DISSOLVED OXYGEN

OXYGEN

A Soluble gas.A colorless, odorless, tasteless,

gaseous chemical element that occurs free in the atmosphere. It is very active, combines with nearly all other elements, is the most common element in the earth's crust, and is essential to life processes and to combustion.

OXYGEN: AQUATIC LIFE DEPENDS ON IT

Both aquatic plants and animals depend on dissolved oxygen for survival. Lack of dissolved oxygen can cause aquatic animals to quickly leave the area or face death. Under low oxygen conditions, the aquatic animal community changes quickly. Under extreme conditions, lack of oxygen can kill aquatic plants and animals.

CO2 O2

What Is Dissolve Oxygen In Water?

Dissolve Oxygen (DO) - Oxygen gas that is dissolved into water. DO is essential for rivers, streams, lakes, and aquatic life. It is a positive sign to have DO in water. If there is an absence of oxygen in water, it can be a sign of severe pollution. Water ranges from very high levels of DO to very low levels of DO. Sometimes the DO is so low, there is hardly any aquatic life.

DO Level (in ppm)

0.0 - 0.04

4.1 - 7.9

8.0 - 12.0

Water Quality

Poor

Fair

Good

Factors Affecting DO Volume and velocity of water flowing in the

water body. Climate/Season Salinity The type and number of organisms in the

water body. Dissolved or suspended solids Amount of nutrients in the water Organic Wastes Altitude Groundwater Inflow

EFFECTS OF TEMPERATURE IN DO

Maximum dissolved oxygen concentrates

vary with temperatureTemperature

(°C)DO

(mg/l)Temperature

(°C)DO

(mg/l)Table 5.3

Maximum dissolved

oxygen concentrat

es vary with

temperature

0 14.60 23 8.561 14.19 24 8.402 13.81 25 8.243 13.44 26 8.094 13.09 27 7.955 12.75 28 7.816 12.43 29 7.677 12.12 30 7.548 11.83 31 7.419 11.55 32 7.2810 11.27 33 7.1611 11.01 34 7.1612 10.76 35 6.9313 10.52 36 6.8214 10.29 37 6.7115 10.07 38 6.6116 9.85 39 6.5117 9.65 40 6.4118 9.45 41 6.4119 9.26 42 6.2220 9.07 43 6.1321 8.90 44 6.0422 8.72 45 5.95

How Is Dissolved Oxygen Measured?

DO concentration can be reported as milligrams per litre, parts per millions, or as percent air saturation. 1 milligram per litre is equal to 1 part per million. 100% air saturation refers to the amount of dissolved oxygen that would be in water if it were completely saturated with air.

METHODS OF MEASURING DO:

1. DISSOLVED OXYGEN METER

- A DO meter measures the pressure of oxygen in water.

2. MODIFIED WINKLER DISSOLVED OXYGEN DETERMINATION

- In the modified Winkler method, various chemicals are added to the water sample.  Then Sodium Thiosulfate is titrated into the sample. The dissolved oxygen concentration can be calculated based on the amount of titrant added to the sample. The formula used is:

Dissolved Oxygen Technology

Three common electrochemical sensors technology:

Galvanic Dissolved Oxygen SensorPolarographic Oxygen SensorOptical Dissolved Oxygen Sensor

Galvanic Dissolved Oxygen Sensor

Polarographic Oxygen Sensor

Optical Dissolved Oxygen Sensor