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Introduction

1.1 Role of Hydraulics and Pneumatics in Environmental Engineering Design

The environmental engineer has historically been the leading professional in water supply and wastewater collection and disposal. In that capacity, he or she was earlier known as a sanitary engineer, a reflection of the public health significance of those endeavors. As this spectrum of activities broadened to deal with the environmental problems facing an increasingly complex society and as the broader environmental objectives of the sanitary engineer's endeavors became apparent, the term environmental engineer became more popular within the profession. The aforementioned objectives include protection of drinking water supplies, protection and propagation of aquatic life, aesthetic and recreational aspects, and agricultural (livestock water supply and irrigation) and industrial water supply. In 1972, the Sanitary Engineering Division of the American Society of Civil Engineers formally changed its name to the Environmental Engineering Division. The environmental engineer's areas of activity were at that time considered to include the following: air pollution, environmental quality, water supply, municipal wastes, industrial wastes, agricultural wastes, urban (and rural) land runoff, thermal pollution, nuclear energy, and solid wastes. It was noted that all civil engineers (and other engineers as well) deal with the environment. However, the sole focus of the environmental engineer is on environmental protection as opposed to production or environmental modification. Whereas other branches of engineering deal with activities of potential impact on the environment, that is not their primary interest. Environmental engineering has a singular concern and responsibility for environmental protection.

Hydraulics is the engineering art and science dealing with the macroscopic, physical behavior of liquids. Relating this definition to the above areas of activity, environmental engineering hydraulics deals with the hydraulic aspects of: the environmental quality of water in the hydrologic cycle: municipal and industrial water supply; municipal, industrial, and agricultural wastewaters and stormwater runoff plus thermal and nuclear pollution and solids wastes. Environmental quality is impacted by the above wastewater and stormwater runoff plus thermal and nuclear pollution and solid waste.

Pneumatics is the art and science of dealing with the movement of air, generally in human-made systems. (Its inclusion makes this book's title a slight misnomer.) In environmental engineering applications, pneumatic systems assumed initial importance in the aeration of activated sludge. Now air and other gases (mentioned in Chapter 9) play an important role in a wider range of the abovementioned areas of activity. The emphasis in this book is on pneumatic (air) systems, but many of the principles are more generally applicable.

In providing the services mentioned above, the environmental engineer integrates various natural sciences and engineering disciplines. This integration is the result of his or her own interdisciplinary training and experience, and the support of other professionals. The water-oriented environmental engineering curriculum usually provides a smattering of chemistry, microbiology, aquatic ecology, and process theory. The latter entails a mixture of fundamental science and empiricism relating to influent and effluent characteristics of unit processes. Practicing engineers apply this knowledge with the consulting support of specialists within their own field (most particularly process specialists and aquatic chemists). The supporting role of the aquatic ecologist is relatively recent and increasing. The support of the chemist and aquatic ecologist is most significant during the preliminary design phase when treatment processes are being selected and environmental impact assessed.

During the design phase of a project, the support of other design professionals is commonly provided. These include architects, structural engineers, electrical and instrumentation engineers, and mechanical engineers. The latter generally design, as a minimum, the HVAC (heating, ventilating, and air conditioning) and plumbing systems. In some large consulting firms, mechanical engineers may design process piping, pump systems, and the like, although the environmental engineer is called upon to do this in many offices. Through his training (both formal and on-the-job) and the professional assistance of equipment manufacturers, the environmental engineer is usually capable of handling many aspects of the "mechanical" design.

Although of major significance, the hydraulic engineering aspects present a particular challenge and somewhat of an anomaly in this scheme of things. The environmental engineer is not often trained beyond the undergraduate level in fluid mechanics; many graduate environmental engineering curricula do not include a hydraulic engineering course. Equipment manufacturers are only a limited source of professional support since hydraulic structures (including process tanks) are generally made of concrete with mechanical equipment constituting a small fraction of the cost. Environmental engineering textbooks and design manuals provide some practical hydraulics, but they are often oversimplified and erroneous. Hydraulic engineers are often appalled at the "hydraulics" presented in the environmental engineering literature. Ironically, most hydraulic and environmental engineers have civil engineering backgrounds, and yet the methods of these two branches of civil engineering have not been well integrated. Engineering firms, particularly larger ones, may have one or more engineers with graduate-level training in hydraulics whose advice and review are solicited. This serves both to improve the design and the hydraulic knowledge of the environmental engineers who are exposed to this input. However, hydraulic engineering expertise is often not available; environmental engineering systems do not commonly incorporate the major hydraulic structures that justify a hydraulic engineering staff such as might be found in a hydroelectric design firm.

Furthermore, even when available, the hydraulic engineer may have had little experience with the unique environmental systems.

The availability of hydraulic engineers with experience in environmental engineering systems would reasonably resolve the problems referred to above. However, there is an additional dimension to consider. All water-oriented environmental engineering processes, both in constructed facilities and in the environment, are largely hydraulic processes, and many are predominantly so. However, there is a large gap between hydraulic engineering and environmental engineering technology. The environmental engineer's understanding of the processes with which he is concerned would greatly benefit from an understanding of hydraulic fundamentals. This benefit would extend to research efforts as well as practical applications.

The author has become of the opinion that hydraulics should be as much a part of the environmental engineer's fundamental background as chemistry and microbiology. It is hoped that the chapters which follow speak for themselves in this regard and that the reader will eventually share this opinion.

1.2 Scope, Organization, and Approach

1.2.1 Scope and Organization

Following this introductory chapter are four chapters (Chapters 2 through 5), which deal with basic hydraulic concepts and provide the theoretical foundation for the subsequent chapters. They do, however, incorporate some practical information, which stands by itself. Chapter 2 rigorously employs system and control volume concepts in the presentation and application of mass, momentum, and energy relations. This has been a sound trend in engineering education, and the author believes it to be unifying and of practical importance in the broader range of applications that includes, e.g., open-channel flows. The importance of the Navier-Stokes equations and dissipation function (Chapter 3) lies partially in their relation to "G-value," a seriously misapplied notion that has gained undue prominence. This book attempts to correct the notion of G-value and provide (in later chapters) suitable alternatives. The Navier-Stokes equations are also used (Chapter 4) as a point of departure for the unified discussion of various types of flow. Dimensional analysis (Chapter 5) is dealt with as an important concept that deserves greater attention, both for the perspective it provides and as an analytic tool.

From Chapter 6 on, the book deals with specific applications of the basic concepts presented earlier. Chapters 6 through 14 deal essentially with man-made environmental engineering systems. Although Chapters 6 through 13 fall within the conventional provinces of hydraulics and pneumatics, they are considered here from the standpoint of the environmental engineer's applications. This seems very useful and is done here for the first time known to the author. Chapter 14 deals with process applications from what the author believes is a sound and useful hydraulic perspective. In the design and research aspects of treatment processes, the significance of hydraulics needs greater appreciation. There is a significant disparity between existing knowledge in the field of hydraulics and its applications to treatment processes. The...