UV disinfection of RBC-treated light greywater effluent: Kinetics, survival and regrowth of selected microorganismsIntroductionMethodsDescription of the pilot plantBacterial and viral indicatorsAnalysis methodsUV disinfectionResults and discussionMicrobial quality of raw greywater and effluentDisinfection kineticsRegrowthConclusionsAcknowledgementsReferencesAvailable at www.sciencedirect.comjournal homepage: www.elsevier.com/locate/watresUV disinfection of RBC-treated light greywater effluent:Kinetics, survival and regrowth of selected microorganismsYael Gilboa, Eran FriedlerFaculty of Civil and Environmental Engineering, Technion—Israel Institute of Technology, Haifa 32000, Israelarticle infoArticle history:Received 11 April 2007Received in revised form5 August 2007Accepted 27 September 2007Available online 4 October 2007Keywords:GreywaterMicrobial qualityUV disinfectionBacteriaColiphagesDisinfection kineticsRegrowthabstractThe microbial quality of raw greywater was found to be much better than that of municipalwastewater, with 1.6 107cfu ml 1heterotrophic plate count (HPC), and 3.8 104, 9.9 103,3.3 103and 4.6 100cfu 100 ml 1faecal coliforms (FC), Staphylococcus aureus sp., Pseudo-monas aeruginosa sp. and Clostridium perfringes sp., respectively. Further, three viralindicators monitored (somatic phage, host: Escherichia coli CN13and F-RNA phages, hosts:E. coli F+amp, E. coli K12) were not present in raw greywater. The greywater was treated by anRBC followed by sedimentation. The treatment removed two orders of magnitude of allbacteria. UV disinfection kinetics, survival and regrowth of HPC, FC, P. aeruginosa sp. andS. aureus sp. were examined. At doses up to 69 mW s cm 2FC were found to be the mostresistant bacteria, followed by HPC, P. aeruginosa sp. and S. aureus sp. (inactivation ratecoefficients: 0.0687, 0.113, 0.129 and 0.201 cm2mW 1s 1, respectively). At higher doses(69–439 mW s cm 2) all but HPC (which exhibited a tailing curve) were completelyeliminated. Microscopic examination showed that FC self-aggregate in the greywatereffluent. This provides FC an advantage at low doses, since the concentration of suspendedmatter (that can provide shelter from UV radiation) in the effluent was very low. FC,P. aeruginosa sp. and S. aureus sp. did not exhibit regrowth up to 6 h after exposure toincreasing UV doses (19–439 mW s cm 2). HPC regrowth was proven to be statisticallysignificant in un-disinfected effluent and after irradiation with high UV doses (147 and439 mW s cm 2). At these doses regrowth resulted from growth of UV-resistant bacteria dueto decreased competition with other bacteria eliminated by the irradiation.& 2007 Elsevier Ltd. All rights reserved.1. IntroductionAn increasing interest has been given in recent years to on-site reuse of greywater as a method to decrease the overallurban water demand (Eriksson et al., 2002; Friedler and Galil,2003). This is due to the fact that greywater is less pollutedthan municipal wastewater. About 60–70% of the domesticwater demand is transformed into greywater, while the rest istransformed to blackwater (wastewater originating fromtoilets). Nevertheless, greywater may contain various pollu-tants such as suspended solids, organic matter, nutrients anddetergents, with turbidity of 15–240 NTU, COD of180–650 mg l 1, 5–15 mg l 1TKN and TP, and 1–30 mg l 1anionic detergents (as MBAS) (Rose et al., 1991; Christova-Boal et al., 1996; Almeida et al., 1999; Dixon et al., 1999;Surandren and Wheatley, 2003; Friedler, 2004; Friedler et al.,2005). Presence of microbial agents in greywater, as indicatedby up to 107cfu 100 ml 1faecal coliforms (FC) and105–107cfu ml 1heterotrophic plate count (HPC), may presenta public health hazard with respect to reuse.Since pathogens distribution in greywater may not reflectthat in domestic wastewater, FC which is commonly used asARTICLE IN PRESS0043-1354/$ - see front matter & 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.watres.2007.09.027Corresponding author. Tel.: +972 4 8292633; fax: +972 4 8228898.E-mail address: [email protected] (E. Friedler).WATER RESEARCH 42 (2008) 1043– 1050indicator of pathogens concentration in waste w ater, may beinsufficient to fully characterise its microbial quality and theassociated health risk (Avery, 2005; Ottoson and Stenstrom,2003). Greywater due to its origin may contain skin and mucoustissues pathogens, such as Pseudomonas aeruginosa sp. andStaphylococcus aureus sp., which were found in greywater atconcentrations of 2–4 102and 5 105cfu 100 ml 1,respec-tivel y (Burrows et al., 1991; Nolde, 1999; Casanova et al., 2001).Faecal contamination, which is measured by FC concentration,exhibits high variability ranging from about 0 to as much as106–107cfu 100 ml 1(Friedler et al., 2006). Furthermore, grey-water originating from the kitchen sink and dishwasher maycontain pathogens introduced by food handling such asSalmonella sp. (Burrows et al., 1991; Rose et al., 1991). Virusescomprise a serious risk to health due to their relatively lowinfection dose (Dixon et al., 1999). The concentration of virusesfound in greywater depends on the health of the populationgenerating the water, with rising probability to find virus in thegreywater as the contributing population increases.From the above, it is obvious that only after appropriatetreatment gre ywater can be reused for garden irrigation andtoilet flushing. Attention should be given to the sanitary qualityof greywater, especially when on-site reuse is considered due tothe relatively close proximity between the reused greyw aterand the general public (Birks et al., 2004; Friedler et al., 2006).When greywater is reused for toilet flushing, the health risk isassociated with splashing when the toilet is used and withaerosols that may form when the toilet is flushed and thus withpossible inhalation or ingestion of small droplets of greywater(Christova-Boal et al., 1996; Av ery, 2005). When greywater isreused in garden irrigation, the health risk is associated mainlywith body contact and splashing.UV irradiation is considered to be an advanced disinfectionmethod, which is gaining popularity. It has a number ofadvantages over chlorination, which makes it especiallysuitable for small-scale treatment plants. There is no needfor storage of the disinfector (which itself may be hazardous);there is no need for dosing apparatus (which is quite costly); itdoes not create
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