32    HIGH TDS WASTEWATER TREATABILITY STUDY-
DESIGN CONSIDERATIONS
Enos L. Stover, President
Alan W. Obayashi, Director of Process Development
Stover & Associates, Inc.
Stillwater, Oklahoma 74076
INTRODUCTION
The applicability of biologically treating a particular wastewater is a function of the biological
degradability of the dissolved organics present in the wastewater. When considering the economics of
a biological treatment system, the time required to biologically degrade the dissolved organics is of
primary importance. The degradation rate of an organic compound is a function of the molecular
structure of the compound, the prevailing environmental conditions, the genera and species of microorganisms utilizing it as a food source, and the time required for microorganisms to develop the
enzymes necessary for substrate utilization.
The amenability or resistance of certain classifications of organic compounds to biological oxidation is well documented as follows:
1. Aliphatic or cyclic aliphatics are usually more susceptible to biological degradation than
aromatics.
2. Unsaturated aliphatics, such as acrylics, vinyl, and carbonyl compounds, are generally
biodegradable.
3. Molecular size is significant concerning the biodegradability of an organic. Polymeric
and complex molecular substances have shown resistance to biological degradation, part
of which is attributed to the inability of the necessary enzymes to approach and attack
susceptible bonds within the compound structure.
4. Structural isomerisms in organic compounds affect the relative biodegradability of
many compound classes. For example, primary and secondary alcohols are easily
degraded, while tertiary alcohols may be resistant.
5. The addition or removal of a functional group affects the biological oxidation. A
hydroxyl or amino substitution to a benzene ring renders the compound more degradable than the parent benzene, while a halogen substitution causes it to be less
biodegradable.
6. Many organic compounds are easily biodegraded at low concentrations, but are bio-
static or bio-toxic at higher concentrations.
Dissolved inorganic constituents can also affect the biological treatment processes. High levels of
dissolved inorganics (high TDS) can have significant negative impacts on the activated sludge process.
Some commonly observed problems include poor sludge settling characteristics, dispersed solids, and
more sensitivity to temperature changes and variability in organic loadings. High TDS wastewaters up
to 2% to 3% TDS can and are being successfully treated biologically. However, the variability in TDS
concentrations at these levels is a critical operational parameter, and extreme care must be used in
both adapting and acclimating the biological culture, as well as, taking extreme care to minimize the
variability of the TDS concentrations.
The results of high TDS wastewater biological treatability studies on a chemical plant wastewater
are discussed in this paper. Major considerations centered around biological treatment kinetics as
developed by Stover and Kincannon for defining treatment capabilities in the activated sludge process. Other factors included sludge settling, thickening and dewatering characteristics, along with
oxygen transfer considerations. Test results indicated activated sludge treatability to be feasible with
major consideration being the variability of TDS levels.
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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