Stabilization of Refinery Waste
Waters with the Activated Sludge Process:
Determination of Design Parameters
RONALD L. DICKENSON, Process Engineer
JOHN T. GIBONEY, Chemical Engineer
Shell Development Company
Emeryville, California
INTRODUCTION
Ever increasing economic expansion and a growing concern for the quality of
the environment are making it necessary for industry to use more efficient waste
water treating techniques. Biological treatment, long used for treating domestic waste
but employed relatively recently by the process industries, is one of the most
important of the so-called secondary treatment processes which will give the
necessary increase in treatment efficiency. Probably the most efficient and widely
used biological technique for treating large volumes of waste water is the activated
sludge process.
Shell's first biological waste water treating plant, which included both a
trickling filter and an activated sludge unit, was installed at the Anacortes refinery in
the State of Washington in 1955. Since then trickling filters have been installed at
other refinery locations. The combination of expanded refinery and chemical plant
production coupled with more restrictive regulations to ensure the quality of the
receiving waters have led Shell to consider the activated sludge process in some of
their current effluent treater expansion programs.
In this paper we discuss the experimental development of parameters used in
the design of two commercial scale activated sludge systems for the stabilization of
petroleum refinery waste water. This work was conducted at Shell Development
Company's Research Center in Emeryville, California.
DESIGN PARAMETERS
In order to design a commercial-scale activated sludge plant (unless otherwise
noted, the term "activated sludge" will mean a continuous completely mixed
activated sludge system) it is necessary to develop quantitative information about the
parameters influencing or controlling the biological system. The parameters discussed
in this paper are: 1) Substrate removal rate; 2) Oxygen utilization rate; 3) Oxygen
mass transfer efficiency; and 4) Sludge production rate.
These parameters are the most important ones in determining the size of the
basin, the amount of aeration capacity necessary and the amount of waste solids that
must be handled. There are other parameters which are important to adequately
design an activated sludge treatment system such as biological nutrient requirements,
liquid-solid separation characteristics and the stability of the biota to a variety of
shock loads (transients). While these items were investigated in the course of our
experimental program they will be discussed only where they apply to evaluation of
the four primary parameters listed.
-294-