Wastewater Sources And Characteristics

7.1 INTRODUCTION

This chapter describes individual pollutants and stressors that affect water quality. Knowledge of the parameters and characteristics most commonly associated with wastewater treatment processes is essential for the wastewater operator. Wastewater practitioners are encouraged to take a holistic approach to managing water quality problems.

It is important to point out that when this text refers to water quality, the definition used is predicated on the intended use of the water or treated wastewater. Many parameters have evolved that qualitatively reflect the impact that various contaminants (impurities) have on selected water uses; the following sections provide a brief discussion of these parameters.

It is also important to point out that wastewater treatment is designed to use the natural purification processes (self-purification processes of streams and rivers) to the maximum extent possible. In fact, we can say that the unit processes that make up the entire process that is wastewater treatment are nothing more than a stream or river in a box. No one is arguing that there are no differences between the stream or river and the treatment plant; for example, the treatment plant completes its treatment process 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 subject to the natural processes and to treat the solids that are generated through the treatment unit process steps. The typical wastewater treatment plant is designed to serve 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 would damage plant equipment or occupy treatment capacity without being treated.

• Primary treatment removes settleable and floatable solids (may not be present in all treatment plants).

• Secondary treatment removes BODs and dissolved and colloidal suspended organic matter by biological action; organics are converted to stable solids, carbon dioxide, and more organisms.

• Advanced waste treatment uses physical, chemical, and biological processes to remove additional BOD5, solids, and nutrients (not present in all treatment plants).

• 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 reduces the volume of the sludge by removing water.

The various treatment processes described above are discussed in detail later in this 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 wastewater they treat.

7.2 WASTEWATER SOURCES

The principal sources of domestic wastewater in a community are residential areas and commercials districts. Other important sources include institutional and recreational facilities and stormwater (runoff) and groundwater (infiltration). Each source produces wastewater with specific characteristics. Wastewater is generated by five major sources: human and animal wastes, household wastes, industrial wastes, storm-water runoff, and groundwater infiltration:

• Human and animal wastes include the solid and liquid discharges of humans and animals and are considered by many to be the most dangerous from a human health viewpoint. The primary health issue relates to the millions of bacteria, viruses, and other microorganisms (some of which may be pathogenic) present in the wastestream.

• Household wastes are wastes, other than human and animal wastes, that are discharged from the home. Household wastes usually contain paper; household cleaners; detergents; trash; garbage; pharmaceuticals and personal care products (PPCPs), which are products used by individuals for personal health or cosmetic reasons or by agribusiness to enhance the growth or health of livestock; and other substances the homeowner discharges into the sewer system.

• Industrial wastes include industry-specific materials that can be discharged from industrial processes into the collection system. They typically contain chemicals, dyes, acids, alkalis, grit, detergents, and highly toxic materials.

• Stormwater runoff is carried by collection systems designed to carry both the wastes of the community and stormwater. In this type of system, when a storm event occurs, the wastestream can contain large amounts of sand, gravel, and other grit as well as excessive amounts of water.

• Groundwater infiltration occurs when groundwater enters older, improperly sealed collection systems through cracks or unsealed pipe joints. This can add not only large amounts of water to waste-water flows but also additional grit.

Wastewater can be classified according to the sources of flows: domestic, sanitary, industrial, combined, or stormwater:

• Domestic (sewage) wastewater mainly contains human and animal wastes, household wastes, small amounts of groundwater infiltration, and small amounts of industrial wastes.

• Sanitary wastewater consists of domestic wastes and significant amounts of industrial wastes. In many cases, the industrial wastes can be treated without special precautions; however, in some cases, the industrial wastes will require special precautions or a pretreat-ment program to ensure that the wastes do not cause compliance problems for the wastewater treatment plant.

• Industrial wastewater includes industrial wastes only. Often the industry will determine that it is easier and more economical to treat its waste independent of domestic waste.

• Combined wastewater is the combination of sanitary wastewater and stormwater runoff. All of the wastewater and stormwater of a community is transported through one system to the treatment plant.

• Stormwater is carried by a separate collection system (no sanitary waste); it can include street debris, road salt, and grit.

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