The Decomposition of Aliphatic
Esters by Aerobic Microorganisms
W. D. LANGLEY, Engineering Research Associate
W.  B. DAVIS, Associate Professor and Head
P. A. RICHARDS, Captain, USAF
Environmental Engineering Division
Civil Engineering Department
Texas A&M University
College Station, Texas
INTRODUCTION
Based on its ability to resolve and quantitatively analyze the various components of a multi-component system, gas chromatography is a valuable analytical
technique for industrial wastewater characterization and treatment studies. Used
in conjunction with the hydrogen flame ionization detector and with proper selection of operating variables the technique is capable of precise analysis of volatile
organics in water solution at the part per million level without prior sample preparation. The technique and some of its applications to industrial wastes have
been thoroughly described by Baker (1, 2). It has been shown to be of practical
value in monitoring process waste streams and treatment plant operation at the
Union Carbide plant in Charleston, West Virginia (3, 4). Various workers have
applied the technique to the analysis of volatile fatty acids in digester sludge
(5.6).
In the authors' laboratories aqueous solution gas chromatography has been
found to be an effective analytical method for the elucidation of multi-component substrate removal by aerobic microorganisms (7, 8, 9,10). Correlation of gas
chromatography with Chemical Oxygen Demand removal (11) as well as with Biochemical Oxygen Demand (7) have shown the value of the method in interpreting
the characteristics of the COD and BOD removal curves and identifying refractory
compounds within the limitations of the technique.
In addition, to providing the means whereby individual removal rates may be
determined simultaneously, gas chromatography is also capable of detecting the
appearance of volatile intermediate compounds in the biochemical decomposition or transformation of the primary substrates. These products may appear in the
aqueous medium as the result of hydrolysis or oxidation. In some instances, short
lived reduction products have been noted (12). The fate of these secondary substrates in the system may also be determined.
In some of the early work with this method it was noted that n-butyl acetate
underwent rapid hydrolysis in the laboratory activated sludge reactors. As a hydrolysis product 1-butanol appeared in the aqueous phase and its removal was followed subsequent to the disappearance of the ester. Inasmuch as the hydrolysis
did not occur at neutral pH in the water solution alone, its occurrence in the microbial system was attributed to the presence of an esterase enzyme, the reaction
proceeding according to the following equation.
CH3COOC4H9 + H20 esterase»C4H9OH + CH3COOH
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