ARTICLE IN PRESS WAT E R R E S E A R C H 42 2008 483 491 Available at www sciencedirect com journal homepage www elsevier com locate watres Chlorine disinfection of grey water for reuse Effect of organics and particles Gideon P Winwarda Lisa M Averyb Tom Stephensona Bruce Jeffersona a Centre for Water Sciences Building 39 Cranfield University Bedfordshire MK43 0AL UK Catchment Management Macaulay Institute Macaulay Drive Craigiebuckler Aberdeen AB15 8QH UK b art i cle info ab st rac t Article history Adequate disinfection of grey water prior to reuse is important to prevent the potential Received 12 June 2007 transmission of disease causing microorganisms Chlorine is a widely utilised disinfectant Received in revised form and as such is a leading contender for disinfection of grey water intended for reuse This 20 July 2007 study examined the impact of organics and particles on chlorine disinfection of grey water Accepted 24 July 2007 measured by total coliform inactivation The efficacy of disinfection was most closely Available online 31 July 2007 linked with particle size Larger particles shielded total coliforms from inactivation and Keywords Chlorine Disinfection Organics Particles Coliform Grey water 1 disinfection efficacy decreased with increasing particle size Blending to extract particleassociated coliforms PACs following chlorine disinfection revealed that up to 91 of total coliforms in chlorinated grey water were particle associated The organic concentration of grey water affected chlorine demand but did not influence the disinfection resistance of total coliforms when a free chlorine residual was maintained Implications for urban water reuse are discussed and it is recommended that greywater treatment systems target suspended solids removal to ensure removal of PACs prior to disinfection Introduction Grey water is defined as all flows exiting an urban building excluding toilet water Grey water can be considered a suitable candidate for reuse because it is consistently produced and is available onsite for reuse Applications for the reuse of grey water include toilet flushing and garden irrigation Grey water can be further classified as low load and high load in terms of organic strength Low load grey water excludes the more polluted kitchen and laundry wastewater Friedler 2004 Treatment of grey water can range from simple coarse filtration March et al 2004 to advanced biological treatment Nolde 2005 Previous studies have suggested that biological processes should be preferred due to the high levels of organics in the water Nolde 1999 Jefferson et al 2004 Biological greywater treatment technology options for greywater reuse include membrane bioreactor Jefferson et al 2000 rotating biological contactor Nolde 2007 Elsevier Ltd All rights reserved 1999 Friedler et al 2005 or constructed wetland Dallas and Ho 2005 All these biological systems have been capable of meeting a 10 mg L 1 biological oxygen demand BOD standard The major difference between technologies has been the level of suspended solids and microorganism removal In comparison direct physical processes are common at very small scale and have been shown to remove solids but are less effective for organics removal Jefferson et al 2004 Ramon et al 2004 Suspended solids or particles in low load grey water originate from particulate matter shed from the human body hygiene products or sloughed biofilm from collection pipework and are therefore expected to be predominantly organic in composition The mechanisms by which microorganisms become associated with particles in grey water is not understood however microorganisms on the surface of the human body may be shed along with skin material during washing forming a particle with associated microorganisms The Corresponding author Tel 44 1234 754813 fax 44 1234 751671 E mail addresses g p winward cranfield ac uk G P Winward l avery macaulay ac uk L M Avery t stephenson cranfield ac uk T Stephenson b jefferson cranfield ac uk B Jefferson 0043 1354 see front matter 2007 Elsevier Ltd All rights reserved doi 10 1016 j watres 2007 07 042 ARTICLE IN PRESS 484 WA T E R R E S E A R C H sloughing of biofilm formed in greywater collection pipework is another potential source of particle associated microorganisms Indicator bacteria coliforms Escherichia coli and enterococci are consistently detected in grey water Ottoson and Stenstro m 2003 demonstrating the potential for a range of enteric pathogenic bacteria e g Salmonella Campylobacter protozoa e g Cryptosporidium Giardia and viruses e g rotavirus norovirus to persist in grey water Indeed previous studies have isolated the opportunistic pathogens Pseudomonas aeruginosa and Legionella pneumophilia from grey water Casanova et al 2001 Birks et al 2004 Microbiological standards or guidelines for urban water reuse vary worldwide The California State Title 22 guidelines state that total coliforms should not exceed 2 2 CFU 100 mL 1 as an average over a 7 day period The USEPA guidelines specify that faecal coliforms and viable pathogens should be non detectable in water intended for urban reuse The presence of pathogens in grey water and their potential transmission via reuse applications as well as the existence of water quality standards dictate that effective disinfection of grey water prior to reuse is essential Coliform bacteria are useful as indicators providing a measure of disinfection efficacy however their suitability as indicators for the disinfection of specific pathogens particularly viruses and protozoa is questionable The importance of investigating the inactivation of coliform bacteria as a measure of disinfection success is stipulated by their inclusion in water reuse standards Chlorine is a widely utilised disinfectant and as such is a leading candidate for disinfection of grey water intended for reuse The precise mechanism of microorganism inactivation by chlorine has not been fully elucidated Studies have shown however that the bacterial cell membrane undergoes changes in permeability in the presence of chlorine and that the membrane is an important factor in determining bacterial resistance to chlorine disinfection Venkobachar et al 1977 Virto et al 2005 Existing knowledge about the application of chlorine in associated fields has shown that suspended solids or particles and organics in wastewater are able to provide protection to microorganisms Organic content in wastewater creates chlorine demand reducing the
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