Info

■v.. ✓ y •• --. • *

Distance Downstream ->■

Distance Downstream ->■

FIGURE 2.3 The longitudinal succession of various ecological parameters caused by the discharge of sewage into a river. A and B: physical and chemical changes; C: changes in microorganisms; D: changes in larger animals. (From Hynes, H. B. N. 1960. The Biology of Polluted Waters. Liverpool University Press, Liverpool, U.K. With permission.)

The term "filter" is a misnomer, because the removal of organic material is not accomplished with a filtering or straining operation. Removal is the result of an adsorption process which occurs at the surfaces of biological slimes covering the filter media. Subsequent to their absorption, the organics are utilized by the slimes for growth and energy.

The gravel or other materials provide a surface for microbes that consume the organic material in sewage. The bed of gravel also provides an open structure that allows a

Streeter Phelps Model
FIGURE 2.4 Several views of the Streeter-Phelps model of biodégradation of sewage in a river ecosystem. (From Odum, H. T. 1983. Systems Ecology: An Introduction. John Wiley & Sons, New York. With permission.)

free circulation of air for the aerobic metabolism of microbes, which is more efficient than anaerobic metabolism. A relatively high diversity of organisms colonizes the tank because it is open to the air. Insects, especially filter flies (Pschodidae), are important as grazers on the "biological slimes" (Sarai, 1975; Usinger and Kellen, 1955). For optimal aerobic metabolism the film of microbial growth should not exceed 2 or 3 mm, and the invertebrate animals in the trickling filter help to maintain this thickness through their feeding. The overall diversity of trickling filters is depicted with traditional alternative views of ecological energy flow in Figure 2.6 and Figure 2.7. The food web (Figure 2.6) describes the network of direct, trophic (i.e., feeding) interactions within the ecosystem. Both the topology of the food web networks (Cohen, 1978; Cohen et al., 1990; Pimm, 1982) and the flows within the networks (Higashi and Burns, 1991; Wulff et al., 1989) are important subjects in ecological theory. The trophic pyramid (Figure 2.7) describes the pattern of amounts of biomass or energy storage at different aggregated levels (i.e., trophic levels) within the ecosystem. Methods for aggregation of components, such as with trophic levels, are necessary in ecology in order to simplify the complexity of ecosystems. For example, a trophic level consists of all of the organisms in an ecosystem that feed at the same level of energy transformation (i.e., primary producers, herbivores,

FIGURE 2.5 View of a typical trickling filter system. The distributor arms, a, are supported by diagronal rods, b, which are fastened to the vertical column. c. This column rotates on the base, d, that is connected to the inflow pipe. e. The sewage flows through the distributor arms and from there to the trickling filter by means of a series of flat spray nozzles, f, from which the liquid is discharged in thin sheets. The nozzles are staggered on adjacent distributor arms in order for the sprays to cover overlapping areas as the mechanism rotates. The bottom of the filter is underdrained by means of special blocks or half-tiles, g, which are laid on the concrete floor, h. (From Hardenbergh, W. A. 1942. Sewerage and Sewage Treatment (2nd ed.). International Textbook Co., Scranton, PA.)

FIGURE 2.5 View of a typical trickling filter system. The distributor arms, a, are supported by diagronal rods, b, which are fastened to the vertical column. c. This column rotates on the base, d, that is connected to the inflow pipe. e. The sewage flows through the distributor arms and from there to the trickling filter by means of a series of flat spray nozzles, f, from which the liquid is discharged in thin sheets. The nozzles are staggered on adjacent distributor arms in order for the sprays to cover overlapping areas as the mechanism rotates. The bottom of the filter is underdrained by means of special blocks or half-tiles, g, which are laid on the concrete floor, h. (From Hardenbergh, W. A. 1942. Sewerage and Sewage Treatment (2nd ed.). International Textbook Co., Scranton, PA.)

primary carnivores, etc.). Magnitudes are shown visually on the trophic pyramid by the relative sizes of the different levels. A pyramid shape results because of the progressive energy loss at each level due to the second law of thermodynamics. Energy flow is an important topic in ecology though the concept of "flow" is an abstraction of the complex process that actually takes place. Colinvaux (1993) labels the abstraction of the complex process that actually takes place. Colinvaux (1993) labels the concept as a hydraulic analogy in reference to the simpler dynamics of water movements implied by the term, flow. McCullough (1979) articulated the abstraction more fully as follows,

The problem concerns energy flux through the system; because it is unidirectional, and perhaps because of a poor choice of terminology, an erroneous impression has developed. Ecologists speak so glibly about energy flow that it is necessary to emphasize that energy does not "flow" in natural ecosystems. It is located, captured or cropped, masticated, and digested by organisms at the expense of considerable performance of work. Far from flowing, it is moved forcibly (and sometimes even screamingly) from one trophic level to the next.

Studies of energy flow, while imperfect in method, provide empirical measurements of ecological systems for making synthetic comparisons and for quantifying magnitudes of contributions of component parts to the whole ecosystem.

essential components

(sewage)

(light)

(effluent (detritus nonliving components nonessential components essential components

(sewage)

(light)

nonessential components

substrate producers

- consumers terminal

(effluent (detritus substrate producers

- consumers

Was this article helpful?

0 0
Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

Get My Free Ebook


Post a comment