Section 7. PAINT, INK, AND DYE WASTES
BIOLOGICAL TREATMENT OF PHENOLIC PAINT-STRIPPING
WASTEWATER
Capt. Jack H. Jeter, Research Environmental Engineer
HQ Air Force Engineering and Services Center
Tyndall Air Force Base, Florida
INTRODUCTION
Paint-stripping operations for control of corrosion on aircraft are performed at practically all Air
Force bases. There are primarily two operations used for stripping the aircraft, spray operations and
dip tank operations. Aircraft parts are either sprayed with the paint stripper, or dipped into large
tanks containing stripper. The parts are then rinsed with large quantities of water. Both of these
operations generate large quantities of wastewater with high concentrations of organic pollutants.
Between 20,000 and 200,000 gallons of stripper laden wastewater are generated for each aircraft
stripped [1].
The coatings used on aircraft are required to be very resistant to abrasion, and are therefore very
hard to remove. They usually consist of the epoxy primers with polyurethane topcoats. These coatings
are very resistant to chemical strippers and require the most aggressive strippers. Strippers with 20%
phenol as the active ingredient are the most effective on these epoxy/polyurethane coatings. An additive of considerable environmental concern in the stripper solution is hexavalent chromium. The
resultant wastewater, high in phenol and chromium due to the chemical stripper, is further contaminated by the chromate constituents in the paints, i.e., zinc chromate and strontium chromate.
The Air Force has centralized the large paint-stripping and other industrial operations into Air
Logistics Centers (ALC). The paint-stripping operations are performed intermittently. The treatment
of the wastewaters generated on these ALC's is a problem due to a number of factors: the variability
of the flow rates from the stripping facilities, the variation in the concentrations of the toxic organic
components, and the toxic or inhibitory action of the phenolic compounds.
The purpose of this paper is to describe a method developed for biological treatment of paint-
stripping wastewaters.
AIR FORCE OFFICE OF SCIENTIFIC RESEARCH/TRINITY UNIVERSITY PROJECT, "AN
ECOLOGICAL APPROACH TO THE PROBLEM OF BIODEGRADATION OF PHENOLIC
WASTES"
Under a grant from the Air Force, Trinity University in San Antonio, Texas studied the population ecology and stability of microorganisms involved in the biodegradation of phenolic compounds. In the early 70's the paint strippers most commonly used by the military consisted of
approximately 53% dichlorobenzene, 25% cresol, and 22% paraffin, etc. The purpose of this research
was to investigate the reasons for the failure of biological treatment plants which receive phenolic
paint stripping wastewater.
The investigators obtained organisms from the paint-stripping facility in San Antonio in areas
exposed to the paint-stripping wastewater. Organisms were also collected from the waste treatment
trickling filter. The cresol-degrading organisms were isolated on agar plates of mineral salts media
with 900 mg/1 cresol as the sole carbon and energy source. The organisms initially isolated included
Pseudomonas aeruginosa, P. fluorescens, and P. putida. The isolated cresol degraders were grown
in synthetic wastewater, liquid mineral salts media containing 900 mg/1 cresol, and seeded onto a
glass column, 6 inch diameter and 9 feet tall, containing a ceramic saddle packing medium. The
organisms rapidly colonized the packing medium.
The experimental parameters investigated for their effect on cresol utilization included temper-
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