o  n   t  o  x   i  c  n  e  g  a   t   i  v  e  c  o  n   t  r  o   l 010203040506070 Toxicity decreasesLoss of 2,4-DCPdetermined by HPLC 00.511.522.53200220240260280300 wavelength (nm)   a   b  s  o  r   b  a  n  c  e ClOHCl   ClOHCl 1 hr73 hrs65 hrs23.5 hrsControl (20 ppm)1 hr73 hrs65 hrs23.5 hrsControl (20 ppm)1 hr73 hrs65 hrs23.5 hrsControl (20 ppm) Fig. 3. Degradation of DCP by simple, batch PECFC, as characterised by spectrophotometry and toxicity biosensing,highlighting a reduction on toxicity concomitant with a reduction in DCP concentration.  D. Macphee et al. / Desalination 251 (2010) 132–137   135  5. Conclusions In this paper, the combined use of chemical analy-sis and biological toxicity assessment proved a highlyuseful approach to assess the capacity of a novel, visi- ble light driven PEC batch reactor to degrade the com-mon water pollutants PCP and 2,4-DCP, and identifythe possible appearance of toxic intermediates. Useof a  lux  marked   E. coli  O157 highlighted the further  potential of the PECFC to target human pathogens.Despite the slow degradation rates associated with thesmallactivecatalystsurfaceareaandsub-optimalflowcharacteristics of this trial reactor, promising remedia-tionofthePCPandDCPwasobserved,withsomeevi-denceofreductionsin  E.coli O157populationdensity.This identifies the considerable potential of thisadvanced oxidative process for the remediation of water contaminated with both organo-xenobiotics and  pathogens, despite the relatively low efficiencyobserved using the current electrode configuration.Theauthorshaverecentlydevelopedaflowreactor PECFC with a WO 3  catalyst integrated into a 400 cm 2  Nafion membrane held in a baffled flow cell and illu-minated by a visible light LED array. Initial testingof this flow reactor (using 4l working volume and aflow (re-circulating) rate of 1 L min  1 demonstrated approximately an order of magnitude greater contami-nant (DCP) degradation performance on a mass per unit volume basis over a similar time period (datanot shown), compared to the batch reactor proof of concept results reported in this paper. This further highlights the potential of this technology for water sanitation, and particularly in solar rich developingcountries. Acknowledgments The authors gratefully acknowledge financial sup- port and technical inputs from Yorkshire Water, Sco-toil Services Limited, and OpTIC Technium and agrant from the UK Department of Trade and Industryunder its Micro and Nanotechnology ManufacturingInitiative – Applied Research Programme (1st round).We also would like to thank Dr. Katherine Chadwick and Dr. Julian Dawson for their extremely valuabletechnical support with the chemical analysis. References [1] R.R.E. Artz and K. Killham, Survival of   Escherichiacoli  O157:H7 in private drinking water wells: Theinfluenceofprotozoalgrazingandelevatedcoppercon-centrations, FEMS Lett. Microbiol., 216(1) (2002)117–122.[2] R.R.E. Artz, J.Townend,K. Brown, W. Towers and K.Killham, Soil macropores and compaction control theleaching potential of   Escherichia coli  O157:H7,Environ. Microbiol., 7 (2005) 241–248.[3] L.M. Avery, P.W. Hill, K. Killham and D.L. Jones,  Escherichia coli  O157 survival following the surfaceand sub-surface application of contaminated organicwastetosoil,SoilBiol.Biochem.,36(2004)2101–2103.[4] L.M. Avery, K. Killham and D.L. Jones, Survival of   E.coli O157:H7inorganicwastesdestinedforlandappli-cation, J. Appl. Microbiol., 98(4) (2004) 814–822.[5] A.J. Bard, Photoelectrochemistry, Science, 207 (1980)139–144.[6] Y.Beaton,L.J.Shaw,L.A.Glover,A.A.MehargandK.Killham, Biosensing 2,4-dichlorophenol toxicity dur-ingbiodegradationby  Burkolderia sp.RASCC2insoil,Environ. Sci. Technol., 33 (1999) 4086–4091.[7] E.M. Boyd, K. Killham and A.A. Meharg, Toxicity of mono,diand tri chlorophenols to luxmarkedterrestrial bacteria,  Burkholderia  species RASC C2 Tn 4431 and   Pseudomonas fluorescens , Chemosphere, 43 (2000)157–166.[8] G.R.Campbell,J.Prosser,L.A.GloverandK.Killham,Detection of   Escherichia coli  O157:H7 in soil and water using multiplex PCR, J. Appl. Microbiol., 91(2001) 1–7. Time [hours] 0 10 20 30 40 50    %    C   F   U   /  m   l 020406080100120    %    B   i  o   l  u  m   i  n  e  s  c  e  n  c  e 020406080100120 % CFU/ml % Bioluminescence Fig. 4. Reduction in the population density of chromoso-mally lux marked   E. coli  O157:H7 in a simple, batchPECFC, as determined by counting bioluminescentcolonies on selective agar. 136  D. Macphee et al. / Desalination 251 (2010) 132–137 
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