The Effect of Rate of
Mixing on the Deoxygenation of
Polluted Waters*
D. LORDI, Research Assistant
and
H. HEUKELEKIAN, Chairman, Department of Sanitation
Rutgers, the State University
New Brunswick, New Jersey
The oxygen-sag concept of Streeter and Phelps (11) shows that two
important processes are involved when pollutional material is discharged into
a stream. The de-oxygenation reaction and the re-aeration process, occurring
simultaneously, contribute to the oxygen balance resulting in an oxygen-sag
curve. Numerous studies have been made to define the re-aeration process
occurring in streams. Many of the factors influencing the oxidation of organic
material have been studied.
It appears that in shallow turbulent streams the rates of de-oxygenation of
polluted waters tend to be higher than the rates established in deep sluggish
rivers (1,5, 9). Differences have also been noted between the observed values
of de-oxygenation as determined under actual stream conditions and those
values obtained in laboratory studies. The indications of higher rates of deoxygenation under turbulent conditions are derived mainly from field studies
in which a number of inseparable variables were present. Various factors such
as depth, velocity offlow, temperature, surface-volume ratios, biological
growths, could contribute to the observed rates of de-oxygenation in various
types of streams. In order to separate some of these factors an experimental
laboratory re-aeration and de-oxygenation unit was devised. The purpose of
this study was to determine whether rate of mixing had any influence upon the
biological oxidation occurring in polluted waters.
EXPERIMENTAL METHOD
The apparatus used in these studies was originally developed and built by
Rand (6). Domestic sewage from Highland, New Jersey, was used as the source
of pollution. After collection, the sewage was filtered through glass wool to
remove the coarser solids. The filtered sewage was then stored at four C while
the one-day BOD was determined by the standard dilution method (10). The
one-day BOD was used to estimate the dilution of sewage required to produce
a desired oxygen sag. Dilutions were made so that a sufficient quantity of
oxygen would be utilized but the dissolved oxygen concentration would not be
diminished below a level of one mg/1. The dilutions were made using de-
chlorinated tap water. The cylinders were filled with the sewage mixture to
a height of four ft two-in., equivalent to a volume of 20.5 Is.
Stirring of the cylinder contents was started at the desired rate of circulation.   Initial samples of the polluted water were taken from each cylinder and
'Paper of the Journal Series, New Jersey Agricultural Experiment Station,
Rutgers, the state university of New Jersey, department or sanitation, New
Brunswick, New Jersey.
- 530  -