ARTICLE IN PRESS WAT E R R E S E A R C H 42 2008 1043 1050 Available at www sciencedirect com journal homepage www elsevier com locate watres UV disinfection of RBC treated light greywater effluent Kinetics survival and regrowth of selected microorganisms Yael Gilboa Eran Friedler Faculty of Civil and Environmental Engineering Technion Israel Institute of Technology Haifa 32000 Israel art i cle info ab st rac t Article history The microbial quality of raw greywater was found to be much better than that of municipal Received 11 April 2007 wastewater with 1 6 107 cfu ml 1 heterotrophic plate count HPC and 3 8 104 9 9 103 Received in revised form 3 3 103 and 4 6 100 cfu 100 ml 1 faecal coliforms FC Staphylococcus aureus sp Pseudo 5 August 2007 monas aeruginosa sp and Clostridium perfringes sp respectively Further three viral Accepted 27 September 2007 indicators monitored somatic phage host Escherichia coli CN13 and F RNA phages hosts Available online 4 October 2007 E coli F amp E coli K12 were not present in raw greywater The greywater was treated by an Keywords Greywater Microbial quality UV disinfection Bacteria Coliphages Disinfection kinetics Regrowth RBC followed by sedimentation The treatment removed two orders of magnitude of all bacteria UV disinfection kinetics survival and regrowth of HPC FC P aeruginosa sp and S aureus sp were examined At doses up to 69 mW s cm 2 FC were found to be the most resistant bacteria followed by HPC P aeruginosa sp and S aureus sp inactivation rate coefficients 0 0687 0 113 0 129 and 0 201 cm2 mW 1 s 1 respectively At higher doses 69 439 mW s cm 2 all but HPC which exhibited a tailing curve were completely eliminated Microscopic examination showed that FC self aggregate in the greywater effluent This provides FC an advantage at low doses since the concentration of suspended matter 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 to increasing UV doses 19 439 mW s cm 2 HPC regrowth was proven to be statistically significant in un disinfected effluent and after irradiation with high UV doses 147 and 439 mW s cm 2 At these doses regrowth resulted from growth of UV resistant bacteria due to decreased competition with other bacteria eliminated by the irradiation 2007 Elsevier Ltd All rights reserved 1 Introduction An increasing interest has been given in recent years to onsite reuse of greywater as a method to decrease the overall urban water demand Eriksson et al 2002 Friedler and Galil 2003 This is due to the fact that greywater is less polluted than municipal wastewater About 60 70 of the domestic water demand is transformed into greywater while the rest is transformed to blackwater wastewater originating from toilets Nevertheless greywater may contain various pollutants such as suspended solids organic matter nutrients and Corresponding author Tel 972 4 8292633 fax 972 4 8228898 E mail address eranf tx technion ac il E Friedler 0043 1354 see front matter 2007 Elsevier Ltd All rights reserved doi 10 1016 j watres 2007 09 027 detergents with turbidity of 15 240 NTU COD of 180 650 mg l 1 5 15 mg l 1 TKN and TP and 1 30 mg l 1 anionic detergents as MBAS Rose et al 1991 ChristovaBoal 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 indicated by up to 107 cfu 100 ml 1 faecal coliforms FC and 105 107 cfu ml 1 heterotrophic plate count HPC may present a public health hazard with respect to reuse Since pathogens distribution in greywater may not reflect that in domestic wastewater FC which is commonly used as ARTICLE IN PRESS 1044 WAT E R R E S E A R C H 42 2008 1043 1050 indicator of pathogens concentration in wastewater may be insufficient to fully characterise its microbial quality and the associated health risk Avery 2005 Ottoson and Stenstrom 2003 Greywater due to its origin may contain skin and mucous tissues pathogens such as Pseudomonas aeruginosa sp and Staphylococcus aureus sp which were found in greywater at concentrations of 2 4 102 and 5 105 cfu 100 ml 1 respectively 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 as 106 107 cfu 100 ml 1 Friedler et al 2006 Furthermore greywater originating from the kitchen sink and dishwasher may contain pathogens introduced by food handling such as Salmonella sp Burrows et al 1991 Rose et al 1991 Viruses comprise a serious risk to health due to their relatively low infection dose Dixon et al 1999 The concentration of viruses found in greywater depends on the health of the population generating the water with rising probability to find virus in the greywater as the contributing population increases From the above it is obvious that only after appropriate treatment greywater can be reused for garden irrigation and toilet flushing Attention should be given to the sanitary quality of greywater especially when on site reuse is considered due to the relatively close proximity between the reused greywater and the general public Birks et al 2004 Friedler et al 2006 When greywater is reused for toilet flushing the health risk is associated with splashing when the toilet is used and with aerosols that may form when the toilet is flushed and thus with possible inhalation or ingestion of small droplets of greywater Christova Boal et al 1996 Avery 2005 When greywater is reused in garden irrigation the health risk is associated mainly with body contact and splashing UV irradiation is considered to be an advanced disinfection method which is gaining popularity It has a number of advantages over chlorination which makes it especially suitable for small scale treatment plants There is no need for storage of the disinfector which itself may be hazardous there is no need for dosing apparatus which is quite costly it does not create unwanted by products and it effectively removes a wide range of pathogens USEPA 2003 Ijpelaar et al 2005 Much attention was given in the literature to UV disinfection of potable water and municipal wastewater or wastewater effluent on the other hand much less attention has been paid to UV disinfection of greywater effluent Fenner and Komvuschara 2005 This paper investigates the kinetics of UV disinfection of greywater as a possible post treatment of greywater effluent
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