Nutrient Removals by
Conventional Treatment Processes
W. K. Johnson, Lecturer
Department of Civil Engineering, University of Minnesota,
Minneapolis, Minn.
The removal of nitrogen and phosphorous from sewage has not
been of general interest to the sanitary engineering profession and only
in a few cases the concentration of these elements in the effluents from
sewage treatment plants has been considered to be the cause of nuisances.
Receiving streams and lakes remain in a comparatively static condition
regarding their size while urban communities continue to grow and contribute more wastes to these bodies of water. Although the biochemical
oxygen demand (BOD) of a waste entering a body of water may be
sufficiently low so as not to result in any serious depletion of dissolved
oxygen (DO), quantities of nitrogen and phosphorus added from the
waste could very likely contribute toward excessive growths of objectionable algae and other plants. It appears that the problem of removing nutrients from sewage is becoming increasingly important.
CHARACTERISTICS AND QUANTITY OF NUTRIENTS
The nitrogen in a raw waste is usually found either as organic
nitrogen or as free ammonia nitrogen. Small quanties of nitrogen as
nitrites and nitrates may also be present. As with the concentrations of
any constituent in sewage the actual concentrations of each form of
nitrogen varies considerably. In a study of 15 cities by the writer
together with data assembled by Stanley (1), the average nitrogen
contents of the raw wastes were found as presented in Table I.
The average value for nitrogen content agrees quite well with data
given by Babbitt (2) who considered a weak sewage as having a total
nitrogen content of 25 ppm with 10 ppm in the organic form and 15 ppm
present as ammonia.
The organic nitrogen most likely exists primarily as protein compounds and their products of decomposition along with urea. The exact
forms of organic nitrogen were distinguished to some extent by Heukele-
kian (3) who found that very little of the organic nitrogen of cotton
filtered domestic sewage was removed by filtration through a Seitz filter.
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