A principal purpose of this chapter is to review the history of the treatment wetland technology. This effort will search for the kinds of thinking that went on during the development of the technology and, thus, it will provide perspective on the nature of ecological engineering. This is important since ecological engineering is a new field with a unique approach that combines ecology and engineering. Hopefully, a careful examination of the history of this example will reveal aspects of the whole field. The chapter will not attempt to describe the state-of-the-art in wetland waste-water treatment, especially since this has been done so well by Kadlec and Knight (1996) and others. Rather, the emphasis will be on the early studies. Examination of these studies, which were conducted in the 1970s and which are the "ancestors"
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Outlet sewer . ■' Gravel leaching beds.°."o°'-
sewer ¿.p kn%°o pc^fX^ 0 q & ° „ q » " ° „ o 0 0 c u f.f O oW J>. o.« cC IP » £ C o-'cit. c 1 Vo oTci" T *o o' c V -"T S't o ■ c^ o t *
FIGURE 2.1 View of a septic tank and leaching bed. (From Clapham, W. B., Jr. 1981. Human Ecosystems. MacMillan, New York. With permission.)
of the present technology, should yield insight into the thought processes of ecological engineering.
A summary of the old field of sanitary engineering from which conventional sewage treatment technologies have evolved is described first. This is followed by a discussion of the history of use of wetlands for sewage treatment, including the proposal of hypotheses about where the original ideas came from and who had them. It is suggested that ecologists played the critical role in the development of treatment wetland technology and that engineering followed the ecology. The conceptual basis of treatment wetlands is covered and the role of biodiversity is discussed with emphasis on several important taxa. A comparison is made of mathematical equations used to describe analogous decay processes in ecology and sanitary engineering, which indicates similarities between the fields. Finally, two variations of treatment ecosystems are examined in detail to demonstrate the design process: Walter Adey's algal turf scrubbers and John Todd's living machines.
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