Treatment    of Nitrogen Deficient
Organic Wastes by a Modification of the
Activated Sludge Process
C. V. RAMA RAO, Research Assistant
R. E. SPEECE, Assistant Professor of Sanitary Engineering
R. S. ENGELBRECHT, Professor of Sanitary Engineering
Department of Civil Engineering
University of Illinois
Urbana, Illinois
Biological treatment processes are commonly used to stabilize industrial waste
waters containing organic pollutants. In addition to an energy source, the microorganisms responsible for the removal of the organic pollutant must also be supplied with certain inorganic nutrients in order to sustain their life processes. Domestic sewage contains adequate quantities of these inorganic nutrients to supply
the demand of the microorganisms. However, many industrial waste waters do not
contain sufficient nitrogen to satisfy the requirement of the microorganisms involved. Therefore, in order to satisfactorily stabilize these organically polluted
waste waters, a supplemental form of nitrogen must be added. For wastes totally
deficient in nitrogen this supplementation cost is normally comparable to that of
the air compressor power costs when the activated sludge process is the biological
treatment method used. Therefore, it is desirable in such cases to modify the operation of the activated sludge process to obtain minimum operational costs.
Chasick(l)has described a modification of the activated sludge process called
activated aeration. The process involved re-utilization of the excess activated
sludge solids wasted from the secondary settling tank of a conventional activated
sludge system. The object of this modification was to treat an additional sewage
flow and obtain greater BOD removal while economizing on the amount of oxygen
required. It was first used in New York to treat domestic sewage having a low
BOD. The effluent was of intermediate quality and suitable for the local conditions. The excess sludge wasted from the conventional activated sludge process is
active and still capable of utilizing organic matter. In the activated aeration
process, advantage is taken of this capacity of the waste sludge to remove organic
material on a one-pass no-recycle basis. The waste sludge is transferred to another aeration tank called an activated aerator into which the remaining portion of
the primary effluent is admitted. Chasick's data showed that the MLSS concentration was very low in the activated aeration tank (75 mg/l). The contents were
aerated for two hrs and allowed to settle. There was good synthesis and the final
MLSS concentration was 225 mg/l. The sludge from this process was wasted. The
BOD removal was 70 to 75 per cent. The flow diagram in this present study, shown
in Figure 1, is the same as that of activated aeration except for the nitrogen supplementation. However, the objectives desired from its application differ considerably. First, it is proporsed for nitrogen deficient wastes, not domestic sewage,
and second, high BOD removal requirements, instead of intermediate treatment,
are desired.
Wuhrman (2) while working with glucose acclimated sludge, subjected the
bacterial cells,  which were previously washed in phosphate buffer to remove ex-
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