Nitrogen compounds are becoming increasingly important in waste water management, because of the many effects that nitrogenous material can have on the environment. Nitrogen, in its various forms can deplete oxygen due to nitrification, fertilize aquatic plant growth, exhibit toxicity toward aquatic life, affect chlorine disinfection efficiency and present a public health hazard. These effects will be reviewed further in Section 1.4.
This volume is about the nitrogen removal processes applied in environmental technology. A detailed description of all processes, biological as well as physical-chemical, will be presented, but obviously the selection of environmental technology must be based not only upon what the technology can offer, but also upon which problems we need to solve. Before we can make the final selection of the proper technology, we need to answer a chain of questions:
1. What are the concentration and form(s) of the pollutants in the ecosystem in focus?
2. Are these concentrations and forms changed over time? If "yes" due to what processes? Can these processes be controlled?
3. What are the sources of the pollutants? Which sources are point sources and which sources are non-point or diffuse sources?
4. What is the geographical distribution of the problem(s)? Are the problems local, regional or global? The answers to this question require in most cases that a local, regional or global cycle of the pollutant is set up.
Figure 1.1. gives a flow chart of a procedure showing how to get from emission of mass and energy to a solution of the related environmental problems. Emission is translated into ¡mission and concentration. The effect and impact of a concentration of a compound or energy is found by considering all the chemical, physical and biological processes that take place in the ecosystem. This step will often require the application of ecological models as a management tool, as the processes are interactive and an overview is difficult to obtain without a synthesizing instrument as modelling; see Jorgensen (1988). This evaluation leads us hopefully to an acceptable ecological solution by the use of ecological engineering or environmental technology. The former attacks the problem in the ecosystem, which is often needed, when the cause of the problem is coming from non-point sources; the latter attempts to reduce or dilute the emission at the point source. This volume focuses on the environmental technological solutions to nitrogen removal, although the application of biological removal processes in nature, i.e., in the ecosystems, also will be touched upon, as these processes are in principle the same processes, such as the biological processes characterizing the biological nitrogen removal processes in environmental technology.
The three steps in the procedure presented in Fig. 1.1 concerned with ecosystems are the most complex ones. They require a very comprehensive ecological and environmental scientific knowledge, which often must be synthesized in a model in order to give applicable answers to the crucial environmental problems. It would require a second volume of this book to discuss in detail the nitrogen in the environment, but a brief discussion of these problems seems necessary to present the frames of the environmental technology available for nitrogen removal - or to touch upon the problems behind the possible solutions presented in parts B (removal of nitrogen by biological methods) and C (removal of nitrogen by physical-chemical methods) of the volume. Section A is a necessary part of this volume to avoid the separation of "the problem" and "the solution," which should always be avoided in environmental management. An integration of the two sides of environmental issues should always be attempted, and it is facilitated in the case of nitrogen pollutions by the fact, that many of the biological, chemical and physical processes used for nitrogen removal in environmental technology are, as mentioned above, the same as the processes that take place in nature. The following sections of this introductory chapter will consequently focus on:
- the global nitrogen cycles, to understand the global effects of our nitrogen emissions,
- the regional and local nitrogen cycles and budgets,
- the sources of nitrogen emission and their relative quantitative importance
- the typical effects of elevated nitrogen concentrations in aquatic ecosys-
terns and in portable water. This includes a brief presentation of the toxicity of nitrogen compounds.
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