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NHMRC Public Consultations

Open Public Consultations

Public consultation on Australian Drinking Water Guidelines - Information Sheets for Water Treatment Operators

Closing Date - 26 Apr 2013 - 5:00pm

 

Information Sheet 1.7

Disinfection with Germicidal ultraviolet light

From:

Rob Wilson

UVS Ultra Violet Pty Ltd

10 Christensen Street

Cheltenham Vic 3192

 

rw@uvsultraviolet.com.au

 

Brief History of UVS:

 

Originally founded in 1947, UVS has being manufacturing Low-pressure Mercury Vapour Germicidal Ultra Violet Lamps for over 40 years. With the assistance of a number of Government Grants, we have spent a total of 15.57 million dollars, to-date, on many Research and Development Projects dealing with the constant improvement with the UV Output of the various UV lamps, and the UV Water Disinfection Units. Hundreds of Full Scale Bio-assay testing were performed, by the former NATA Registered MicroTech Laboratories, (Now owned by Silliker Laboratories Group) to determine the Microbiological performance and therefore the Total UV Dosage. The following challenge micro-organisms were used, Bacillus subtilis spores, Micrococcus lutea, Escherichia coli, Klebsiella terrigena, Legionella pneumophila, Vibrio cholerae, Aspergillus niger, Bohle iridovirus, Bovine enterovirus, Fusarium oxysporum, Phytophthora cinnamomi zoospores, Phytophthora cinnamomi chlamydospores, to name a few.

 

I have run all R&D over the past 40 years.  

 

Information Sheet 1.7

Disinfection with Germicidal ultraviolet light

 

General description

Germicidal Ultraviolet light (UV) is generated by low and medium pressure mercury vapour lamps. UV irradiation disrupts the chemical bond of many organic molecules and damages nucleic acid and hence can be a potent disinfectant. The UV light effective for inactivating microorganisms is in the UV-B and UV-C ranges of the spectrum (200–300 nm), with maximum effectiveness around 265 nm.

The mechanism of disinfection by UV light differs considerably from the mechanisms of chemical disinfectants such as chlorine and ozone. Chemical disinfectants inactivate microorganisms by destroying or damaging cellular structures, interfering with metabolism, and hindering biosynthesis and growth (Snowball and Hornsey 1988). UV light inactivates microorganisms by damaging their nucleic acid, thereby preventing them from replicating and disrupting their ability to infect hosts.

UV irradiation has a minimal effect on the chemical composition or taste of water. Unlike chemical disinfectants, high dosage or over-dosing with UV presents no danger, and is sometimes considered as a safety factor.

 

Performance validation

 

UV performance will vary depending upon a number of variables including water quality, flow rate, lamp performance, configuration of equipment and power quality/reliability.  Thus it is important that system validation and performance are undertaken on a case-by-case basis.

 

This cannot be underestimated, or understated. 

Because a wavelength of LIGHT is providing the ability to achieve the required percentage disinfection, there are a number of questions that must be answered to enable the calculation to determine the type of unit, the number and type of UV lamps. The information necessary to provide the successful Germicidal Ultra Violet Disinfection is shown below:

 

A) Percentage UV Transmittance at 254 nm using 1 cm Fused Quartz Cells

B) Flow Rate in L/sec, L/Hr, or m3/sec, (or per hour)

C) The Micro-organism(s) that the Client requires to be controlled

D) The Percentage Kill Rate Required for the Particular Application, e.g. 99.9%, 99.99%, etc

E) The above, to enable the Total UV Dosage, in µWsec/cm2 or mJ/cm2, to be determined

 

The Hydraulics of any UV Water Disinfection Unit is extremely complex, due to constantly changing Flow Rates, and cannot be accurately modelled even using complex Computational Fluid Dynamics, (CFD) software, due to the Randomised Nature of Turbulence. The ONLY way to be able to determine the actual Total UV Dosage of any UV Water Disinfection Unit is through Full Scale Bio-assay Testing.  (Biodosimetry)

 

If a UV Water Unit displays Laminar Flow conditions, then the Irradiance Measurement used to determine the Total UV Dosage, must be the minimum value at the internal wall of the unit. The Flow through the UV Unit can be Laminar, Transition, or Turbulent and all of these conditions will greatly influence the Total UV Dosage value.

 

Total UV Dosage cannot be measured in Real Time. No amount of UV-C Detectors will enable this to be achieved. In a multi lamp UV Water Disinfection Unit, the Irradiance Measurement is cumulative at any given point between any number of UV lamps.

 

The key to guaranteeing that the Total UV Dosage required is actually achieved, is Validation.

This must be at the forefront of any Guidelines for Percentage UV Disinfection, for without it, the Guidelines would be useless.  

 

 

Hijnen et al (2006) undertook an extensive literature review of existing data to provide guidance on the effectiveness of UV against a range of microorganisms.  Table IS 1.8.1 provides a summary UV doses required to achieve 2 log inactivation of a range of microorganisms.

 

This is the problem; Hijnen et al (2006) undertook an extensive literature review of existing data to provide guidance on the effectiveness of UV against a range of micro-organisms, nothing was done to determine the accuracy of the testing performed.

 

Extensive testing performed for the Austrian National Standards ÖNORM M 5873-1, and by MicoTech Laboratories for UVS, show that a Total UV Dosage of 60 mJ/cm2 will provide a 4-log reduction against Bacillus subtilis spores, but under Table 6 of the Hijnen et al (2006) review 222 mJ/cm2 is required to achieve the same log reduction. All of the testing which we had performed over many years did not show this difference between Laboratory Cultures and Environmental Strains.

 

Table IS1.8.1  Examples of dosage rates to achieve 99% (2 log) inactivation of various microorganisms by UV irradiation

 

Organism

Dosage for drinking water (mJ/cm2) to achieve 2 log removal

Bacteria

Bacillus subtilis

111

E. coli O157

9

E. coli

9

Legionella pneumophila

15

Campylobacter spp.

7

Yersinia enterocolitica

7

Clostridium perfringens

95

Streptococcus faecalis

16

Shigella dysenteriae

5

Vibrio cholerae

4

Salmonella typhi

12

Viruses

Adenovirus type 40

111

Adenovirus type 2, 15, 40, 41

83

Adenovirus

50

Rotavirus SA-11

20

Coxsackie virus B5

17

Poliovirus type 1

15

Hepatitis A

11

Protozoa

Cryptosporidium

6

Giardia

5

Acanthamoeba

71

Based on Hijnen et al. (2006)

 

For protozoa, the outcomes of recent investigations (Clancy et al.,1998ab; Bukhari et al.,1999; USEPA, 2006; Craik et al., 2000) using mouse infectivity or cell culture showed that low or medium-pressure mercury vapour UV lamps, or pulsed UV technology, can achieve 3-log inactivation of Cryptosporidium oocysts and Giardia at UV doses less than 15 mJ/cm2.

 

The important conclusion to draw from Table IS1.8.1 is that, at the typical dose rate used in Australian drinking water supplies (i.e. 40 mJ/cm2)

 

It is my experience having being in the UV Industry for over 45 years, that 40 mJ/cm2 is not typical, and if quoted, is seldom achieved.

 

It is very important that if a Total UV Dosage of 40 mJ/cm2 is specified, then it must be at End of UV Lamp Life. With the technology today of using internal coatings, this is 12,000 hours, but there are still many UV lamps used, which still only have a 9,000 hour Effective UV Lamp Life.

 

Even with the use of high output Amalgam Lamps, the reduction in UV Output under actual Field Operating Conditions, will still be around 25% after 12,000 hours operation of the Lamps.

 

It is very important that any Total UV Dosage value specified must be at End of Lamp Life.

 

UV will effectively inactivate most vegetative bacteria and protozoa, but will not be effective against all types of virus.

 

Given that the UV process will be a critical control point (CCP), other important issues that will need to be considered to ensure the effectiveness of the process are:

  • establishing target criteria (section 3.4.2) and critical limits for the UV irradiation process
  • preparing and implementing operational procedures (section 3.4.1) and operational monitoring (section 3.4.2) for the process
  • preparing corrective action procedures (section 3.4.3) in the event that there are excursions in the operational parameters
  • undertaking employee training (section 3.7.2) to ensure that the UV irradiation process operates to the established target criteria and critical limits

 

It is recommended that validation is undertaken for each system to ensure appropriate treatment is in place for the water quality and level of risk.

 

Water quality considerations

 

The performance of UV disinfection is not affected at turbidity levels of 1 NTU, and UV may remain effective at higher turbidities than 1 NTU, as long as the transmittance of UV through the water is not compromised.  However, the lower the turbidity of the water the more effective the performance of UV will be. 

UV irradiation is not pH dependent and the temperature effect between the ranges of 5 to 35oC is minimal (USEPA 2006).  The presence of algae in the water being treated may reduce the UV transmittance and interfere with the UV disinfection process and should be considered in the design phase if the supply is prone to algal blooms.

Highly coloured water is not suitable for UV disinfection as the dissolved organic matter which gives the water its colour strongly absorbs the UV light, greatly reducing the effectiveness of the UV disinfection process.

 

By far the most important Water Quality consideration is Percentage UV Transmittance. We have successfully designed UV Water Disinfection Units to operate at 20% UVT. (The Water Film thickness is very small) We never measure the Turbidities, as they are only one component which makes up the Percentage UV Transmittance of the Water.

 

Practical considerations

 

The equipment required for UV irradiation is fairly reliable, the technology required is relatively simple and controls for the process are being developed. There are a number of factors that should be considered in relation to UV such as:

  • reliability of power supply, in particular the start-up and restart times should be factored into operational and response plans;

The use of the correct Electronic Ballasts provides constant Current outputs.

  • water quality aspects, such as algae, high colour and turbidity, hardness and organic matter, as they can reduce the amount of UV radiation reaching microorganisms and necessitate higher doses of applied radiation for effective disinfection;

Knowing the Percentage UV Transmittance covers all of the above.

  • a site-specific mercury spill response plan should be established to minimise mercury release in the event of a lamp breakage; and,

The amount of Liquid Mercury in a UV lamp is in the order of milligrams, and the UV Lamp resides inside a Fused Quartz Sleeve. In 40 years I have never seen a UV Lamp broken while in its normal operation.

  • Units require regular cleaning and maintenance to remain effective.

Absolutely

 

 

Persistence

 

At the proper dosage, UV requires only a short contact time, but has the disadvantage that it leaves no residual disinfectant, which would provide an additional barrier within the distribution system.

 

By-products

 

Few data are available on the by-products of UV disinfection. At the UV doses typical for drinking water supplies (less than 200 mJ/cm2), there is no evidence of the formation of by-products or exacerbation of DBP’s if post UV disinfection occurs (USEPA 2006).

 

UV has been reported to convert nitrate to nitrite at a conversion rate of approximately 1% (Sharpless and Linden, 2001).  Given the typical values of Australian waters, the nitrate to nitrite conversion is unlikely to result in the exceedance of health guidelines for drinking water.

 

Application

 

UV disinfection is a treatment option that can contribute to the effective implementation of a multi-barrier approach that reduces microbial risk in drinking water supplies.  UV disinfection can be used as the primary disinfectant for the inactivation of chlorine resistant pathogens (e.g., Cryptosporidium and Giardia), thereby reducing DBP formation. However, UV disinfection typically should not completely replace the use of chemical disinfection.  This is because there are a number of other aspects to consider in managing the microbial risk of drinking water supplies, such as:

  • maintaining a disinfection residual within the distribution system;
  • management of taste and odour compounds;
  • controlling cyanobacteria;
  • deactivation of viruses that are not easily treated by UV alone; and
  • ensuring there is an adequate multi-barrier approach for the entire drinking water system. 

 

Operational monitoring

As there is no disinfection residual to measure following UV treatment, other operational aspects of UV systems should be monitored to ensure that the treatment system is operating as expected.  Examples of monitoring parameters are listed below, recognising that each system will need to develop its own operational monitoring specifications reflecting its unique circumstances.

  • UV dose

Total UV Dosage cannot measured, or Calculated in Real Time

  • Flow rate
  • Turbidity

I see no point in measuring Turbidity where you are measuring the %UVT.

  • UV transmittance
  • Lamp outage

Absolutely

 

Other issues that need to be considered with respect to UV is that the performance of the UV lamps deteriorates over time, so that lamps should be changed at the frequency recommended by the manufacturer. Furthermore, biofilm, which can accumulate on the sleeve surrounding the lamp, should be regularly removed from the sleeve.  Many UV systems now have automated cleaning systems.

 

Typically the loss of UV Output is around 25% over 12,000 hours operation.

 

In Summary:

 

It is of the utmost importance for any Australian Drinking Water Guidelines which are going to allow the use of Germicidal Ultra Violet Light for the Disinfection of Water, to specify a Total UV Dosage value at End of Lamp Life, and then Validation through Full Scale Bio-assay Testing. (Biodosimetry)

 

If I can provide any further information, or clarification, please let me know.

 

Rob Wilson

 

 

References

 

Bukhari Z et al. (1999). Medium-pressure UV light for oocyst inactivation. Journal of the American Water Works Association, 91(3):86–94.

 

Clancy JL et al. (1998a). Inactivation of Cryptosporidium parvum oocysts in water using ultraviolet light. Journal of the American Water Works Association, 90:92–102.

 

Clancy JL et al. (1998b). Innovative electrotechnologies for Cryptosporidium inactivation. CR-111090. Electric Power Research Institute, Palo Alto, CA.

 

Craik SA et al. (2000). Inactivation of Giardia muris cysts using medium-pressure ultraviolet radiation in filtered drinking water. Water Research, 34(18):4345–4332.

 

DVGW (2006a) UV Devices for Disinfection in the Water Supply Part 1: Requirements Related to Composition, Function and Operation, in Technical Rule, Code of Practice W294-1.

 

DVGW (2006b) UV Devices for Disinfection in the Water Supply Part 2: Testing of Composition, Function and Disinfection Efficiency in Technical Rule, Code of Practice W294-2

 

DVGW (2006c), UV Devices for Disinfection in the Water Supply; Part 3: Measuring Windows and Sensors for the Radiometric Monitoring of UV Disinfection Devices: Requirements, Testing and Calibration in Technical Rule, Code of Practice W 294-3

 

Hijnen, W.A.M., Beerendonk, E.F. and Medema, G.J (2006) Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cysts in water: A review.  Water Research 40: 3-22.

 

Sharpless, C.M., and K.G. Linden. 2001. UV photolysis of nitrate: Effects of natural organic matter and dissolved inorganic carbon, and implications for UV water disinfection. Environmental Science and Technology 35:2949–2955.

 

USEPA. 2006. Ultraviolet disinfection guidance manual for the final long term 2 enhanced surface water treatment rule. EPA 815-R-06-007. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

 

Page reviewed: 17 December, 2013