45    TWO-STAGE CYCLIC, AEROBIC TREATMENT OF
CONTAMINATED GROUNDWATER
Cheng-Hsiung Hsu, Graduate Research Assistant
James C. Young, Kappe Professor of Environmental Engineering
Jean-Marc Bollag, Professor of Soil Microbiology
Center for Bioremediation and Detoxification
The Pennsylvania State University
University Park, Pennsylvania 16802
INTRODUCTION
Evidence of groundwater contamination has been reported at Reilly Industries, Inc. in Indianapolis, Indiana, where alkylpyridines and other chemicals have been produced as industrial products.1
The major contaminants detected at the Reilly site include monosubstituted pyridines, such as 2-
picoline, 3-picoline, 4-picoline, and di-substituted pyridines, such as 2,3-lutidine, 2,4-lutidine, 2,5-
lutidine, 2,6-lutidine and 3,5-lutidine, plus acetic, propionic and butyric acids. Alkylpyridines are
relatively water soluble and thus have a high potential for environmental mobility. They are also
associated with undesirable taste and odor at concentrations below 1 mg/L.
A suggested permissible concentration of 35 /ig/L for individual pyridine derivatives has been
established for recharge to the aquifer in the Record of Decision (ROD)2 for the Reilly site. Such low
concentrations generally can be obtained in biological treatment processes only by maintaining the
degradation reaction in a decay environment. Decay occurs when a biological process is operated at an
extremely high biomass to substrate ratio. This condition may also be beneficial in minimizing sludge
production.
The decay concept has been used by Howerton and Young3 to develop a two-stage, cyclic anaerobic
filter to improve COD removal over that which is possible in a conventional anaerobic filter. This
process operates in a conventional two-stage mode in such a manner that high rates of growth occur in
the first stage and decay conditions exist in the second stage. Periodically, the two stages are reversed,
or cycled, so that the former growth reactor is transferred into a decay reactor and the previous decay
reactor enters a growth mode. Compared to a single-stage unit, the cyclic mode of operation has been
shown to produce lower residual soluble chemical oxygen demand (SCOD) than a mixed process
operating at the same hydraulic retention time and organic loading. Besides this fact, two-stage, cyclic
reactors also have been shown to be capable of tolerating extreme shock loads while still maintaining a
high removal efficiency. Little sludge wasting has been required for full scale two-stage cyclic anaerobic filters for the treatment of industrial waste.4,5
The purpose of the study described in this paper was to use a fixed-film aerobic packed-bed reactor
to treat a water formulated to simulate the groundwater at the Reilly site. The specific objectives were
to examine how the operation of a two-stage, cyclic, fixed-film, aerobic reactor can improve system
efficiency and reduce solids production, and to evaluate how each reactor (lead and follow) in the
cyclic operation affects the removal efficiency of alkylpyridines and organic acids. Single and two-
stage cyclic completely mixed reactors were operated simultaneously with the packed-bed reactors to
provide a basis of comparison.
BACKGROUND
Decay Reactions in Biological Treatment Processes
In biological treatment processes, microorganisms derive energy for cell synthesis from the soluble
organic matter during the process of metabolism. If substrates are not available in amounts sufficient
to support growth, the microorganisms enter a starvation mode during which the synthesized biomass
decays through the process of endogenous respiration or cell lysis. Biomass transformation by decay
reactions can be expressed as follows:
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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