Study Guide Questions: 30 - 32

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.

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

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