CONTROL TESTS AND KINETICS OF ACTIVATED SLUDGE PROCESS
Lawrence K. Wang, Assistant Professor
Department of Chemical and Environmental Engineering
Rensselaer Polytechnic Institute
Troy, New York 12181
Calvin P. C. Poon, Professor
Department of Civil and Environmental Engineering
University of Rhode Island
Kingston, Rhode Island 02881
Mu Hao Wang, Sanitary Engineer
New York State Department of Environmental Conservation
Albany, New York 12233
INTRODUCTION
Standard Methods for the Examination of Water and Wastewater [ 1 ] and the Manual
of Methods for Chemical Analysis of Water and Wastes [2] are often considered the Bible
of environmental engineers.   However, most test methods listed in the two publications
are for the determination of water and wastewater quality.   Only a few are general control tests.
There are many operational and control tests specifically developed for use in designing
and/or controlling the most common activated sludge process.  They are scattered in the
literature, not standardized yet by the academic and professional associations, but widely
used by the researchers and sewage treatment plant operators.  This article summarizes
the basic activated-sludge process kinetics and the related test procedures, clarifies some
academic disputes, and further presents several new control tests.
The process schemes included are:   (a) complete-mix reactor without sludge recycle;
(b) complete-mix reactor with sludge recycle; and (c) plug-flow reactor with sludge recycle.
The test methods presented are for the determination of:   biodegradability, oxygen uptake
rate, solids and residuals, sludge settling, depth of sludge blanket, sludge units, substrate
utilization rate, mean cell residence time and sludge age, net specific growth rate, sludge
production, volumetric loading, recirculation ratio, BOD/COD and BOD/TOC ratios,
ultimate BOD of microbial cells, effluent soluble BOD, oxygen requirements, treatment
efficiency, yield coefficient and endogenous respiration coefficient, growth parameter,
sludge volume index, sludge nitrifying ability, and sludge denitrifying ability.
It is believed that the compiled test procedures and basic kinetic models would provide researchers with a general base on which the full-scale treatment plants may be
designed or evaluated.   With them the sewage treatment plant operators can also conduct
the control tests correctly and, in turn, operate their plants efficiently.
BASIC KINETICS
The success of an activated sludge process in producing a high-quality effluent depends
on a continuous growth of biological floes having a good settling characteristic.   The
growth of biological floes is accompanied by the organic substrate removal.   The rate of
microbial growth and the rate of substrate utilization are interrelated.   If one assumes that
the Michaelis-Menten enzymatic kinetic can be applied to the substrate utilization by
microorganisms in the process, then
(dS/dt) kmS
X       " K, + S
501