BIOKINETIC MODELS TO OPTIMIZE AERATED STABILIZATION
BASINS
Yogesh M. Mehta, Staff Manager
Ralph L. Stephenson, Senior Engineer
Brown & Root U.S.A., Inc.
Houston, Texas 77210
INTRODUCTION
Aerated Stabilization Basin (ASB) is a common and popular unit process for the treatment of
paper mill wastewater in North America. A situation already faced by several mills, and one which
can be anticipated to occur more frequently in the future, is the desire to upgrade effluent quality
as a result of raw waste load increases resulting from incremental production increases, without major
expenditures on the existing treatment facilities.
Numerous mathematical models are available to evaluate the performance of ASBs and for use
in predicting the performance of ASBs when operating and/or loading conditions are changed. The
dilemma is which model to use in making predictions of treated effluent quality and when investigating changes in operating conditions as all give slightly different results. What are the strengths
and weaknesses of the various models? This paper gives the results of the investigation of four different models as applied to three different ASBs and presents a discussion of the advantages and
disadvantages of each model.
DESCRIPTION OF THE MODELS
The four models that were analyzed are:
• Eckenfelder's Firsl Order Model |l|
• Lawrence & McCarty Model (2)
• The Exponential Model
• The NCAS1 Dynamic Model
The formulas for the first three of these models are shown in Table I. Formulas for the National
Council of the Paper Industry for Air and Stream Improvement Model (NCASI) were more extensive
and complex than can be presented in this paper, so the reader is referred to the literature [3,4,5].
The NCASI Model is based on Lawrence & McCarty's equations, but adds many more concepts to
these equations.
Table I. List of Design Formulas
Model
Equation for Effluent BOD
Equation for the Rate Constant
Eckenfelder
s,
s, =    	
1 + Kct
S, - Sr
Sct
Exponential
Sc = S,e<-K'''>
K'c = Irfe)
I
Lawrence & McCarty
Ks(l + bt)
S,    -
t(yk - b) - 1
(Ks + Sc)(bt + 1)
K = 	
Scyt
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