Dissolved Oxygen
WQT 134
Environmental Chemistry II
Dissolved Oxygen
Key Words
• Dissolved Oxygen- The amount of oxygen in
a sample. Impacted by flow rate,
photosynthesis, aerobic respiration,
elevation, clarity, temperature, sludge
deposits, and water depth
Dissolved Oxygen
Temp: Colder the water the more DO it can hold. As temp
goes down DO goes up.
Dissolved Oxygen
Temp: Warm turbid water will have low DO values. Wetlands
Dissolved Oxygen
Elevation: At higher elevations, less oxygen can be dissolved
in water.
Dissolved Oxygen
Photosynthesis: dissolved oxygen concentrations may be
very low in the morning, and very high in the afternoon
Dissolved Oxygen
Flow rate: Increased flow rate increased mixing of DO into the
water.
Dissolved Oxygen
Sewage: Increased sewage can lower DO in the water.
Dissolved Oxygen
Aquatic Health:
~< 5 mg/L DO poor for aquatic fish
~10 mg/L ideal DO concentrations
Langelier Saturation Index (LSI)
Factoids
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Aggressive (corrosive) or scaling condition of water
Online calculator
Precipitate or Dissolve CaCO3
Difference between pH of water and pH of CaCO3
LSI= pH (actual) – pH (s)
– pH (actual) =measured pH of water
– pH (s)= theoretical pH at which the water will be saturated with calcium
carbonate. Takes into account Ca ion [], alkalinity, pH, Temp, and TDS
LSI=0 water is stable (rare)
LSI= + CaCO3 will precipitate (scaling)
+1 mild scale, +4 severe scale
LSI = - CaCO3 will dissolve (corrosion)
-1 mild, -5 severe
Langelier Saturation Index (LSI)
Saturation Index
Description
General Recommendation
-5
Severe Corrosion
Treatment Recommended
-4
Severe Corrosion
Treatment Recommended
-3
Moderate
Corrosion
Treatment Recommended
-2
Moderate Corrosion
Treatment May Be Needed
-1
Mild Corrosion
Treatment May Be Needed
-0.5
None- Mild Corrosion
Probably No
Treatment
0
Near Balanced
No Treatment
0.5
Some Faint Coating
Probably No
Treatment
1
Mild Scale Coating
Treatment May Be Needed
2
Mild to Moderate Coatings
Treatment May Be Needed
3
Moderate Scale
Forming
Treatment Advisable
4
Severe Scale Forming
Treatment Advisable
Langelier Saturation Index (LSI)
Exercise Determine the Langelier index for a water sample with the following characteristics, using the
Powell, Bacon and Lill diagram: Temperature = 120oF, M-Alk = 100 mg/L, Ca-hardness = 120 mg/L, pH = 8,
total dissolved solids = 210 mg/L.
LSI= pH (actual) – pH (s)
pH actual = 8.0 – 7.32= +.68
pH (s) =
pCa= 2.92
pAlk=2.7
“C” at 120o= 1.7
pH(s) Sum= 7.32
Langelier Saturation Index (LSI)
1.7 C at 120o
2.92 PCa
2.70 P(Alk)
P Alk=100 mg/L
Hardness=120 mg/L
TDS=210 mg/L