Field studies on coliphages and coliforms as indicators of airborne animal viral contamination from wastewater treatment facilities

Abstract

The occurrence of animal viruses in the aerosol emissions of wastewater treatment facilities was evaluated by direct assay and by the use of coliforms and coliphages as indicator organisms. Coliforms and coliphages were compared and evaluated with regard to their suitability as indicators of airborne animal viral contamination from wastewater treatment facilities. Two plants, one with treatment by activated sludge and the other by trickling filtration, were studied. Field air sampling procedures used large-volume air samplers, with recirculation devices, and Andersen samplers. Airborne viruses were enumerated by a most probable number (MPN) procedure. Partially treated liquid sewage contained about 1.0 × 10 2 pfu l −1 of animal viruses assayed on Buffalo Green Monkey (BGM) cells, 3.6 × 10 5 and 5.0 × 10 5 pfu l −1 of coliphages, depending upon the E. coli host strain used for assay, and 2.0 × 10 9 colonies l −1 of coliform bacteria. No airborne animal viruses were recovered, airborne coliphage levels averaged 2.3 × 10 −1 and 3.0 × 10 −1 MPN m −3, coliforms from aerosol emissions were 2.1 × 10 2 colonies m −3. Ratios of coliphages to animal viruses indicate that wastewater treatment plants may be continuous sources of low level concentrations of animal virus aerosols. Evidence shows coliforms to be much less stable than coliphages in the airborne state. Coliphages may be a more acceptable indicator of airborne animal viral contamination than coliforms.