Viruses in sewage: effect of phosphate removal with calcium hydroxide (lime)

During calcium hydroxide (lime) treatment (pH 9.6 to 10.5) of wastewaters for phosphate removal there was also a two-log removal of added poliovirus (type I, Sabin) from effluents. A similar virus reduction was seen in the sludge generated in these experiments. However, in view of the limitations of techniques for virus recovery from sludge, only a small portion of the infectious virus present in lime sludge may have been detected. Storage of lime sludge at 28 degrees C for up to 48 h produced no appreciable reduction in the virus titre. Five sets of field samples of sewage, effluents, and sludge from a sewage treatment plant (Kemptville, Ont.) which utilizes lime for phosphate removal were also examined for indigenous viruses being BS-C-1 cells. All of the sample of lime sludge and 80% of the samples of both sewage and lime-treated effluent revealed virus; after chlorination only 20% of the lime-treated effluent samples were positive for virus. In contrast, in an earlier study with essentially the same experimental set up, 76% of the sample of chlorinated primary effluent were found to contain virus. Because of the easily detectable quantities of infectious virus in lime sludge and due to the lack of virus inactivation during storage of such sludge, caution must be exercised in its handling and disposal.