The Effect of Sewage Treatment on Viruses.

Abstract

Increasing population density will in tensify the treatment problems associ ated with sewage. While present sew age treatment practices, based largely on empirical standards, are apparently sufficient to make recognized outbreaks of water-borne disease a rarity in the United States, future demands on water supplies and uses of sewage may re quire a more flexible role for sewage treatment products. Prom a sanitary standpoint, the use of effluents and sludge should be preceded by the as surance that they are not harmful. The disinfecting action of chlorine on bacteria in sewage has received atten tion from many and has resulted in a general feeling that effluents in contact with 0.5 ppm combined residual chlo rine for 15 min are free of pathogenic bacteria and protozoans (1). Enda mebic cysts, however, are known to re quire more intensive treatment than coliform bacteria (2). Knowledge of the destruction of viruses by sewage treatment is limited to laboratory ob servations and to a very few plant studies. The work described here was undertaken to determine the types of sewage treatment that destroy viruses under operating conditions. The many isolations of viruses from sewage since bacteriophage (3) and poliovirus (4) were recognized as en teric agents were made chiefly for identification purposes or were associ ated with outbreaks of disease or were done for locating the source of infec tion. The question of destruction of virus by sewage treatment so far has stimulated little effort. Gear noted early (5) that poliovirus was still pres ent after settling in both the effluent and sludge, that humus tank effluent contained virus, but that final sand filtration and digestion of sludge de stroyed it. Mack et al. (6) find that ac tivated sludge treatment removes vi ruses but not completely, and there have been indications (7) that neither primary nor secondary treatment de stroys them.