Water Quality
Presented By: Group 2
River Water Quality
Dissolved Oxygen (mg O2 /L) – is
required to maintain a balanced
community of organisms in lakes, rivers,
and the ocean.
 Deoxygenation – the rate at which
oxygen is consumed in oxidizing an
oxygen-demanding waste.
 Reaeration – the rate at which the
oxygen is resupplied from the
atmosphere.

Oxygen Saturation and Deficit

Saturation concentration (DOsat) – the
amount of oxygen that can be dissolved in
water at a given temperature.
 Henry’s law constant (Kh) –
(1.36 x 10-3 moles/L-atm at 20°C)
 Partial pressure of oxygen in the temperature
(PO2 ) – 21 percent or 0.21 atm
Formula for DOsat:
DOsat = Kh x PO2
Formula for D:
D = DOsat – DOact
where: D = oxygen deficit
DOact = ambient DO conc. from
saturation
Example 8.2

Determine the saturation dissolvedoxygen concentration, Dosat at 20°C.
Solution:
Dosat = 1.36 x 10-3 mole/L-atm x 0.21 atm
= 2.85 x 10-4 mole / L
Convert to mg O2/L:
Dosat = 2.85 x 10-4 mole/L x 32 g O2/mole x 103 mg O2
mole O2 g O2
= 9.1 mg O2 /L
Example 8.3
Determine the dissolved-oxygen deficit, D,
at 20°C for a river with an ambient
dissolved-oxygen concentration of5 mg
O2/L.
Solution:

D = 9.1 – 5 = 4.1 mg O2/L
Wetlands
A site may be characterized as wetland if
it is:
(1) Is inundated and saturated with water
for at least part of the year.
(2) Has hydric soils
(3) Supports predominantly hydrophytic
plants

Wetlands

Serve several important functions:
- water storage and flood mitigation
- filtration of water and removal of 1
suspended solids, bacteria, nutrients
and toxic substances
- wildlife habitat
- biogeochemical cycling of materials
- removes substances that may impair
water quality