47    BIOLOGICAL TREATMENT OF NATURAL GAS PLANT
WASTEWATER
Neil J. Ferrell, Project Manager
Ford Bacon & Davis Technologies
Salt Lake City, Utah 84158
James C. Young, Kappe Professor of Environmental Engineering
The Pennsylvania State University
University Park, Pennsylvania 16802
BACKGROUND
Northwest Pipeline Company's natural gas processing plant at Opal, Wyoming, processes approximately 550 million cubic feet of natural gas per day. The plant extracts liquids generated by the
production of natural gas and processes the liquids into marketable products, primarily propane,
butane, ethane, and natural gasoline. The wastewater produced at this plant is composed of product
water, plant washdown water, and boiler blowdown and contains significant quantities of iron sulfide.
The product water is extracted from the natural gas and liquid hydrocarbons and is laced with various
hydrocarbon fractions. Liquid hydrocarbons and wastewater are collected into a flare sump at the
lower end of the plant site. Since construction of the plant in the late 1950"s, the light hydrocarbon
fractions have been decanted from the flare sump, and the residual heavier fractions and water have
been discharged into an evaporation pond.
Northwest Pipeline Company plans to close the wastewater pond at the plant site during 1993.
Therefore, the wastewater collected from the processing plant must be handled and/or treated by an
alternate method of disposal. A contract was established between the town of Opal and Northwest
Pipeline Company to allow the use of two existing sewage lagoons as evaporation ponds for the
Company wastewater. Use of these lagoons requires that the wastewater be treated to the standards set
for their operation by governmental regulations. Specifically, this requires a plant effluent Chemical
Oxygen Demand (COD) below 300 mg/L and a Biochemical Oxygen Demand (BOD5) less than 250
mg/L plus control of heavy metals, salts, total dissolved solids, halogenated volatile organics, benzene, ethylbenzene, toluene, total xylenes, and total petroleum hydrocarbons.
WASTEWATER CHARACTERISTICS
Anticipating these requirements, the Company initiated a wastewater characterization study in
March of 1990. This study identified the need for pretreatment of the wastewater to remove oils and
other hydrocarbons and to remove iron sulfide that would be toxic or otherwise interfere with most
types of biotreatment. Additional analysis of the wastewater after pretreatment was conducted by an
independent laboratory over a six month period to further characterize the wastewater quality. The
following characterization (major elements only are shown) was established for treatment plant
design.
Flow Rate
8,640-21,600  gpd
pH
9-9.5   pH units
TDS (total dissolved solids)
3,000-7,000  mg/L
BOD5 (biochemical oxygen demand)
8,000-21,500  mg/L
COD (chemical oxygen demand)
10,000-29,300  mg/L
Benzene
4-9.4  mg/L
Toluene
6-17  mg/L
Ethylene glycol
100-200  mg/L
Methanol
4,000-18,000  mg/L
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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