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EPA/625/R-93/010

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Process Design Manual: Nitrogen Control



Abstract:

This manual is an update and revision of the original 1975 edition. It strives to maintain the high technical quality and generous provision of reference materials provided by the 1975 edition, although it represents a significant shift in overall content. Given the experience of the past 18 years, the focus of this second edition is directed to those biological/mechanical systems that have found widespread use for nitrification and nitrogen removal. Design criteria for physical/chemical systems are not provided; however, there is a brief discussion of such processes in Chapter 2, in which their applicability under specific site conditions and wastewater applications is addressed. The design of natural systems also is not considered within the context of this manual, except in the planning and development of alternatives for technology selection, a point of discussion within Chapter 2. Adequate references are given in Chapter 2 to assist the reader in seeking design information on both natural systems and physical/chemical processes.

The primary audience is the designer of small to medium sized facilities, although the application of the manual is not limited to any range of plant sizes. Detailed theoretical discussions are not provided. Rather, the manual focuses on the major process and design aspects considered in the development of an effective design. It begins with process basics and proceeds to the presentation of detailed design criteria and the development of process designs, using examples to demonstrate calculation sequences. In addition, the manual is organized to help the designer in the planning stages of a facility, highlighting important process and O and M considerations.

The manual also is assembled for use as a desk reference or handbook. In addition to aiding designers, the manual can serve as a source for reviewers, operator, regulators, and manufacturers.

The manual progresses from a broad discussion of nitrogen in the environment, to the concepts of using biological processes to control or remove nitrogen, and finally to the details of designing specific systems. The first chapter describes the relationships of nitrogen in the environment. The fundamental purpose of the manual, implementation of nitrogen controls in municipal systems, is brought into focus in Chapter 2 by outlining design principles. Issues are presented that enter into the designer's strategy. The chapter discusses the relative importance of each issue in order to help the designer avoid pitfalls before they are compounded by the growing detail of design. Chapters 3 and 4 give the theoretical foundations of the nitrification and denitrification processes by drawing on concepts of microbiology, chemistry, and kinetics. Although the discussions of mathematical and computer modeling in Chapter 5 are intended to stand independently from the other chapters, they provide a useful bridge between Chapters 3 and 4 and Chapters 6, 7, and 8.

In the latter three chapters, the conceptual bases of nitrification and denitrification are developed to design criteria, and design examples are presented to assist in producing a specific configuration that will meet performance objectives. Chapter 6 addresses suspended growth and attached growth configurations for biological nitrification. Denitrification processes are addressed in Chapter 7, but only as applied in a separate stage using a supplemental carbon source. The current trend has been to accomplish nitrification and denitrification in single-sludge systems, using wastewater carbon for the denitrification step.

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