ABSTRACT
Wastewater treatment is designed to use the natural purification processes (self-purification processes of streams and rivers) to the maximum level possible. It is also designed to complete these processes in a controlled environment rather than over many miles of stream or river. Moreover, the treatment plant is also designed to remove other contaminants that are not normally subjected to the natural processes as well as treating the solids that are generated through the treatment unit steps. The typical wastewater treatment plant is designed to achieve many different purposes:
• protect public health • protect public water supplies • protect aquatic life • preserve the best uses of the waters • protect adjacent lands
Wastewater treatment is a series of steps. Each of the steps can be accomplished using one or more treatment processes or types of equipment. The major categories of treatment steps are
• Preliminary Treatment-removes materials that could damage plant equipment or would occupy treatment capacity without being treated
• Primary Treatment-removes settleable and flotable solids (may not be present in all treatment plants)
• Secondary Treatment-removes BOD5 and dissolved and colloidal suspended organic matter by biological action; organics are converted to stable solids, carbon dioxide, and more organisms
• Disinfection-removes microorganisms to eliminate or reduce the possibility of disease when the flow is discharged
• Sludge Treatment-stabilizes the solids removed from the wastewater during treatment, inactivates pathogenic organisms, and/or reduces the volume of the sludge by removing water
The various treatment processes described above are discussed in detail later in the handbook. Because wastewater operators are expected to have a well-rounded knowledge not only of
treatment unit processes but also of the substance (the wastestream) they are treating, in this chapter, we describe the sources and various characteristics of the wastestream they treat.
