Environmental Engineering: Fundamentals and Design - Chapter 11

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# Chapter 11 Wastewater Treatment

James R. Mihelcic, David W. Hand and Martin T. Auer

## Introduction

Here, we will consider the reasons why such treatment is needed, the nature of the materials which are removed from wastewaters and explore the processes that accomplish that removal. We will consider wastewater treatment in cities, in small communities, at individual homes and even aboard the international space station. | Portage Lake Wastewater Treatment Plant Houghton - Hancock, Michigan
Domestic and industrial wastes are treated before being discharged to rivers and lakes to guarantee safe recreation and to protect the wildlife that call those environments home. While modern technology offers remarkable capabilities to accomplish these goals, the introduction of new and different pollutants and the cost of treating to required levels is a challenge for the wastewater treatment industry.

### Regulations

Our nation's laws related to water quality were amended in 1972 and then again in 1977, with passage of the Clean Water Act (CWA). The primary goal of this legislation was to make sure that our waters were "fishable - swimmable" (Provision 2 below). Water quality standards are set by the U.S. Environmental Protection Agency to protect uses for surface waters such as fishing and swimming. If the standards are not met, then a calculation is made to determine how much of a pollutant can be discharged to the lake or river without exceeding the standards. This amount is called the Total Maximum Daily Load (TMDL). Under the National Pollutant Discharge Elimination System (NPDES), all discharges of wastewater to surface waters must have a permit. The allowable pollutant loads set in the permits can be adjusted to meet the TMDL objective and make sure that water quality goals are met.
| The Portage Lake Wastewater Treatment Plant laboratory. Regular tests are run to make certain that the treated wastewater meets permit requirements.

### Treatment Overview

Pretty much everything that happens in a wastewater treatment plant would happen in nature anyway. Pathogens would die. Solids would settle to the lake bottom. Nutrients would be removed from the water by plants. Organic matter would decompose. And, toxic materials would eventually move into the air or into the bottom sediments of a river or lake. In the process, however, the health of humans and wildlife would be threatened and our waters would no longer be fishable and swimmable.

The trick with wastewater treatment is that we hold the water within the plant until natural and engineered processes can remove the pollutants form the waste stream. We essentially do what nature does, but in a carefully controlled environment separated from natural ecosystems.

Water Environment Federation's
wastewater treatment overview, Go With The Flow.

The basic steps in wastewater treatment are:

- preliminary treatment - to protect plant operation;

- settling - to remove solids;

- biological treatment - to remove organic matter;

- disinfection - to remove pathogens; and

- solids processing - to provide safe final disposal.

#### Credits

River Pollution animation: © 2007 State of Michigan.
Portage Lake Wastewater Treatment Plant photo: Courtesy of Portage Lake Water and Sewer Authority (Houghton, MI).
Clean Water Act text: Environmental Protection Agency.
Wastewater Treatment Plant Lab photo: Andy Whaley (Michigan Tech).

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