Bioxidation of Oil Refinery Wastewater Does Work.
Part II — Edmonton Refinery
W. K. ROSS, Coordinator of Environmental Control
Imperial Oil Enterprises, Ltd.
Edmonton, Canada
INTRODUCTION
The North Saskatchewan River emerges from the Rocky Mountains and flows
through the City of Edmonton. Its waters continue across the Prairies until they reach
Hudson's Bay. Towns and villages along the route use it for drinking water. It is inhabited
by a variety of life including water fowl and fish such as Northern Pike and Pickerel.
Rapid growth of industry and population in Edmonton has meant the quality of both
municipal and industrial effluents has had to be improved to preserve the quality of the
river.
Edmonton Refinery is located on the North Saskatchewan River immediately
downstream from the city. It has a capacity of 40,000 barrels per day of crude oil and
synthetic crude from tar sands. Its processes include crude distillation, powerforming,
catalytic cracking, alkylation and manufacture of lubricating oils and asphalt. It receives its
water and discharges its effluent into the river.
The refinery employed various techniques of effluent quality control in the past, such
as segregation of noxious wastes and disposal in a deep well and oil and solids removal in an
API separator. However, the needs of the future required further processing of the effluent
and a new system was designed and built.
The new process is probably older than the river itself. In any stream, quiet pools allow
dirt to settle to the bottom. Rapids and falls mix and oxygenate the cleared water providing
conditions where microorganisms in the stream consume any organic matter present.
Further settling in pools downstream produces clear, sweet water.
The first step in applying this biological treatment to the refinery effluent was to
identify quantities and types of pollutants and eliminate materials that would be harmful to
microorganisms.
High concentrations of oil can coat microorganisms and float them to the surface,
making them ineffective. Steps were taken to reduce oil in effluent from an average of 21
mg/1 in 1967/ 68 to 7.2 mg/1 in 1971, which was less than half the provincial allowable into
the river. These steps included changes in the method of neutralizing waste hydrofluoric
acid to eliminate the production of calcium fluoride, which tends to become oil soaked and
carry through the separator.
(Waste hydrofluoric acid is traditionally treated by adding lime, which produces
calcium fluoride, a solid. Instead of using lime, Imperial switched to caustic neutralization
with which it produces a sodium fluoride solution, which can then be injected into a deep
well.)
The separator mechanism was modified to reduce sludge carryover and reaction jet
baffles were installed in the separator inlet to reduce turbulence and short circuiting (by
which current flows rapidly along the bottom of the tank instead of evenly throughout the
vessel).
Most streams, such as spent caustic and sour waters, that would be toxic to
microorganisms were already being injected in the well. Surveys were made and remaining
toxic streams were handled the same way.
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