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 Aquatic Health: ~< 5 mg/L DO poor for aquatic fish ~10 mg/L ideal DO concentrations

Langelier Saturation Index (LSI) Factoids Aggressive (corrosive) or scaling condition of water Online calculator Precipitate or Dissolve CaCO 3 Difference between pH of water and pH of CaCO 3 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= + CaCO 3 will precipitate (scaling) +1 mild scale, +4 severe scale LSI = - CaCO 3 will dissolve (corrosion) -1 mild, -5 severe Factoids Aggressive (corrosive) or scaling condition of water Online calculator Precipitate or Dissolve CaCO 3 Difference between pH of water and pH of CaCO 3 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= + CaCO 3 will precipitate (scaling) +1 mild scale, +4 severe scale LSI = - CaCO 3 will dissolve (corrosion) -1 mild, -5 severe

Langelier Saturation Index (LSI) Saturation IndexDescriptionGeneral Recommendation - 5Severe CorrosionTreatment Recommended - 4Severe CorrosionTreatment Recommended - 3 Moderate Corrosion Treatment Recommended - 2Moderate CorrosionTreatment May Be Needed Mild CorrosionTreatment May Be Needed -0.5None- Mild Corrosion Probably No Treatment 0Near BalancedNo Treatment 0.5Some Faint Coating Probably No Treatment 1Mild Scale CoatingTreatment May Be Needed 2Mild to Moderate CoatingsTreatment May Be Needed 3 Moderate Scale Forming Treatment Advisable 4Severe Scale FormingTreatment 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 = 120 o F, 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 120 o = 1.7 pH(s) Sum= 7.32 pH actual = 8.0 – 7.32= +.68 pH (s) = pCa= 2.92 pAlk=2.7 “C” at 120 o = 1.7 pH(s) Sum= 7.32

Langelier Saturation Index (LSI) Hardness=120 mg/L 2.92 PCa 2.70 P(Alk) 1.7 C at 120 o P Alk=100 mg/L TDS=210 mg/L