1. DISSOLVED OXYGEN IN WATER

2. IMPORTANCE OF DISSOLVED OXYGEN
Aquatic animals need a minimum concentration of dissolved oxygen in water to survive
Dissolved-oxygen (DO) content indicates water quality
At 20°C oxygen content in water is about 9 ppm (parts per million)
Oxygen is non-polar so it has low solubility
Solubility of gas decreases with higher temps

3. WATER QUALITY Water Quality DO Level Good Quality (20°C, sea level
8-9 ppm O2
Moderate Pollution
4.5 ppm O2
Highly Polluted
<4.5 ppm O2
Factors affecting water quality:
Presence of disease causing pathogens/ microorganisms
Oxygen demanding wastes: organic substances (plants, animal/ human/ industrial waste)

4. BIOCHEMICAL OXYGEN DEMAND
Ppm BOD
Quality of Water
<1
Almost Pure 5
Doubtful Purity 20
Unacceptable Purity

5. BIOCHEMICAL OXYGEN DEMAND
Biochemical (Biological) Oxygen Demand (BOD): measure of oxygen consumed by biodegradable organic wastes and ammonia in a given time period/ amount of water (normally 5 days, 20° C)
Ppm BOD
Quality of Water
<1
Almost Pure 5
Doubtful Purity 20
Unacceptable Purity

6. AEROBIC DECOMPOSITION
Aerobic Decomposition: the breakdown and digestion of organic mater in water in the presence of oxygen and a bacteria-rich environment
Oxidation process
Removes oxygen from water so dissolved oxygen (DO) decreases and can kill aquatic life dependent on oxygen

7. AEROBIC CONVERSIONS Complex organic material
simple organic material + CO2 + H2O
nitrogen nitrates (NO3-)
sulfur sulfates (SO42-)
phosphorus phosphates (PO43-)

8. ANAEROBIC DECOMPOSTITION
Anaerobic decomposition: microorganisms not dependent on oxygen help decompose organic matter without oxygen present

9. ANAEROBIC CONVERSIONS
Typical Products in Presence of Water:
Nitrogen and Hydrogen
ammonia and amines (strong fishy smell)
Carbon and Hydrogen
methane (biogas/ marsh gas)
Organic Sulfur
hydrogen sulfide, H2S (rotten egg smell)
Phosphorus
phosphine, PH3

10. EUTROPHICATION
Eutrophication: the process by which water becomes lifeless
Plant nutrients (nitrates- waste and fertilizers, phosphates- detergents and fertilizers) lead to excessive growth of plant life (algal blooms)
Dead plants fall to the bottom of water
Decay in the presence of bacteria (depletes oxygen concentration)
Fish die due to lack of oxygen
Toxic substances are released into the water by anaerobic processes
Water becomes lifeless

11. THERMAL POLLUTION Thermal Pollution:
Origins: water used to cool/ condense steam in industrial processes is dumped into bodies of water which then become warmer
Effects: reduced levels of oxygen (gas concentration decreases as temperature increases)
Metabolic rates of aquatic animals increase and require more oxygen to survive