AlternativeMicrobiological Indicators of Water Quality

ReportNo WSAA 150

February 1999

 

SUMMARY

 

Concentrationof viruses and protozoa from water has been notoriously difficult. Due to thesmall numbers of these pathogens in environmental waters and drinking water,concentration of large volumes of water is required, adding to the difficultyof the test. Methods often used may be slow, laborious, have poor recoveryefficiencies, or require expensive equipment. Various methods to concentrateviruses and protozoa (Giardia cystsand Cryptosporidium oocysts) fromwater were evaluated to determine the optimum methods in terms of virusrecovery, ease of use, labour and material costs.

 

Methodstested for concentration of viruses were ultrafiltration and various adsorption/elutionmethods including adsorption to negatively charged surfaces (glass powder andwound fiberglass cartridge (Diamond filters) and positively charged surfaces(1MDS cartridge filters and oiled sodacalcic glass wool). The optimum method interms of virus recovery combined with ease of use was the oiled sodacalcicglass wool. Material costs were low and the method easy to use. Recoveryefficiencies of greater than 60% were achieved using packed glass wool columnson most water types. However, recovery efficiencies were lower (<40%) forpotable water samples with low electrical conductivity (EC<500 ÁS/cm). Therecovery efficiency of enteroviruses in this type of water sample should bedetermined prior to use in order to make sense of results obtained.

 

Twomethods were evaluated for the concentration of Giardia cysts and Cryptosporidiumoocysts. Ultrafiltration was found to be unsatisfactory since the unit couldnot be sufficiently cleaned and carry-over of seeded oocysts into negativecontrol samples was observed. Diamond filters were also evaluated, with averagerecovery 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.

 

Amethod which could concentrate both types of pathogens simultaneously wasdesired. There were two means of achieving this objective: to eitherconcentrate the pathogens using a single method, or to concentratesimultaneously with a different method for each pathogen type. Ultrafiltrationand Diamond filters were theoretically able to concentrate both pathogenssimultaneously. However, ultrafiltration was found unsuitable due to carry-overof oocysts into negative controls, and the wound fiberglass cartridge filtersdid not adequately concentrate viruses. Furthermore, using the wound fiberglasscartridge filter for virus concentration required lowering of the sample pH to3.5 and the addition of trivalent cations to the sample, making the method alaboratory based procedure.

 

Themethods which best concentrated protozoa and viruses were Diamond filters andoiled sodacalcic glass wool, respectively. An attempt to place these filters inseries was unsuccessful due to the adsorption of viruses to dirt particleswhich were retained by the Diamond filter and did not pass through to the glasswool column. An apparatus could be designed where the two filters are placed inparallel and the stream of water sample split between them. In this way, thetwo pathogen types could be simultaneously concentrated which reduces samplingtimes. In addition, although two different filters would be used, these filterswere shown to be the most efficient means of concentrating viruses and protozoatested in this study.

 

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