40    DENITRIFICATION OF HIGH-STRENGTH INDUSTRIAL
WASTEWATERS
William W. Clarkson, Assistant Professor
Ben J. B. Ross, Graduate Research Assistant
Srikanth Krishnamachari, Graduate Research Assistant
School of Civil Engineering
Oklahoma State University
Stillwater, Oklahoma 74078
INTRODUCTION
Industries producing highly concentrated nitrogenous waste streams include chemical fertilizers,
munitions, nuclear fuel processing, and semi-conductor manufacturing, among others. Regenerant
streams from ion exchangers used to remove contaminants from drinking or process waters may also
present problems in treatment and disposal of strong nitrogenous wastes. Biological nitrification and
denitrification have been applied to tertiary treatment of low-strength municipal wastewaters, with
nitrogen concentrations typically < 50 mg/L. Limited studies have shown the potential of these
processes to treat nitrogen concentrations > 1,000 mg/L efficiently, particularly in the absence of
significant amounts of biodegradable organic matter.
Previous studies',2 have shown that fixed-biofilm reactors were capable of completely nitrifying
between 500 and 1,000 mg NH4-N/L in a semiconductor waste, providing an economically viable
alternative to air stripping. Denitrification could be used as a second stage process in a complete
removal system for wastes of this type, or alone for treatment of wastes containing nitrate and/or
nitrite-N. Denitrification may be carried out heterotrophically by common facultative bacteria, for
example species of Pseudomonas, Alcaligenes, Paracoccus, Bacillus, Propionibacterium, etc. These
organisms metabolize compounds for carbon and energy. Much less well-known are the various
autotrophic denitrifying bacteria. Different species are capable of deriving energy from oxidation of
hydrogen, reduced iron and sulfur ions, etc. for thee incorporation of inorganic carbon. Examples of
sulfur oxidizers are Thiosphaera pantotropha, Thiomicrospira denitrificans, and Thiobacillus denitri-
ficans3. Both heterotrophic and autotrophic denitrifying bacteria use nitrate as a terminal electron
acceptor to facilitate the oxidation of substrate. The intermediate and final products of this process
are given in the following general sequence from more oxidized to more reduced:
NO3-- N02—' NO"- N20--> N2
Certain species of bacteria may be more or less able to use each of the intermediates to oxidize
substrate. Environmental conditions may also affect how completely the reduction may be carried
out, resulting in accumulation of certain intermediate compounds.
Comparison of the stoichiometry of heterotrophic and autotrophic denitrification reveals that,
whereas the heterotrophs are net alkalinity producers, autotrophic denitrifiers consume alkalinity (are
net producers of acidity) in much the same way as nitrifying bacteria. Following are calculated
stoichiometrics for the two systems:
Autotrophic3:
NO5 + 0.79 S20 3 +0.27 HCOj + 0.20 H20 = 0.05 C5H7O2N + 0.47N2+ 1.56 SO J +0.28 H +
Heterotrophic4:
NOj + 1.08 CH3OH + H +  = 0.065 C5H702N + 0.47 N2 + 0.76 Co2 + 2.44 H20
The purpose of this study was to determine the upper concentration and loading rate limitations of
both heterotrophic denitrification using methanol as carbon and energy source, and autotrophic
denitrification using bicarbonate carbon and thiosulfate as electron donor. Studies were carried out in
bench-scale attached film expanded bed (AFEB) and upflow sludge blanket (USB) reactors. There-
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
347