Dissolved Oxygen in Water

With real-life, horrifying sea creatures on every slide.

Dissolved OxygenThe concentration of oxygen in the water.Known as DOLowest amount needed for fish is 0.003g/dm3

Dissolved OxygenThe highest DO possible is 0.009g/dm3

Oxygen has low solubility because the diatomic molecule is non-polar.

Rivers have higher DO because of the rushing water, and can replace its DO faster.

BOD (IB Assessment)Biochemical Oxygen DemandIt’s the amount of oxygen (in ppm) needed by

bacteria to decompose organic waste in water at a specified time at a specified temperature (usually 5 days at 20⁰C).

A measure of pollution

BOD (IB Assessment)The higher the BOD, the more polluted the water

is, the more oxygen needed to oxidize the water. The more oxygen present in the water, the lower

the BOD should be. Fish (and other organisms) cannot survive in an

environment where the BOD is greater than the DO.

BOD TableBOD Quality of water

<1 Almost pure

5 Doubtful purity

10 Unacceptable purity

100-400 Sewage water

100-10,000 Water from meat-processing plant

Winkler MethodMethod to figure out the BOD.The water is saturated to its maximum amount of

DO.Bacteria is left in the water for five days in a

temperature of 25⁰C.The remaining oxygen is measured using

titration.

Aerobic vs. Anaerobic (IB Assessment)Aerobic Decomposition

Anaerobic Decomposition

Uses oxygen Oxidizes compounds

Does not use oxygenReduces compoundsCreates a bad smell

Decay ProductsElement Aerobic Decay

ProductsAnaerobic Decay Products

Carbon CO2 CH4

Hydrogen H2O CH4, NH3, H2S, H2O

Oxygen H2O H2O

Nitrogen NO3- NH3 and amines

Sulfur SO42- H2S

Phosphorus PO43- PH3

Eutrophication (IB Assessment) Addition of nutrients to the point of excess

(usually from fertilizers or acid rain).Overabundance of plants and algae. Due to overabundance, all the oxygen in the

water is used up, and the plants die. Creates a lot of organic matter to be

decomposed, raising the BOD.

Eutrophication (IB Assessment)Because of the lack of oxygen, anaerobic decomposition

takes place, creating bad smelling gases that poison the water.

Area dies completely from the lack of oxygen and poisonous compounds.

Calcium or aluminum ions can be used to remove the phosphates.

Nitrates are much harder to remove, reverse osmosis and ion exchange techniques are needed.

Thermal Pollution (IB Assessment)Water used for cooling in powerplants are

dumped into rivers, causing thermal pollution.Thermal pollution decreases the concentration of

oxygen.Thermal pollution increases metabolism,

increasing the amount of oxygen needed for respiration, and therefore increasing the BOD.

Thermal Pollution (IB Assessment)With a decrease in oxygen concentration and an increase in

the BOD, the environment cannot be supported, and anaerobic respiration takes place.

Sudden increase in temperature can disrupt life cycles such as reproduction, or just kill organisms (increasing the BOD).

Can be solved by trickling water through a porous material while blowing air in the opposite direction

The End