Some Effects of High Salt
Concentrations on Activated Sludge
D. F. KINCANNON, Bioengineering Fellow
A. F. GAUDY, JR., Professor and Director
Bioengineering Laboratories
School of Civil Engineering
Oklahoma State University
Stillwater, Oklahoma
INTRODUCTION
Many factors contribute to the recent interest in the treatment of organic
wastes in saline waters. Wastes of high salt concentration arise from the manufacture of cheese and from pickle processing. Waters containing high concentrations of salt wasted from softening plants may at times be found in streams containing organic pollutants. Shipboard wastes contain high concentrations of salt.
Also, in many areas, natural surface waters are highly saline. As the water supply
becomes more critical, such water may be used in increasing amounts for certain
industrial needs. If, in turn, these waters become contaminated with organic
materials, the biological treatment which may be necessary could be affected by
the presence of salt.
The effects of sodium chloride on bacteria have been subject to investigation
in the microbiological field. Ingram (1,2,3) found that the endogenous respiration rate of Bacillus cereuswas increased by sodium chloride concentrations up to
0.2 M, but was decreased above this concentration. Winslow and Haywood (4)
found that the growth of Escherichia coli was stimulated at sodium chloride concentrations of 0.005 M to 0.25 M. Adaptation of Escherichia coli to sodium
chloride was studied by Doudoroff (5). It was found that cells exhibited the
greatest degree of adaptability to salt in the early stationary phase of growth.
Very young cultures (log-growth phase) and older cultures harvested some time
after reaching the stationary phase exhibited a lower degree of adaptability.
In the pollution control field Lawton and Eggert(6) have studied the effects
of salt on trickling filter slimes. They observed negative reduction in BOD when
salt concentrations greater than 20,000 mg/1 were applied or when slimes which
had become acclimated to salt concentrations greater than 20,000 mg/1 were
subjected to salt-free wastes. Stewart, Ludwig, and Kearns(7) have studied the
effect of salts on the extended aeration process and the applicability of this process for the treatment of shipboard wastes. Temporary reductions in treatment efficiency were noted when abnormally severe changes in salinity were combined
with heavy hydraulic and organic loadings. It was found that the sludge concentration in the aerator decreased when salt water (ocean water) was replaced by
fresh water.
Ludzack and Noran (8) have investigated effects of salt concentrations up to
20,000 mg/1 on the activated sludge process. It was found that increasing salt
concentrations stimulated oxygen uptake. In general, high salt concentration led
to decreases in flocculation and oxygen demand removal efficiency. Nitrification
was also severely curtailed.
In a previously reported study of batch activated sludge, Kincannon and
Gaudy (9) found that high salt concentrations could cause a severe decrease in
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