Biochemical Oxidation of Dairy
Wastes. VII. Purification, Oxidation,
Synthesis and Storage
NANDOR   PORGES,   LENORE   JASEWICZ   AND   SAM   R.   HOOVER
Eastern Regional Research Laboratory
U. S. Department of Agriculture
Philadelphia, Pennsylvania
Oxidation and assimilation of waste by aerated sludge were emphasized in our studies summarized in a microbiological process report (20).
Aeration of a synthetic waste skim milk with sufficient agitation led
to two premises. First, there occurs a rapid assimilation and conversion
of the available C.O.D. into microbial cells or sludge. During this
period, 37.5% of the C.O.D. is completely oxidized to CO2 while
cell material is synthesized (10). Second, the cell material is subsequently oxidized during catabolism by endogenous respiration. Sludge
oxidation continues at the rate of 1% per hour (8) and higher according to pilot plant studies at Pennsylvania State University  (11).
Thus, with vigorous agitation and aeration, 1000 p.p.m. skim milk
solids were changed in 6 hours to additional 500 p.p.m. sludge solids
by the 500 p.p.m. sludge present as seed (20). Increasing sludge concentration reduces the time required for the first step. Such assimilation and oxidation were stoichiometrically represented by the following
hypothetical equation of synthesis:
8(CH20) + C8H12N203 + 6 02"> 2C5H7N02 +
6 C02 + 7 H20.
This equation shows that 8 moles of lactose carbon and 8 moles of
casein carbon required 6 moles of oxygen for conversion to microbial
cells with the formation of 6 moles of carbon dioxide. Respirometer
studies showed that lactose and casein are oxidized at the same rate
based on their oxygen demands (7).
In our studies it was more feasible to calculate the starting C.O.D.
from previously determined values for the sludge and synthetic wastes.
Analytical values for the mixtures gave apparent discrepancies that were
attributed to sampling techniques or to rapidity of oxidation. Later,
Kountz observed an almost instantaneous decrease in soluble C.O.D.
when dairy waste was mixed with sludge in his pilot plant investigations  (13).   Eckenfelder noted a similar occurrence and applied this
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