Effect of sewage loading on the prevalence of Sphaerotilus natans.

Although biological treatment of sewage by activated sludge or trickling filters is widely practiced, these processes still give rise to difficulties. The difficulties may be due to sludge bulking during the activated sludge process or to clogging during the operation of trickling filters. In his studies of biofilters and standard filters, H. Heukelekian (Sewage Works J. 17:23, 516, and 743, 1945; Ind. Eng. Chem. 41:1412, 1945) has demonstrated a relationship between film accumulation and nitrifying and purifying capacity. Sewage usually contains a variety of filamentous growths ranging from bacteria to the ramifying branched mycelia of true fungi. Undesirable bulking of activated sludge in sewage treatment plants is attributed to the development of a species of Sphaerotilus (N. C. Dondero, R. A. Phillips, and H. Heukelekian, Appl. Microbiol. 9:219, 1961; J. B. Lackey and E. Wattie, Public Health Rept. U.S. 55:975, 1940; D. A. Okun, Sewage Works J. 21:763, 1949; C. C. Ruchhoff and J. F. Kachmar, Sewage Works J. 18:1, 1941). Several reports on this subject have appeared, and, as a consequence, the organism has been widely studied. The work so far carried out has been mainly confined to the isolation and identification of the different species of Sphaerotilus occurring in treated sewage. Although these observations have added considerably to the understanding of some of the biological aspects of waste treatment, further work is needed, particularly on the effect of loading on the development of S. natans during biological treatment. In the course of an investigation of this aspect of sewage