UV Biodosimetry Using MS2 Coliphage

By R.C. Cooper

The use of ultraviolet light as a means to disinfect water and wastewater has gained in popularity because of limited production of disinfection byproducts and its effectiveness in inactivating pathogenic microorganisms, particularly Cryptosporidium sp. One of the important operational parameters in the design and evaluation of the UV treatment is the cumulative UV dose delivered as the water to be treated flows through the irradiation (disinfection) process.

The UV dose is a product of the intensity of the light at a given distance from the lamp and the time of exposure. Using photometric equipment, this dose can be measured in the treatment process only at specific points and at fixed distances from the lamp; which, because of hydraulic vagaries and varying distance from the lamp(s), gives only a limited measure of the dose that a microorganism might receive during its passage through the UV treatment unit. In order to overcome these limitations biodosimetry is employed. Biodosimetry is a method by which an integrated value for the dose received during passage through the UV unit can be estimated using microorganisms that have known UV dose response characteristics.

At the present time the microorganism of choice for biodosimetry is the MS2 coliphage, a bacterial virus that infects specific species of Escherichia coli and responds to doses of UV in a very consistent manner. In order to measure the dose produced by a treatment process the water to be disinfected is seeded with a known concentration of MS2 coliphage and passed through the UV unit. After an appropriate flow time has elapsed effluent samples are collected and analyzed for MS2 coliphage levels. The degree of virus inactivation is calculated as the difference between the Log10 of the influent and effluent phage numbers. The dose of UV required to cause this magnitude of virus reduction can then be estimated from an understanding of how this virus responds (is reduced in numbers) to varying UV doses.

The dose response characteristic (dose response curve) of this virus is determined by collimated beam assay. In this analysis a device is used that produces a beam of UV light of uniform intensity, i.e. collimated, on to a solution of known depth containing the MS2 coliphage at a predetermined concentration. Being collimated the intensity of the UV beam is uniform across the surface of the irradiated solution. Knowing the intensity of the beam, the UV absorbency characteristic of the water matrix and depth of the solution the dose (intensity x time) delivered after any given time of exposure can be calculated. The numbers of MS2 viruses surviving after measured exposure time periods are determined and a dose response curve is generated such as is shown in Figure1. As an example, using the dose response curve, if a 4 log reduction in MS2 numbers is seen through the unit it would indicate that a dose of 100mJ/cm2 was delivered by the UV treatment system. This value is also referred to as the RED for Reduction Equivalent Dose. The data from which this Figure was generated were the results of dose response values (181 data points) collected from 45 different batches of MS2 produced by BioVir Laboratories. The curve displayed is the result of a linear regression analysis of the data. The R2 statistic for the curve "fit" is 0.926 which is an indication of the uniformity of the MS2 response to UV254 doses.

 

BioVir can produce multi Liter volumes of MS2 coliphage at concentrations of 1 x 1011 plaque forming units (Pfu) per mL. This concentration and volume of phage allows for seeding UV systems in water reclamation plants with capacities of over 1mgd with phage of known UV sensitivity. Since these viruses have limited if any environmental impact and are not infectious to humans or animals they are safe to use in these applications.

Phage

Bacteriophage  (pdf.)

NWRI UV Guidelines

EPA Method 1601/1602



(Back to main Services page)


© 2014 BioVir Laboratories.