ORGANIC DEGRADATION BY BIOLOGICAL TREATMENT
OF HYPERSALINE WASTEWATERS
J. K. Petros, Research Scientist
E. M. Davis, Associate Professor
School of Public Health
University of Texas at Houston
Houston, Texas 77025
INTRODUCTION
In addition to the intended products and representative waste streams, certain industrial manufacturing processes generate hypersaline wastewaters containing various levels
of organic contaminants.   Yet within specified production areas, each hypersaline wastewater may remain relatively constant with regard to its salt content.   Biological treatment
of those waste streams by conventional treatment processes is therefore difficult, if not
impossible in many cases, due to the hypertonic nature of the aqueous system.   This paper describes an approach which was investigated for the biological degradation of organic materials in selected wastewater streams containing greater than 3.5% salt and the
maximum reductions which were attainable by bench-scale activated sludge units.
EXPERIMENTAL METHODS AND RESULTS
Three different approaches were taken during this investigation. They were: (a) isolation and/or identification of bacterial species capable of living in highly saline aqueous
systems; (b) acclimation of the selected salt-tolerant bacteria to three different hypertonic
waste streams; and (c) quantification of conventional activated sludge processes for treatment of those hypertonic industrial wastewaters in the proportions in which they would
occur in an actual process. Salt levels encountered in the wastewaters during the course
of this investigation ranged from 3.5% to 12% sodium chloride.
Initially, single-species and heterogeneous-unit operation seed cultures were tested for
their ability to grow over a wide range of salt concentrations, utilizing ethylene glycol as
the sole carbon nutrient source.   The industrial seed cultures were obtained from existing
treatment units containing elevated salt concentrations.   The basal medium was identical
to that reported in a previous study of high-salt biological degradation [I]. Over the
course of 16 days, cultures were transferred onto an agar medium containing progressively larger concentrations of the hyper-saline wastewaters with simultaneous decreases in
the concentration of ethylene glycol.   Growth characteristics of four known species, six
salt water isolates and two industrial-unit operation seed cultures are presented in Table I.
These data suggest that the saline wastewater was not a preferred nutrient source.   Six of
the original 12 cultures showed an inhibited degree of growth, while the remaining six
cultures failed to demonstrate adequate growth.   Since the incubation time was only
96 hr per each of the four series, bacterial cultures may not have had sufficient time to
completely acclimate to the carbon nutrient sources or the high salt levels.
Further testing was undertaken to evaluate growth characteristics of those bacterial
cultures which appeared to have been most reliable in tolerating high and variable salt
levels.   A salt-tolerance study was done on the medium recommended for culturing hydrocarbon degrading marine bacteria [2] with salt levels ranging from 5% to 12% sodium
chloride.   Duplication was accomplished at room temperature (25 ± 1 C) and at 35 C.
This experiment had an incubation period of 35 days and used dextrose (a-d-glucose) as
the sole carbon source.   From this series of tests, two salt-tolerant cultures grew well at
12% salt levels and were selected to be used in subsequent bench-scale batch-unit studies.
Those two species were Bacterium T-52 (ATCC #27042) and an isolate from Great Salt
Lake (Utah).
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