Abstract
The behaviour of f2 coliphage and poliovirus I in activated sludge treatment was studied under different operating conditions of flow through time, mixed liquor suspended solids, temperature and virus loading in a bench scale model plant whose performance was similar to that of a full scale treatment plant. The liquid and solids fractions of mixed liquor samples containing virus were assayed separately, with the solids fraction receiving ultrasonic treatment. The recovery of poliovirus from mixed liquor by this method was about 83%, while that of f2 coliphage was in the range of about 54-85%. The average removal of f2 coliphage across the model plant was about 84 %, and was not significantly altered by altering the flow through time, mixed liquor suspended solids and temperature in the plant. The removal was, however, decreased from about 96 % to about 70% with higher virus loads. The association of f2 with the mixed liquor solids showed an inverse relation with increased flow, a direct relation with increased mixed liquor solids, and apparently direct relation (with an optimum) with increased temperature and a clear direct relation with increased virus load. The removal of poliovirus across the plant over the range of conditions studied was generally high and reached up to about 99.7 %. The behaviour and removal of both viruses in the model plant correlated with the association of these viruses with the suspended solids. The degree of association, which appeared to depend upon the nature of each virus and was achieved by physical adsorption, was strikingly contrasting with about 18 and 85 % of f2 and poliovirus respectively detected on the solids. The striking differences between the behaviour of f2 coliphage and poliovirus I imposed interesting implications on the concept of indicator virus from the public health viewpoint.