2003 Progress Report: Effectiveness of UV Irradiation for Pathogen Inactivation in Surface Waters

EPA Grant Number: R829012
Title: Effectiveness of UV Irradiation for Pathogen Inactivation in Surface Waters
Investigators: Linden, Karl G. , Shin, Gwy-Am , Sobsey, Mark D.
Current Investigators: Linden, Karl G. , Sobsey, Mark D.
Institution: Duke University , University of North Carolina at Chapel Hill
EPA Project Officer: Page, Angela
Project Period: August 20, 2001 through August 19, 2004 (Extended to August 19, 2005)
Project Period Covered by this Report: August 20, 2002 through August 19, 2003
Project Amount: $524,848
RFA: Drinking Water (2000) RFA Text |  Recipients Lists
Research Category: Drinking Water , Water


Ultraviolet (UV) irradiation now is recognized to be a cost-effective and relatively convenient means to achieve effective disinfection against many waterborne microorganisms, and it does not appear to produce any significant level of disinfection byproducts at practical doses. However, there are still some important issues that need to be assessed, such as the germicidal effects of UV against emerging pathogens and challenges related to application of UV disinfection for filtered and unfiltered surface waters. The objectives of this research project are to: (1) evaluate the susceptibility and resistance of select Contaminant Candidate List (CCL) pathogens and indicators to UV disinfection from low- and medium-pressure UV sources; and (2) investigate their ability to repair UV-induced damage under conditions typically found in water distribution systems; (3) elucidate the relative germicidal effectiveness of different wavelengths of UV light for these pathogens and indicators; and (4) investigate the extent to which microbes are associated with water treatment particles typical in unfiltered systems and the effects of this particle association and other water quality parameters on UV disinfection potential. It is hypothesized that UV will be an effective means to inactivate CCL pathogens, and that with proper system design, repair/reactivation and water quality challenges found in typical treatment scenarios will not compromise effective UV treatment.

Progress Summary:

Phase I. UV Dose Response for Pathogens

In addition to the work reported in Year 1 of the project, we have performed an inactivation study on adenovirus 41 with a newly developed molecular biology assay (cell culture mRNA reverse transcription-polymerase chain reaction [RT-PCR]). Our results based on the new assay showed that adenovirus 41 is highly resistant to UV radiation—only 3.6 log10 inactivation with a UV dose of 200 mJ/cm2—which is somewhat more resistant than those in a previous study using a conventional cell culture infectivity assay method (Meng and Gerba, 1996). However, a recent study by the same research group (Thurston-Enriquez, et al., 2003) showed that adenovirus 40 is somewhat more resistant to UV irradiation than they originally reported (4 log10 inactivation of adenovirus 40 was achieved with a UV dose of 226 mJ/cm2). We also have performed an inactivation study on the Norwalk virus with a newly developed molecular biology assay (long-template [LT] RT-PCR). Our results showed that the Norwalk virus is extremely resistant to UV radiation—only 1 and 2 log10 inactivation with a UV dose of 150 mJ/cm2 based on the traditional and the new assays, respectively.

Phase II. Wavelength Effectiveness

Because of problems in the collaboration with the Duke University Free Electron Laser Laboratory, we had to set up a method to perform wavelength specific studies using a polychromatic UV light source (medium pressure mercury vapor lamp) and a set of UV bandpass filters. These filters are capable of passing specific wavelength ranges (between 214 and 300 nm) of light from the UV source. This setup has been utilized to develop wavelength effectiveness information for coliphage MS2, bacteriophage PRD-1, and Escherichia coli. However, this setup has some problems with resolution of the bandwidth being wider than we would have liked. Thus, we are in the process of obtaining a light source that can create a narrower bandwidth to perform the remainder of the studies. In the meantime, we collaborated with the University of Vienna, School of Veterinary Medicine, Institute for Medical Physics (Dipl.-Ing Alexander Cabaj), and performed the wavelength dependent inactivation studies on two strains of Bacilus subtilis spores and MS2 coliphage. This work also was conducted with the assistance of Professor Regina Sommer at the University of Vienna, Institute for Hygiene and Medical Microbiology.

Phase III. Pathogen Clumping and Particle Association

Following the studies on dose response of indigenous aerobic spores, we proceeded to isolate four environmental strains. We examined the UV dose response for these strains, and found that they were much more susceptible to UV after culturing compared to the precultured strain. These findings led to some investigations on the physical state of the spores, including hydrophobicity, surface charge, and particle size. Also of interest were the differences noted in the shoulder portions of the inactivation curve and the tailing portion of these curves. Studies are now focused on the effects of different coagulation conditions typically used in water treatment relating to the state of aggregation of the spores. These flocculated microbes will be evaluated for zeta potential, as well as hydrophobicity, surface charge, and particle size. We have found some interesting correlations with these physical properties of the individual spores and the aggregation of spores with particles. This work is being supplemented by some interesting microscopy work using scanning confocal and scanning electron microscopy to evaluate the state of aggregation of the spores with which we are working.

In addition to the spore work, we have developed methods to prepare various cell-associated adenoviruses and coxsackieviruses. Three different states of cell-associated viruses are being used to determine the effect of cell association on UV disinfection against adenoviruses and coxsackieviruses.

Phase IV. Repair/Recovery of UV-Irradiated Pathogens

We have finished setting up DNA repair systems for both light and dark repair to determine the presence and extent of repair and recovery following UV irradiation. These systems have been verified with E. coli. We will implement these systems to evaluate the presence and extent of repair of UV-irradiated Mycobacterium spp. and Toxoplasma gondii oocysts under the conditions typically found in clearwells, distribution systems, and aqueducts. Along with these repair systems, we also have established a molecular biology assay (endonuclease sensitive site [ESS] assay) to better quantify the extent of DNA repair in the UV-irradiated microorganisms. We have verified this assay system with E. coli, and will employ this assay on the repair studies on UV-irradiated Mycobacterium spp. and T. gondii oocysts.

Phase V. Development of Multibarrier Disinfectant Approaches Using UV and Chlorine

We have set up a sequential disinfection system with UV irradiation and chlorine species (free chlorine and chloramines). In addition to the UV disinfection units, we have constructed a bench-scale chemical disinfection unit that consists of a plastic tank, recirculating water bath, and a magnetic stirrer. With this sequential disinfection system, we have performed inactivation studies on several microorganisms including adenovirus 2. Our results showed that, contrary to its response to UV irradiation, adenovirus 2 is highly sensitive to free chlorine, so that a significant inactivation (> 4 log10) of this adenovirus can be achieved by practical doses and contact time of UV irradiation and free chlorine. We will use this sequential disinfection setup to evaluate the inactivation of other adenoviruses (adenoviruses 40 and 41), Mycobacterium spp., T. gondii oocysts, and some other test micro-organisms proposed.

Future Activities:

We will complete the wavelength effectiveness studies for adenovirus 2 and the Norwalk virus in the near future. Following the study on the effect of cell association on UV disinfection against adenoviruses and coxsackieviruses, we will start the study on the effect of particle association on UV disinfection against the Norwalk virus. Work with Mycobacteria will commence in water to examine the effect of aggregation of this microbe on disinfection. The coagulation studies with the spores will continue. We also will continue evaluating the repair and recovery of UV-irradiated Mycobacterium spp. and T. gondii oocysts using both infectivity and the newly employed molecular biology assay (ESS assay). Finally, the focus will be on sequential disinfection studies for the inactivation of various pathogens.

Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 25 publications 12 publications in selected types All 12 journal articles
Type Citation Project Document Sources
Journal Article Ko G, Cromeans TL, Sobsey MD. UV inactivation of adenovirus type 41 measured by cell culture mRNA RT-PCR. Water Research 2005;39(15):3643-3649. R829012 (2003)
R829012 (Final)
  • Abstract from PubMed
  • Full-text: Science Direct Full Text
  • Other: Science Direct PDF
  • Journal Article Mamane-Gravetz H, Linden KG. UV disinfection of indigenous aerobic spores: implications for UV reactor validation in unfiltered waters. Water Research 2004;38(12):2898-2906. R829012 (2003)
    R829012 (2004)
    R829012 (Final)
  • Abstract from PubMed
  • Full-text: Science Direct Full Text
  • Other: Science Direct PDF
  • Journal Article Shin G-A, Linden KG, Sobsey MD. Low pressure ultraviolet inactivation of pathogenic enteric viruses and bacteriophages. Journal of Environmental Engineering and Science 2005;4(S1):S7-S11. R829012 (2003)
    R829012 (Final)
  • Abstract: NRC Research Press Abstract
  • Supplemental Keywords:

    ultraviolet, UV, environmental engineering, UV inactivation, action spectra, aggregation, Contaminant Candidate List, CCL, pathogens, risk management, Giardia, UV treatment, chlorination, chlorine-based disinfection, contaminant candidate list, cryptosporidium, parvum oocysts, disinfection byproducts, DBPs, dosimetry, drinking water system, drinking water contaminants, drinking water treatment, exposure, exposure and effects, irradiation, microbial risk management, microbiological organisms, monitoring, public health, treatment, water quality., RFA, Scientific Discipline, Water, Environmental Chemistry, Health Risk Assessment, Ecological Risk Assessment, Ecology and Ecosystems, Drinking Water, Environmental Engineering, cryptosporidium parvum oocysts, pathogens, other - exposure, monitoring, CCL, chlorination, microbiological organisms, exposure and effects, disinfection byproducts (DPBs), exposure, UV treatment, Other - risk management, chlorine-based disinfection, cryptosporidium , public health, treatment, microbial risk management, water quality, DBP risk management, drinking water contaminants, drinking water treatment, Giardia, water treatment, contaminant candidate list, drinking water system, dosimetry

    Relevant Websites:

    http://www.cee.duke.edu/faculty/linden/index.php Exit

    Progress and Final Reports:

    Original Abstract
    2002 Progress Report
    2004 Progress Report
    Final Report