Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Civil Engineering


The use of stabilization ponds as a means of providing wastewater treatment has been a common practice in many small midwestern communities. However, because of more stringent water quality standards and increased loadings on existing facilities, many communities have been forced to seek improved methods of wastewater treatment. One method of increasing the capacity of an existing stabilization pond is the addition of an aerated lagoon. In general, an aerated lagoon may be defined as a basin with a liquid depth of 6 to 15 feet in which oxygen is supplied to the liquid contents by mechanical or diffused aeration equipment and by induced surface aeration. Aerated lagoons can be classified into two major categories: completely mixed aerated lagoons (CMAL); and facultative aerated lagoons (FAL). The major difference between the two is the degree of mixing present in the system. The degree of mixing and dissolved oxygen concentration in a FAL is lower than that in a CMAL. Also, a certain amount of the suspended solids settle to the bottom of the FAL and decompose by benthal oxidation and anaerobic decomposition. These major differences between the CMAL and FAL often result in different treated effluent strengths which are dependent on the proportionate amount of dissolved and suspended solids in the effluent. Therefore, to evaluate lagoon performance, it is desirable to know the degree of mixing present within the system. Classification of a lagoon as either a CMAL or a FAL is difficult because of variables such as the power-input-to-volume ratio, basin geometry, and type of aeration equipment all of which influence the degree of mixing present. Usually a completely-mixed system will produce a more consistent effluent quality than a facultative system; but the power cost to maintain a completely-mixed system .is generally higher. The objective of this study was to evaluate and compare the degree of mixing present in a system operated at different mixing speeds. Dye tracer techniques were employed to accomplish this objective.

Library of Congress Subject Headings

Factory and trade waste

Refused and refuse disposal

Sewage lagoons

South Dakota State University Theses



Number of Pages



South Dakota State University