1. Study Guide Questions: 30 - 32

2. Turbidity (cloudiness of water)
Turbidity is caused by particulates suspended in water
Particulates can be either organic or inorganic
Turbidity can occlude sunlight in water bodies harming photosynthetic plants
Particulates can act as habitat for microorganisms; removal of particulate removes organisms.
Flocculation is a common way to remove particulates. It brings together large numbers of small
particles to make larger particles which will settle out of water.
When the particles settle out, they take the organisms (potentially pathogenic) with them.

3. BOD: Biological Oxygen Demand
organic
Additionally, organic particulates can be a carbon source for organisms
Aerobic Heterotrophic organisms consume carbon compounds and
as part of their metabolism and growth, they also consume O2

4. So, if water containing high amounts of organic materials is added to a
water body, for example, treated wastewater, aerobic heterotrophs will
consume those organic materials and in the process use up oxygen
reducing the amount of oxygen available to other life in the lake or stream.
The ability of water (e.g. wastewater) to promote this activity is indicated
By its biological oxygen demand (BOD). If there is a large quantity of organic
waste in the water supply, there will also be a lot of bacteria present
working to decompose this waste. In essence it creates a demand
on oxygen due to the activity of aerobic heterotrophic organisms.
The higher the BOD the greater the potential to lower oxygen contents
of surface water bodies including rivers and lakes.
Pristine rivers: < 1 mg/L
Moderately polluted rivers: 2 – 8 mg/L
Treated wastewater 20 mg/L