UV Disinfection of Giardia lamblia Cysts in Water

Department of Civil and Environmental Engineering, Duke University, Durham, North Carolina 27708, USA.
Environmental Science and Technology (Impact Factor: 5.33). 06/2002; 36(11):2519-22. DOI: 10.1021/es0113403
Source: PubMed


The human and animal pathogen Giardia lamblia is a waterborne risk to public health because the cysts are ubiquitous and persistent in water and wastewater, not completely removed by physical-chemical treatment processes, and relatively resistant to chemical disinfection. Given the recently recognized efficacy of UV irradiation against Cryptosporidium parvum oocysts, the inactivation of G. lamblia cysts in buffered saline water at pH 7.3 and room temperature by near monochromatic (254 nm) UV irradiation from low-pressure mercury vapor lamps was determined using a "collimated beam" exposure system. Reduction of G. lamblia infectivity for gerbils was very rapid and extensive, reaching a detection limit of >4 log within a dose of 10 JM-2. The ability of UV-irradiated G. lamblia cysts to repair UV-induced damage following typical drinking water and wastewater doses of 160 and 400 JM(-2) was also investigated using experimental protocols typical for bacterial and eucaryotic DNA repair under both light and dark conditions. The infectivity reduction of G. lamblia cysts at these UV doses remained unchanged after exposure to repair conditions. Therefore, no phenotypic evidence of either light or dark repair of DNA damage caused by LP UV irradiation of cysts was observed at the UV doses tested. We conclude that UV disinfection at practical doses achieves appreciable (much greater than 4 log) inactivation of G. lamblia cysts in water with no evidence of DNA repair leading to infectivity reactivation.

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    • "Other contaminant water micro-organisms could also be incorporated, especially Giardia (Linden, Shin, Faubert, Cairns, & Sobsey, 2002). Giardia is a prevalent and relatively resistant water pollutant that can be treated with UV irradiation (Gibson, Haas, & Rose, 1999; Linden et al., 2002). "
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    ABSTRACT: Ultraviolet (UV) irradiation for potable water is an important alternative to widespread disinfection methods such as chlorine. Failure of UV irradiation to reduce levels of viable contaminants can lead to enduring health effects, with or without fatalities. Here a new risk assessment of failure of UV irradiation for potable water in turbulent flow in a series annular-reactor is presented using the Friday 13th (Fr 13) methodology of Davey and co-workers (Food Control 29(1), 248-254, 2013). The aim was to demonstrate the effects of random changes in UV parameters on plant failure. Failure is defined as unexpected levels of survival of Escherichia coli, a species of faecal bacteria widely used as an indicator for health risk. The assessment is based on a unit-operations model of UV irradiation together with extensive experimental data of Ye (2007). A failure factor (p) is defined in terms of the design reduction and actual reduction in viable E. coli contaminants. UV irradiation is simulated using a refined (Latin Hypercube) Monte Carlo (r- MC) sampling. Illustrative results show 16 % of apparent successful operations, over the long term, can fail to achieve the design reduction in viable E. coli of 10^-4.35 due to random effects. The analysis is shown to be an advance on current risk assessments because it produces all possible practical UV outcomes. Implications of Fr 13 methodology for practical re-design and targeted physical changes to UV plant for improved reliability and safety is discussed.
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    • "The kinetics of E. coli inactivation is usually described by Chick-Watson first order equation, and it uses the data obtained from plate counts, where accurate enumeration is of high importance to assess microbiological water quality [2]. However, many pathogens like Giardia [3] and Cryptosporidium [4] are resistant to the disinfection doses currently applied for drinking water. Moreover, an additional protection to microorganisms can be attained by their attachment to the biofilms [5]. "

    Full-text · Article · Sep 2014
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    • "Ultraviolet (UV) treatment is often used today in wastewater treatment plants to disinfect effluents before their discharge into receiving waters or for different reclamation purposes (Linden et al. 2003; Locas et al. 2008) because of its effectiveness in inactivating a broad range of pathogens without the formation of harmful by-products (Velez-Colmenares et al. 2011). UVexposure can induce damage to the nucleic acids of a microorganism (Hijnen et al. 2006), as well as some other lethal or sublethal changes in other essential components (proteins, lipids, and membrane; Velez-Colmenares et al. 2011). "
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    ABSTRACT: Photoreactivation is considered to be one of the principal disadvantages of the application of ultraviolet disinfection, but knowledge about the photoreactivation potential is limited since few studies to model photoreactivation have been carried out. In order to develop a model for the prediction of the photoreactivation potential, the photoreactivation of Escherichia coli, fecal coliforms, and total coliforms in the tertiary effluent of a wastewater treatment plant was investigated using traditional plate count methods in this study. The tested bacteria were exposed to various UV doses (5–80 mJ/cm2) with a low-pressure UV-collimated beam apparatus and then put under sunlight lamp to experience photoreactivation for up to 72 h. All tested bacteria underwent photoreactivation with a similar trend. When the UV dose increased from 5 to 20 mJ/cm2, the maximum reactivation value of E. coli decreased from 105 to 10 CFU/mL over 8 h, and the reactivation rate decreased from 3.6 to 3.0 × 10−4/h. Based on the photoreactivation results, an exponential model was developed to predict the possible maximum photoreactivation level (N m = αD − β N 0). This simple photoreactivation potential prediction model contains only two variables (UV dose and initial bacterial count), with two constants related to the microorganism species. This model can be easily generalized and is helpful for the optimum design of UV disinfection systems.
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