OPTIMIZATION AND CONTROL OF THE
ACTIVATED SLUDGE TREATMENT PROCESS BY
QUASICONTINUOUS OPERATION:
CONCEPT, STRATEGY AND RESULTS
Rainer Staud, Research Associate
Peter A. Wilderer, Professor
Ludwig Hartmann. Professor
Universitat Karlsruhe
Karlsruhe, Federal Republic of Germany
Optimization of the activated sludge treatment process has been of concern since Ardern
and Lockett [1] introduced this treatment method in 1914. In the attempt to achieve the
required treatment effect reliably and economically various process modifications have
been developed. The mechanisms involved have been studied in detail, and mathematical
formulations have been designed to describe the reactions taking place. In addition, emphasis
has been placed on the improvement of technological system elements such as aerators. But,
despite all these activities, in practice a real breakthrough has not yet been achieved. Process
designers and operators still depend extensively on empirically gained experiences, and
process optimization is more or less restricted to oxygenation control and troubleshooting.
Difficulties in the application of scientifically based concepts for process optimization
are:
1. The biomass employed is not static and uniform in character but heterogeneous. Biological
wastewater treatment deals with site-specific biocommunities characterized by biological
and physical properties which are the result of the environmental conditions in effect at the
particular location. Important environmental factors are influent loading, composition and
nutritive quality of the wastewater ingredients, reactor system, and reactor design.
2. The wastewater characteristics are also not uniform but fluctuate according to the diurnal,
weekly and seasonal rhythm of the activities of population and industry in the catchment
area of the particular treatment plant.
3. Coordination of the treatment process with the variations of the influent characteristics is
needed but rarely accomplished. It would require an adequate monitoring system as well as
an adequate process control strategy. The development of these prerequisites is just at its
beginning [2].
As far as fluctuations of the influent loading, and resulting effects on process efficiency
are concerned, process optimization can be achieved by either diminishing frequency and
amplitude of the influent parameter variation or by damping the process related effects of
those variations.
The purpose of this chapter is to introduce a technique which emphasizes the adjustment
of a continuously operated activated sludge treatment system to fluctuating influent loading.
The implication of this concept, the methods developed to accomplish this technique,
and results of a full-scale study will be discussed.
BASIC CONSIDERATIONS
Activated sludge is biologically characterized by a specific organism-type distribution
which is maintained by the food supply provided, and which determines the metabolic
capacity of the biocommunity, the capacity to metabolize specific types of substrates such
as soluble organics, organic particles or ammonia [3].
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