Aeration as a Partial Treatment
for Dairy Wastes*
SAM   R.   HOOVER,   JANET  B.   PEPINSKY
LENORE   JASEWICZ   AND   NANDOR  PORGES
Eastern Regional Research Laboratory**
Philadelphia 18, Pa.
Previous reports have been made on laboratory studies on aerobic
oxidation of a simulated dairy waste (0.1 per cent skim milk solids)
in a continuous flow system2. The maximum rate of loading for
steady-state operation was 10 per cent of the volume an hour. A com¬
plete solids balance showed that 50 per cent of the milk solids was
assimilated into cell tissue or sludge; the remaining 50 per cent was
oxidized to C02 and water to gain energy for this assimilation. These
results were confirmed and extended by manometric measurements of
the rate and extent of oxidation of milk solids by activated sludge1.
This rapid aeration process with a centrifugal separation of the
bacterial cells was proposed as a possible system for treating dairy wastes
in industry.
The pattern of operation in dairies is such that a large proportion of
the waste is produced in a few hours in the morning, with almost none
between 5 p.m. and early morning. Therefore, experiments with a
fill-and-draw system which could take advantage of this intermittent
production of waste have been made. The reductions in B.O.D. were
such that discharge of the total effluent might be considered when com¬
plete treatment of the effluent is not required. Furthermore, the effluent
would be relatively stable and could be treated satisfactorily in a
municipal sewage system.
EXPERIMENTAL
The laboratory equipment employed was a Humfeld aerator main¬
tained at 30° C. (86° F.) as previously described2. A drain was
inserted so that all but 2.4 L., 20 per cent of the total capacity, would
be removed. The simulated waste was added in four hours; 9.6 L.
were added daily.   C.O.D. analyses3 were made approximately hourly;
* Report of a study made under the Research  and Marketing Act of 1946.
** One   of   the   laboratories   of   the Bureau  of   Agricultural  and  Industrial
Chemistry,   Agricultural   Research Administration,   U.   S.   Department   of
Agriculture.
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