The perceptual structure of the physical and chemical characteristics of wastewater can change substantially with changes in stream habitats and their individual patterns. Wastewater physical characteristics include

1. Color: The physical appearance, qualitative significant color of wastewater depends on holding times in tanks, and varies from a light brown to light gray color. The color is known to turn dark gray or black in the event of wastewater going stale. A color change of wastewater is due to fermenta­tion of the various chemical compounds produced, in particular hydrogen sulfide and ferrous sulfide. Color can be measured by comparisons using standard methods.

2. Odor: The offensive odor in wastewater is mainly due to dissolved impuri­ties and a number of odor compounds produced by living enriched microbes and decaying aquatic organisms when under anaerobic conditions. The principal odor-producing compound is hydrogen sulfide, produced as gas by bacterial decomposition under anaerobic conditions.

3. Solids contents: The total solids are made up of both dissolved and sus­pended material that remains as residue in wastewater (Metcalf and Eddy, 1987) upon evaporation at 103°C to 105°C.

4. Temperature: The wastewater temperature will vary season to season and with the geographical location, from 10°C to 21°C (Muttamara, 1996). Temperature plays a major role in wastewater treatment, and its variation may cause changes as a result of the chemical and biological reactions of planktonic organisms. Wastewater contains bacteria and fungi that may have a substantial influence on the physical characteristics of the wastewa­ter, especially when in abundance due to abnormal temperatures. Turbidity and color are indirectly related to temperature because most of the chemical reaction products, including equilibrium of wastewater coagulation, can change with temperature. Temperature is also very important in the deter­mination of various parameters, such as changes in pH often occurring in regions with low acid neutralizing capacity, conductivity, different satura­tion levels of gases, various forms of alkalinity, etc.