Chlorine disinfection of grey water for reuse: Effect of organics and particlesIntroductionMaterials and methodsGreywater characteristicsPreparation of glassware and chlorine dosing solutionsChlorine inactivation experimentsParticles and chlorine disinfectionPACs and chlorine contact timeOrganics and chlorine disinfectionResults and discussionGreywater characteristicsChlorine inactivation of indicator bacteria in grey waterImpact of particle size on chlorine disinfectionImpact of organics on chlorine disinfectionImplications for urban reuseConclusionsAcknowledgementsReferencesAvailable at www.sciencedirect.comjournal homepage: www.elsevier.com/locate/watresChlorine disinfection of grey water for reuse: Effect oforganics and particlesGideon P. Winwarda, Lisa M. Averyb, Tom Stephensona, Bruce Jeffersona,aCentre for Water Sciences, Building 39, Cranfield University, Bedfordshire MK43 0AL, UKbCatchment Management, Macaulay Institute, Macaulay Drive, Craigiebuckler, Aberdeen AB15 8QH, UKarticle infoArticle history:Received 12 June 2007Received in revised form20 July 2007Accepted 24 July 2007Available online 31 July 2007Keywords:ChlorineDisinfectionOrganicsParticlesColiformGrey waterabstractAdequate disinfection of grey water prior to reuse is important to prevent the potentialtransmission of disease-causing microorganisms. Chlorine is a widely utilised disinfectantand as such is a leading contender for disinfection of grey water intended for reuse. Thisstudy examined the impact of organics and particles on chlorine disinfection of grey water,measured by total coliform inactivation. The efficacy of disinfection was most closelylinked with particle size. Larger particles shielded total coliforms from inactivation anddisinfection efficacy decreased with increasing particle size. Blending to extract particle-associated coliforms (PACs) following chlorine disinfection revealed that up to 91% of totalcoliforms in chlorinated grey water were particle associated. The organic concentration ofgrey water affected chlorine demand but did not influence the disinfection resistance oftotal coliforms when a free chlorine residual was maintained. Implications for urban waterreuse are discussed and it is recommended that greywater treatment systems targetsuspended solids removal to ensure removal of PACs prior to disinfection.& 2007 Elsevier Ltd. All rights reserved.1. IntroductionGrey water is defined as all flows exiting an urban building,excluding toilet water. Grey water can be considered asuitable candidate for reuse because it is consistentlyproduced and is available onsite for reuse. Applications forthe reuse of grey water include toilet flushing and gardenirrigation. Grey water can be further classified as low load andhigh load in terms of organic strength. Low-load grey waterexcludes the more polluted kitchen and laundry wastewater(Friedler, 2004). Treatment of grey water can range fromsimple coarse filtration (March et al., 2004) to advancedbiological treatment (Nolde, 2005). Previous studies havesuggested that biological processes should be preferred dueto the high levels of organics in the water (Nolde, 1999;Jefferson et al., 2004). Biological greywater treatment technol-ogy options for greywater reuse include membrane bioreactor(Jefferson et al., 2000), rotating biological contactor (Nolde,1999; Friedler et al., 2005) or constructed wetland (Dallas andHo, 2005). All these biological systems have been capable ofmeeting a 10 mg L1biological oxygen demand (BOD) stan-dard. The major difference between technologies has beenthe level of suspended solids and microorganism removal. Incomparison, direct physical processes are common at verysmall scale and have been shown to remove solids but are lesseffective for organics removal (Jefferson et al., 2004; Ramonet al., 2004).Suspended solids, or particles, in low-load grey wateroriginate from particulate matter shed from the human body,hygiene products or sloughed biofilm from collection pipe-work, and are therefore expected to be predominantly organicin composition. The mechanisms by which microorganismsbecome associated with particles in grey water is not under-stood; however, microorganisms on the surface of the humanbody may be shed along with skin material during washing,forming a particle with associated microorganisms. TheARTICLE IN PRESS0043-1354/$ - see front matter & 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.watres.2007.07.042Corresponding 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) 483– 491sloughing of biofilm, formed in greywater collection pipe-work, is another potential source of particle-associatedmicroorganisms.Indicator bacteria (coliforms, Escherichia coli and enterococ-ci) are consistently detected in grey water (Ottoson andStenstro¨m, 2003), demonstrating the potential for a range ofenteric pathogenic bacteria (e.g. Salmonella, Campylobacter),protozoa (e.g. Cryptosporidium, Giardia) and viruses (e.g.rotavirus, norovirus) to persist in grey water. Indeed, previousstudies have isolated the opportunistic pathogens Pseudomo-nas aeruginosa and Legionella pneumophilia from grey water(Casanova et al., 2001; Birks et al., 2004). Microbiologicalstandards or guidelines for urban water reuse vary worldwide.The California State Title 22 guidelines state that totalcoliforms should not exceed 2.2 CFU100 mL1as an averageover a 7-day period. The USEPA guidelines specify that faecalcoliforms and viable pathogens should be non-detectable inwater intended for urban reuse. The presence of pathogens ingrey water and their potential transmission via reuseapplications, as well as the existence of water qualitystandards, dictate that effective disinfection of grey waterprior to reuse is essential. Coliform bacteria are useful asindicators, providing a measure of disinfection efficacy;however, their suitability as indicators for the disinfectionof specific pathogens, particularly viruses and protozoa, isquestionable. The importance of investigating the inactiva-tion of coliform bacteria as a measure of disinfection successis stipulated by their inclusion in water reuse standards.Chlorine is a widely utilised disinfectant, and as such is aleading candidate for disinfection of grey water intended forreuse. The
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