Establishing the basis for a wastewater treatment plant design

Autor: Earnest F. Gloyna

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This paper presents basic concepts that must be considered if a biological system is chosen to stabilize organic pollutants commonly found in many industrial wastewaters. The important equations describing the kinetics of a microbial process are presented, the basic design concepts of aerobic, anaerobic and facultative biological systems are discussed. To establish a sequential approach to conceiving, designing, constructing, operating and maintaining a wastewater treatment plant, it is necessary to thoroughly characterize the waste. These treatability data are needed to provide a definition of the wastewater in terms of meaningful design parameters. Basic design criteria can best be formulated from bench or pilot-scale studies. It is much more economical to explore the many technical variables in well-established test programs than it is to modify full-scale operations. Worldwide emphasis on environmental preservation, human health, food and conservation has placed increased emphasis on wastewater treatment. Human wastes and pollution resulting from man’s need for material things continue to accumulate at an alarming rate and now seriously impact on the usability of diminishing available resources. Since the elimination of wastes at the source is not always practicable, it is therefore necessary that human and industrial wastes be treated before release to the environment to the extent required. Frequently, the most cost effective treatment method available for stabilizing organic pollutants involves an engineering adaptation of natural occurring biological processes. This paper will focus on an analysis of the microbial processes for waste stabilization. The processes of microbial growth and energy utilization are similar under most wastewater treatment concepts, although bacteria function differently under anaerobic, facultative or aerobic environments. With known technology, it is possible to develop mathematical expressions which describe the basic parameters of biological waste treatment processes. Furthermore, much can be gained from transferring knowledge from one treatment process and using this information to guide, design and operate significantly different processes. A unifying parameter such as biological solids can be related to microbial growth, substrate assimilation and process efficiency. For example, the parameter such as sludge age in highly mechanized aerobic systems is synonymous to hydraulic detention time in less complex systems such as facultative waste stabilization ponds or even more sensitive operations typical of anaerobic digesters.

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