Interactions of Waste Feed, Activated
Sludge, and Oxygen, as Traced by
Radioactive Carbon
F. J. LUDZACK, Chemist
H. L. KRIEGER,   Chemist
and
M. G. ETTINGER,   Chief
Chemistry and Physics Section
Robert A. Taft Sanitary Engineering Center
Bureau of State Services
Public Health Service
Department of Health, Education, and Welfare
Cincinnati, Ohio
The respiration test is a useful tool to determine the biological oxidizability of a given waste, the suitability of a given inoculum for a specific
feed, or the effects of enviornmental changes. Respiration test data usually
are clear; however, interpretation of the data may be confused.
The nature of changes in an activated sludge after feeding has not been
clarified. It is difficult to select a suitable control or to evaluate the significance of the selected control. Feeding may be expected to produce a number of changes in an activated sludge:
1. Oxidative destruction or catabolism of historical cell material may
stop in favor of an anabolic or synthesis phase.
2. Part of the historical cell material may catabolize while a portion of
the population grows rapidly for a limited period.
3. Both anabolism and catabolism may be increased, thus increasing
oxidative destruction of the inoculum.
Pure culture studies suggest that these and other changes may occur. The
mixed biota of activated sludge complicates the problem because of population shifts due to natural selection (1).
Butterfield et al. (2) accepted the validity of an unfed control and the
concept that oxygen utilization of a fed mixture could be separated into additive fractions, one due to feed, the other to the inoculum. Ruchhoft et al.
(3) reported that oxygen utilization of a fed sludge was not strictly proportional to the feed oxygen demand; they reported that 30 to 70 per cent of the
oxygen use was associated with sludge storage components. Wooldridge and
Standfast (4) likewise recognized the contribution of inoculum storage products
in some of the earliest reported uses ofmanometic technique in sanitary engineering. They washed the sludge to reduce carry-over due to storage. This
practice is still popular, although the technique reduces the applicability of
such tests for plant scale application. Ruchhoft (3) and Bloodgood (5) tested
the sludge as sampled before and after feeding.
Porges,   et al.   (6) observed that about 37 per cent of the COD of milk
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