Section Four
BIOLOGICAL SYSTEMS-B. AEROBIC
33    BIOREMEDIATION OF ETHANOL AND PETROLEUM
HYDROCARBON CONTAMINATED GROUNDWATER
USING A ROTATING BIOLOGICAL CONTACTOR
Carole L. Engelder, Research Engineer
Sharon A. Matson, Technician
Amoco Oil Company
Amoco Research Center
Naperville, Illinois 60566
INTRODUCTION
Historical tank and piping leakage of petroleum product and recent spills of fuel-grade ethanol
have triggered soil and groundwater remediation efforts at an Amoco Oil Company petroleum
products marketing terminal in the midwest. Over thirty-five monitoring wells and one pumped well
have been installed at the terminal by an engineering firm to determine the actual hydraulic capture
zone and aquifer drawdown of the pumped well, and map the free product thickness. Location of the
wells at the terminal are shown in Figure 1.
Currently the site is being remediated by pumping up to 200 gpm of the groundwater to a publicly-
owned treatment works (POTW) sewer at a cost of $1.40 per 1000 gal. This amounts to over $12,000
per month for the groundwater disposal. In addition, the groundwater discharge to the sewer is
limited to <   200 ppm ethanol and <   25 ppm total petroleum hydrocarbons (TPH).
Given the readily biodegradable nature of the ethanol and light petroleum products, biological
treatment was chosen for study of the site clean-up. One remediation scenario would be to remove the
ethanol and petroleum hydrocarbons from the pumped groundwater in above-ground treatment and
discharge the treated stream to surface waters or recharge on-site to the aquifer.
Objectives of this study were to determine bioremediation efficiencies during treatment of the
contaminated groundwater at the marketing terminal. Data acquired can also be applied indirectly to
in-situ bioremediation options.
BACKGROUND
To investigate biological remediation of the groundwater, an above-ground process called the
rotating biological contactor (RBC) was chosen. Also known as bio-disc or rotary disc, this technology utilizes an attached-growth of bacteria to degrade the organic contaminants in the groundwater.
Studying the removal using the "biofilm" can develop information for both full-scale above-ground
biotreatment methods, as well as in-situ bioremediation accomplished through soil-attached bacteria.
An RBC consists of circular sheets of media that revolve in groundwater pumped through a tank.
Microbial biofilm grows on the media and is alternately exposed to oxygen in the air and organics in
the water as the discs continuously rotate. The discs, mounted along a shaft, are typically divided by
baffles into stages to enhance plug-type flow. Biofilm processes have a number of advantages over
suspended growth biotreatment methods, such as activated sludge. The RBC does not require continual monitoring of the biomass and the subsequent adjusting of waste sludge and return sludge flows.
Biomass control in an RBC is not necessary.
The amount and type of microorganisms in the biomass develops naturally along the RBC staging
to best treat the available waste. Organic contaminants in the groundwater are gradually consumed as
the influent flows through the four RBC stages, with the majority of biodegradation occurring in the
first stage.
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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