Report No FR0229

T N Whitmore and P Gray

Sept 1991



The objectives of this contract are to improve methods for the primary separation of Cryptosporidium oocysts for monitoring purposes and to estimate the levels of oocysts in sewage effluents to ascertain the influence of such effluents upon the quality of the receiving waters. A study of the levels of Cryptosporidia in source, distributed and receiving waters and the levels of Cryptosporidiosis in the human and animal populations in the Loch Lomond southern catchment and distribution is being funded jointly with the Central Scotland Water Development Board.


Cryptosporidia have recently been recognised as waterborne pathogens. The current recovery methods for oocysts are time consuming and of low efficiency. Data on the occurrence and survival of oocysts in water is sparse. Infected persons excrete large numbers of oocysts and thus the levels in sewage effluents are potentially high.


Through the use of spiked waters several methods were evaluated for their potential to recover Cryptosporidium oocysts. Sand column filtration and vortex flow filtration were judged to be too slow for the processing of the large volumes of water required for environmental sampling. Preliminary results with glass microfibre cartridge filters have been more promising and worthy of continued evaluation. The monitoring of sewage effluents and the Lomond study have been initiated. However as yet insufficient data are available for any conclusions to be drawn.


These will be made on completion of the contract.


Several methods have been evaluated for the primary separation of Cryptosporidium oocysts. In summary the vortex flow filtration technique using the "Benchmark" device gave fairly consistent recoveries of 30-40%. However the recovery rate was found to be too long to be practical for the processing of large volumes of water which would be necessary for environmental monitoring purposes. Laboratory scale sand columns were also evaluated. The retention within the column material was satisfactory at low flow rates. However the system was judged inadequate for environmental monitoring because of the poor retention of oocysts within the column matrix at realistic flow rates. Glass microfibre cartridge filters of nominal pore size 2m have been tested using oocyst spiked borehole water at a flow rate of 1.5l/min. Preliminary trials resulted in recoveries of over 30%. Filters of smaller pore size (0.9m) are currently being evaluated to determine whether improved recoveries will be obtained.

The monitoring of effluents from a cattle market has been initiated and the possibility of studying other sewage effluents is being considered.

The Lomond Study is reported separately and is included as an appendix to this report.

Copies of the Report are available from FWR, price 15.00 less 20% to FWR Members