58    APPLICATION OF A PROCESS MODEL CALIBRATED WITH
RESPIROMETRY TO PREDICT FULL-SCALE
ACTIVATED SLUDGE PERFORMANCE
Richard J. Colvin, Project Engineer
Alan F. Rozich, President
Bioprocess Engineering, Inc.
Wilmington, DE 19808
Anthony F. Gaudy, Jr., Chairprofessor of Civil Engineering
University of Delaware
Newark, DE 19716
John Martin, Operations Engineer
City of Baltimore
Baltimore, MD 21202
INTRODUCTION
Biological systems, such as activated sludge, often comprise the backbone of the process technology
which is utilized for treating municipal and industrial wastewaters. With the increasing regulatory
constraints and requirements that pollution control managers must face, activated sludge systems in
both the public and private sectors will be expected to deliver better effluent quality on a more
consistent basis. This will require a control strategy which can react to variations in influent waste
characteristics such as changes in waste components, in strength of the waste, or in flow rate. Also,
pollution control professionals need to be increasingly concerned with controlling the levels of toxicity
and organics in effluent streams. Toxic components of influent waste must be considered from two
viewpoints: 1) their effect on the treatment process and its primary function, removal of the influent
COD; and 2) pass-through of toxic materials into the plant effluent.
As is the case with any process, in order to realize optimal performance, it is necessary to utilize
process control models for delineating guidelines for both design and operation. Although several
models1,2,3-4 are available for designing fluidized biological processes such as activated sludge, it is
rare for these models to be utilized for making specific recommendations for operation or to be used
on a frequent basis as a predictive tool by plant management. Part of the reason for this may be the
fact that some of the models are primarily suited for use in design. However, another explanation for
this is the fact that it is difficult and time-consuming to evaluate the biological constants that must be
inserted into the process control models to make them applicable for a particular treatment situation.
This paper describes the application of a respirometric protocol that enables practitioners to determine specific operating strategies which are based on character and strength of the influent wastewater and on the biodegradation capability of the plant biomass. The procedure utilizes a proven
process control model which is calibrated using biodegradation measurements made with an electrolytic respirometer. Data collection as well as process analysis are computerized and coordinated via a
software package. A series of verification studies indicate that the protocol accurately predicts process
performance for a full scale activated sludge treatment plant.
BACKGROUND
Process Control Models
Most process control models for activated sludge systems are based on the fact that net specific
microbial growth rate , nn, (reciprocal of 6\.) can be described as a function of the concentration, S, of
exogenous waste, or substrate. Since engineering controls can be applied to control /.„, and if the
relationship between p. and S is defined, then it is feasible to use the model to select the values of these
controls that are needed to maintain effluent quality, S. An example of such a predictive modelling
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
501