Cryptosporidium Control in Drinking Water with UV Disinfection – Status, Experience, Development and Outlook
The following is a review of the workshop co-organized by the IUVA and WRc PLC, held on September 15, 2008 at Imperial College, London. The subject of Cryptosporidium control in drinking water with UV disinfection – status, experience, development and outlook was discussed. Presentations included trends, applications, guidelines and aspects related to regulatory issues from North American and European perspectives.
The workshop was attended by participants from the USA, Canada and Europe, coinciding with recent amendments to UK legislation, allowing for the use of UV as part of Cryptosporidium control. At the workshop, emphasis was placed on the growth of UV use, supported by the presentation of studies indicating that low UV dose rates are required for inactivation of Cryptosporidium.
These findings promoted and continue to promote the conduction of studies in this area, helping UV technology to establish its position as an integral part of the multi barrier system (MBS) in water treatment. The following summary presents the highlights of the lectures presented.
The lecture on UV-Disinfection of drinking water: Opportunities and Limits1 presented a review of UV disinfection capabilities, while emphasizing its relevance in the UK context as a result of recent amendments to the water supply regulations for England and Wales.
These amendments allow water suppliers to control Cryptosporidium using UV, in addition to traditional physical removal that has been applied to date. During the presentation, a graph was presented which displayed the UV dose range required for four-log inactivation. The graph shows that a UV dose of 40 mJ/cm2 is sufficient to inactivate most of the microorganisms presented, with the exception of Adenovirus, which requires a significantly higher UV dose of approximately 120 mJ/cm2 (Figure 1).
Next, a comparison was given between the disinfection capabilities of chlorine and those of UV, during which the benefits of UV usage were presented; when UV is used, there is no formation of trihalomethanes that may be created during the alternative chlorine disinfection process. In addition, the UV dose required for inactivation of Cryptosporidium is low while chlorine has been shown to be ineffective for inactivation of Cryptosporidum. However, the limitations of UV were also presented; UV cannot control taste and odor, nor remove color on its own. Unlike chlorine, UV has no residual disinfecting capabilities.
In addition to the issues of DBPs and operational aspects, a comparison was presented between chlorine and UV with regard to their inactivation capabilities. According to this comparison, when considering the three types of microorganisms (protozoa, bacteria and viruses) it appears that chlorine requires its lowest dose to inactivate bacteria, whereas UV requires the lowest dose to inactivate protozoa (Figure 2).
The presentation continued with a review of the various existing guidelines throughout the world. Included were the German DVGW) standards, Austrian OMORM standards, NSF 55, US EPA LT2ESWTR (Long-Term 2 Enhanced Surface Water Treatment Rule) and NWRI/AWWA (National Water Research Institute/American Water Works Association) standards in the US as well as the UKWIR (UK Water Industry Research) report and CIWEM (Chartered Institution of Water and Environmental Management) standards locally in the UK.
In another lecture, entitled UV Disinfection – US Status Overview2 , the topic of UV was reviewed from the historical, regulatory and research perspectives. The lecture began with outlining the increased awareness of Cryptosporidium, accelerated by the Cryptosporidiosis outbreak in Milwaukee, WI in 1993.
In addition, the lecture reviewed studies conducted in this field from 1995 to 1999, leading up to the US EPA’s LT2ESWTR. According to these rules, source water should be monitored, data related to Cryptosporidium findings should be collected, a Cryptosporidium treatment bin should be set and treatment according to the microbial toolbox should be implemented (Table 1).
A presentation entitled UV Guidelines – US 3 expanded on the subject of guidelines in the US. This included references to sponsoring agencies and applications. (Table 2)The LT2ESWTR, which refers to drinking water systems of all sizes, is the most common. It requires specific UV doses, validation of the reactor and monitoring and reporting performances.
Another paper, entitled UV Guidelines in Europe4, reviewed the background of the need for preventing water-borne illnesses caused by bacteria, viruses and parasites. The safety level is typically characterized by a reduction of three to five logs of the concentration of pathogenic microorganisms to achieve a residual risk of 1:10,000 (annual infection risk set by the World Health Organization and the US EPA).
Existing European standards were reviewed, including the German standard (DVGW), the Austrian standard (OMORM – applied in Austria, Germany, Switzerland, Norway and Eastern Europe) and The European Committee for Standardization Technical Committee (CEN–Comite’ European de Normalization) 164 for treatment inside buildings. The common denominator of these three standards is that they require a reduction equivalent UV fluence (dose) of 400 J/m2 (equals 40 mJ/cm2) and that they require full-scale validation tests (Biodosimetry).
Another paper entitled A comparison of UV–disinfection, ozone and membranes for Cryptosporidium control based on existing projects5, which characterized the treatment of Cryptosporidium based on three categories: destruction, inactivation and physical removal. In addition, this presentation described UV projects trends in the USA, including maintenance of residuals in the distribution system, increased emphasis on Cryptosporidium monitoring and effective disinfection without producing excessive levels of DBPs.
The presentation reviewed the various existing technologies for Cryptosporidium treatment (Table 3). In general, trends in the US indicate that a combination of membrane and disinfection treatment is the most efficient solution and there is an increase in the use of UV irradiation for Cryptosporidium disinfection.
The Small System Guidance6 lecture opened with a definition by the US EPA of small systems, very small systems that serve a population ranging from 25 to 500, or that serve a population ranging from 501 to 3300. At the global level, 2.5 billion people receive their water supply from small systems. However, there are problems in operating these systems due to lack of resources including knowledgeable personnel, time and money.
Disinfection alternatives were described, such as free chlorine, chlorine dioxide and ozone, with the advantages and drawbacks of each method listed. Among the advantages of UV technology, it was identified as very effective against Cryptosporidium, Giardia and many viruses, as well as being compact and not requiring chemical application.
A UV dose of 15 – 30 mJ/cm2 is sufficient against most bacteria. Research data indicates that a UV dose of 8 – 20 mJ/cm2 produces 4-6 log inactivation. Regarding viral inactivation, data suggests that adenovirus is more resistant; 60 mJ/cm2 results in only one-log inactivation.
A representative of the DWI presented the final lecture on UV and control of Cryptosporidium – A regulator’s perspective9. This expanded on the subject of recent changes made in the UK in recognition of UV as a method for Cryptosporidium control.
Historically, the only acceptable risk control measures for Cryptosporidium have been based on physical removal, such as membrane filtration. However, recent new regulations allow the use of alternative technologies other than physical removal to be used as a risk-control measure.
The new guideline developed by DWI was currently in draft at the time of this workshop. It was also noted that UV disinfection is fully effective on water free of particles; therefore it must always be installed downstream of all particulate removal processes. In addition, regulation requires that water leaving treatment works should have turbidity lower than one NTU.
This lecture also expanded on the issue of the importance of validation and monitoring of UV plants. It noted that installing UV is not a substitute for filtration and does not remove the responsibility of companies to look at catchment initiatives for controlling risks from Cryptosporidium.
To order a CD of the entire workshop and its technical presentations, contact the International Ultraviolet Association (www.iuva.org), to the attention of Diana Schoenberg at DianaS@iuva.org. For more information on WRc PLC, please visit them online at http://www.wrcplc.co.uk. For more information on IUVA Organization, please visit them online at http://www.iuva.org.
- Templeton, M., (2008) Cryptosporidium UV-disinfection of drinking water: Opportunities and limits. Proceedings of the IUVA workshop –Cryptosporidium control in drinking water with UV disinfection: Status,experience, development and outlook, Imperial College, London, Sept. 15,2008.
- Hulsey, B., UV disinfection – US status overview. Proceedings of the IUVA workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
- Malley, J. P. Jr and Cotton, C., UV Guidelines – US. Proceedings of the IUVA workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
- Sommer, R., UV Guidelines in Europe. Proceedings of the IUVA workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
- Awad, J., A comparison of UV – disinfection, ozone and membranes for Cryptosporidium control based on existing projects. Proceedings of the IUVA Workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
- Malley, J., Small system guidance. Proceedings of the IUVA workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
- Sakaji, R., Operational experience with UV in the US. Proceedings of the IUVA workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
- Joyce, M. and Hanley, R., Operational experience with UV in Europe. Proceedings of the IUVA workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
- Cordiner, E., UV and control of Cryptosporidium A Regulator’s perspectiveand Cryptosporidium UV-Disinfection of drinking water: Opportunities and limits. Proceedings of the IUVA workshop – Cryptosporidium control in drinking water with UV disinfection: Status, experience, development and outlook, Imperial College, London, Sept. 15, 2008.
About the author
Anat Kartaginer is head of the Water Treatment Department at Tana Water of Emek Haela, Israel. She is a member of the Israeli Water Association (IWA), European Point-Of-Use Drinking Water Association (EPDWA) and the WC&P Technical Review Committee. She can be reached at +972.2.990. 0222 (phone), by fax at +972.2.990.0500, by e-mail at email@example.com or through the company’s website http://www.tanawater.com.
The author would like to thank Professor Ronald Gehr of the Department of Civil Engineering at McGill University in Montreal, Quebec, Canada, for his assistance in writing this paper. Danny Targan, Chief Executive Officer of Tana Industries, is also to be commended for his encouragement and support.
About the company
Tana Water has been a major force in the provision of drinking water systems for over 30 years and is one of the world’s most advanced developers and manufacturers of POU systems. Leading-edge products are matched by a focus on customer service, which comes from long-lasting partnerships with clients. Visit the website, www.tanawater.com to learn more.