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Organic 40 mg/l

Mineral 10 mg/l

Dissolved 450 mg/l

Organic 160 mg/l

Mineral 290 mg/l

FIG. 7.1.4 Classification of solids found in medium-strength wastewater. (Metcalf and Eddy, Inc., 1991.)

Odors in wastewater are caused by gases from decomposition or by odorous substances within the wastewater. Table 7.1.10 lists examples of odorous compounds associated with untreated wastewater.

Organic matter in wastewater can be related to oxygen demand and organic carbon measurements. Table 7.1.11 shows several measures of organic matter. BOD refers to the amount of oxygen used by a mixed population of mi-

croorganisms under aerobic conditions that stabilize organic matter in the wastewater. The 5-day BOD is primarily composed of carbonaceous oxygen demand, while the 20-day BOD includes both carbonaceous and nitrogenous oxygen demands. Figure 7.1.5 is a typical BOD curve, developed via laboratory measurements, for domestic wastewater. The following relationships and definitions are associated with Figure 7.1.5 (Qasim 1985):

UOD = Lo + L y = L0(1 - e-Kt) LoT = Lo(0.02T + 0.60) Kt = K(1.047)T-20

where:

UOD = ultimate oxygen demand, mg/l

nitrogenous oxygen demand or second stage BOD, mg/l ultimate carbonaceous BOD, or first stage BOD at 20°C, mg/l (for domestic wastewater BOD5 is approximately equal to £H Lo) carbonaceous BOD at any time t, mg/l ultimate carbonaceous BOD at any temperature T°C, mg/l reaction rate constants at 20°C, d-1 (for domestic wastewater K = 0.2 to 0.3 per d) reaction rate constant to any temperature T°C, d-1

For medium-strength domestic wastewater, about 75% of SS and 40% of FS are classified as organic. The main groups of organic substances in wastewater include proteins (40-60%), carbohydrates (25-50%), and fats and oils (10%) (Metcalf and Eddy, Inc. 1991). Urea, a constituent of urine, is also found in wastewater along with numerous synthetic organic compounds. Synthetic compounds include surfactants, organic priority pollutants, VOCs, and agricultural pesticides.

The U.S. Environmental Protection Agency (EPA) has identified 129 priority pollutants in wastewater; these pol-

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