Atmospheric Nitrogen Fixation in
Activated Sludge
FRANK B. KAYLOR, Sanitary Engineer
Solvay Process Division, Allied Chemical Corporation
Syracuse, New York
MOHAMMED H. BECHIR, Graduate Student
Massachusetts Institute of Technology
Cambridge, Massachusetts
JAMES M. SYMONS, Assistant Professor of Sanitary Engineering
Massachusetts Institute of Technology
Cambridge, Massachusetts
The object of this study was to determine the effectiveness of treating nitrogen-free wastes by atmospheric nitrogen fixation under activated sludge treatment. Nitrogen, carbon and phosphorous are three of the important basic elements
necessary for the growth of bacteria. Sawyer and his co-workers (1) established a
BOD/N ratio of 20/1 to permit the full unrestricted growth of bacteria in conven -
tional activated sludge treatment. Although domestic sewage meets this requirement easily, many industrial organic wastes do not and are termed "nitrogen-
deficient" wastes. It it were possible to use atmospheric-nitrogen-fixing organisms
to supply the nitrogen-deficient wastes, the addition of costly chemical nitrogen
as a bacterial nutrient could be avoided.
•     LITERATURE REVIEW
A limited number of genera of microorganisms have the ability to use molecular nitrogen in the atmosphere as their source of nitrogen for protein synthesis.
The conversion of molecular nitrogen into nitrogenous compounds is caUed nitrogen fixation. Two groups of microorganisms are involved in this process -- (1)
those that live freely and independently in the soil, and (2), those that live in
close association with the root system of leguminous plants. The former are referred to as non-symbiotic nitrogen fixers and the latter as symbiotic nitrogen fixers (2). The Azotobacter sp. are the non-symbiotic type and are more importnat
because they are aerobic,  can be found in sewage, and grow on many substrates.
Although there is ample literature concerned with the Azotobacter sp., the
application of nitrogen fixing organisms to activated sludge treatment has received little attention. Beard and Munson (3) in 1932 tried to establish nitrogen
fixation to treat a two per cent milk waste, but reported negative results. In
1941, Allen (4) used a glucose medium and a heavy seed of Azotobacter. A fter
18 days of operation, he obtained an increase in nitrogen as well as seven mg of
nitrogen fixed per gm of glucose destroyed, but settling was poor and the nitrogen
content of the effluent was high. In 1954, McKinney, Poliakoff and Weichlein
(5) successfuUy developed a nitrogen-fixing system to stabilize cirrus cannery
waste which was nitrogen-deficient. Their nitrogen-fixing aeration unit was
seeded with the commercial product, "Nitragen," which contained Rhizobium
(the symbiotic nitrogen fixers) as well as Azotobacter in the desiccated state.
Optimum efficiencies were obtained on the 15th day of aeration. The "Nitragen"
unit removed 97.6 per cent of the five-day BOD in 24 hrs of aeration.   This ef-
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