Alternative Microbiological Indicators of Water Quality
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report No UWRAA 150
Concentration of viruses and protozoa from water has been notoriously difficult. Due to the small numbers of these pathogens in environmental waters and drinking water, concentration of large volumes of water is required, adding to the difficulty of the test. Methods often used may be slow, laborious, have poor recovery efficiencies, or require expensive equipment. Various methods to concentrate viruses and protozoa (Giardia cysts and Cryptosporidium oocysts) from water were evaluated to determine the optimum methods in terms of virus recovery, ease of use, labour and material costs.
Methods tested for concentration of viruses were ultrafiltration and various adsorption/elution methods including adsorption to negatively charged surfaces (glass powder and wound fiberglass cartridge (Diamond filters) and positively charged surfaces(1MDS cartridge filters and oiled soda calcic glass wool). The optimum method in terms of virus recovery combined with ease of use was the oiled soda calcic glass wool. Material costs were low and the method easy to use. Recovery efficiencies of greater than 60% were achieved using packed glass wool columns on most water types. However, recovery efficiencies were lower (<40%) for potable water samples with low electrical conductivity (EC<500 µS/cm). The recovery efficiency of enteroviruses in this type of water sample should be determined prior to use in order to make sense of results obtained.
Two methods were evaluated for the concentration of Giardia cysts and Cryptosporidium oocysts. Ultrafiltration was found to be unsatisfactory since the unit could not be sufficiently cleaned and carry-over of seeded oocysts into negative control samples was observed. Diamond filters were also evaluated, with average recovery efficiencies of 50 and 42% respectively for Giardia and Cryptosporidium. These compared well to other methods previously tested at Water EcoScience, although the range of recoveries obtained was larger.
A method which could concentrate both types of pathogens simultaneously was desired. There were two means of achieving this objective: to either concentrate the pathogens using a single method, or to concentrate simultaneously with a different method for each pathogen type. Ultrafiltration and Diamond filters were theoretically able to concentrate both pathogens simultaneously. However, ultrafiltration was found unsuitable due to carry-over of oocysts into negative controls, and the wound fiberglass cartridge filters did not adequately concentrate viruses. Furthermore, using the wound fiberglass cartridge filter for virus concentration required lowering of the sample pH to3.5 and the addition of trivalent cations to the sample, making the method a laboratory based procedure.
The methods which best concentrated protozoa and viruses were Diamond filters and oiled soda calcic glass wool, respectively. An attempt to place these filters in series was unsuccessful due to the adsorption of viruses to dirt particles which were retained by the Diamond filter and did not pass through to the glass wool column. An apparatus could be designed where the two filters are placed in parallel and the stream of water sample split between them. In this way, the two pathogen types could be simultaneously concentrated which reduces sampling times. In addition, although two different filters would be used, these filters were shown to be the most efficient means of concentrating viruses and protozoa tested in this study.