Essential oils for the disinfection of grey waterIntroductionMaterials and methodsWater sample collectionWater quality analysisGrey water manipulationEssential oilsToxicity screening of EOsEssential oil disinfectionUV disinfectionRegrowth experiments with UV and EOsResults and discussionToxicity screeningInactivation curvesImpact of organics on EO disinfectionImpact of particle size on EO disinfectionEOs as regrowth inhibitorsPractical implications for urban water reuseConclusionsAcknowledgementsReferencesAvailable at www.sciencedirect.comjournal homepage: www.elsevier.com/locate/watresEssential oils for the disinfection of grey waterGideon P. Winwarda, Lisa M. Averyb, Tom Stephensona, Bruce Jeffersona,aCentre for Water Sciences, Cranfield University, Building 39, Bedfordshire MK43 0AL, UKbMacaulay Institute, Macaulay Drive, Craigiebuckler, Aberdeen AB15 8QH, UKarticle infoArticle history:Received 7 October 2007Received in revised form28 November 2007Accepted 6 December 2007Available online 15 December 2007Keywords:Grey waterEssential oilOreganoWater reuseRegrowthColiformabstractAlthough the antimicrobial properties of many plant essential oils (EOs) are well known,their application for the disinfection of water has received little attention. In this study,their use as alternative ‘natural’ disinfectants for grey water reuse was assessed. Toxicityscreening of eight EOs and their components highlighted origanum oil (Thymus capitatus)and carvacrol as exerting the most antimicrobial activity. Over a 30-min contact time,origanum EO concentrations of up to 94 mg L1had minimal effect on total coliformconcentrations in the grey water while a concentration of 468 mg L1rendered totalcoliforms non-detectable in 100 mL grey water. Coliform inactivation was found to increasewith EO contact time. Organic concentration and particulate size in grey water were shownto reduce the efficacy of disinfection with origanum EO. Origanum EO prevented regrowthof coliform bacteria in reed bed-treated grey water for up to 14 days at a concentration of468 mg L1, with or without prior disinfection by ultraviolet (UV) light. Based on thedisinfection data reported here, the production of sufficient origanum EO for thedisinfection of grey water for reuse with toilet flushing, would require approximately 35times the average land area of a UK household.& 2007 Elsevier Ltd. All rights reserved.1. IntroductionSmall-scale, decentralised reuse of water is increasinglyviewed as a viable way forward for water conservation inthe urban environment (Anderson, 1996; Fane et al., 2002).Small-scale reuse schemes can range from individual house-holds to clusters of homes, such as blocks of flats, orcommercial premises like hotels. Water reuse schemestypically involve treatment and disinfection of the sourcewater prior to reuse for applications such as toilet flushingand irrigation.Grey water can be defined as all wastewater flows exiting abuilding, with the exception of toilet waste (black water).Depending on the quantity or quality of water required forreuse, grey water is frequently limited to the bathroomstreams of hand basin, shower, and bath water, which areless polluted in terms of organics and bacteria (Friedler, 2004;Jefferson et al., 2004). Faecal contamination of grey water andthe reported presence of pathogenic microorganisms (Otto-son and Stenstro¨m, 2003; Birks et al., 2004) dictates thattreatment and disinfection of grey water is important tocontrol the potential health risks emanating from reuseapplications. The type of treatment and disinfection em-ployed can vary according to the desired application andregional standards for water reuse. Treatment options for greywater reuse include coarse filtration (March et al., 2004), directmembrane filtration (Ramon et al., 2004), constructed wetland(Dallas and Ho, 2005), rotating biological contactor (Nolde,1999), and membrane bioreactor (Jefferson et al., 2000).Chlorine is a leading contender for the disinfection of greywater for reuse due to its widespread use for the disinfectionof wastewater and potable water. Drawbacks of chlorinationARTICLE IN PRESS0043-1354/$ - see front matter & 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.watres.2007.12.004Corresponding author. Tel.: +44 1234 754813; fax: +44 1234 751671.E-mail addresses: [email protected] (G.P. Winward), [email protected] (L.M. Avery), [email protected](T. Stephenson), [email protected] (B. Jefferson).WATER RESEARCH 42 (2008) 2260– 2268include the formation of disinfection by-products that cancause adverse health effects (Morris et al., 1992; Nieuwen-huijsen et al., 2000), and limited efficacy in the presence ofparticles and organics (Winward et al., 2007). Alternativedisinfectants that are perceived as being ‘environmentallyfriendly’ would be an attractive option for operators of small-scale water reuse systems. Such alternatives include ultra-violet (UV) light and plant essential oils (EOs).EOs are aromatic liquids extracted from plant material,typically by steam distillation (Sangwan et al., 2001). EOs andtheir components have been shown to possess antibacterial(Hammer et al., 1999; Burt, 2004), antiviral (Edris, 2007),antiparasitic (Anthony et al., 2005), antifungal (Sokovic´and van Griensven, 2006), insecticidal (Isman, 2000), andherbicidal (Tworkoski, 2002) properties. Research into theantimicrobial properties of EOs and their components hasbeen largely directed towards their use as food preservatives.EOs and their components have been shown to inhibitbacterial growth in meat, fish, and vegetable products (Burt,2004). The principal mechanism of bacterial inactivation byEOs is considered to be the disruption of the cell membrane,causing leakage of cell contents and eventual cell lysis(Burt, 2004). This action of certain EOs can be explainedby the presence of phenolic compounds, common in manyEOs, such as carvacrol, thymol, and eugenol, which areknown to cause such disturbance of the cell membrane(Sikkema et al., 1995).The effective use of EOs and their components as inhibitorsof microbial growth in foods points to their potential asresidual regrowth inhibitors in reused water. This studyinvestigates the disinfection potential of EOs for grey waterreuse, including the impact of organics and particles, andtheir application as residual regrowth inhibitors in reed bed-treated grey water following UV disinfection.2. Materials and
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