Effects of Contaminants on Reaeration
Rates in River Water
V. KOTHANDARAMAN, Assistant Scientist
Water Quality Section
Illinois State Water Survey
Peoria, Illinois
INTRODUCTION
There is a variety of operations in which air is dispersed into a liquid phase.
The function of air in a dispersed phase may be purely mechanical, as in the case of
air lifts, or physical as applied in air flotation. It is also used as a means of supplying
oxygen to the liquid phase as in bio-oxidation processes. The rate and therefore the
efficiency of oxygen transfer are important considerations in the design of aeration
equipment. Evaluation of the reaeration capabilities of water bodies receiving treated
or untreated wastes is an important aspect in estimating their waste assimilative
capacities.
Minute quantities of some organic and inorganic substances have been found to
affect the oxygen transfer rates. Effects of impurities like alkyl benzene sulfonates,
fullers earth, starch, alcohols, acids etc., added to tap or distilled water on the overall
oxygen transfer coefficient have been investigated. Extensive studies have been conducted to delineate the effects of domestic sewage and industrial wastes on oxygen
absorption efficiency. There has been a consensus among the investigators that the
surface active agents have a tendency to suppress the oxygen transfer rate and that
the extent to which it is affected depends on the characteristics and concentration of
synthetic detergent used and the method of aeration adopted. Thus, Lynch and
Sawyer (1) concluded that the addition of 50 mg/1 of anionic and non-ionic commercial detergents to tap water reduced the transfer coefficient value in tap water
from 94 to 33 per cent. Gameson, et al, (2), studying the effects of detergents in a
natural river system reported that the detrimental effects of anionic detergents are
more pronounced at lower mixing rates than at higher mixing rates. The results of
Downing and Truesdale (3) showed that the addition of 1 mg/1 of alkyl benzene
sulfonate to sea water as well as to tap water reduces significantly the oxygen
transfer coefficient. Similar conclusions were indicated in the studies of Holroyd and
Parker (4), Cullen and Davidson (5), and others.
Kehr (6) studying the effects of sewage on reaeration rates reported that the
addition of increasing percentages of sewage to tap water progressively reduced the
reaeration rate to an extent of 60 per cent. Contrary to the findings of Gameson, et
al (2), the results of Kehr indicate that the addition of even a low percentage of
sewage drastically reduces the reaeration rates with increasing velocities in an experimental channel. Kessner and Ribbius (7), comparing the differences in the effects of
sterilized sewage on oxygenation due to the methods of aeration came to the general
conclusion that aeration by means of compressed air is influenced far more unfavorably by sewage than with surface aeration by brush aerators.
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