1. Water pollution can be defined as "the presence of a substance in the environment
that because of its chemical composition or quantity prevents the functioning of
natural processes and produces undesirable environmental and (human) health
2.Biochemical/Chemical Categories of Water Pollutants
·Rapidly degradable (non-persistent)
·Slowly degradable (persistent)
3. Legal Categories of Water Pollutants
a. Non-pont-source pollutants
b. Point-source pollutants
4. Pollutant Classes (These are not mutually exclusive classes)
b. Organic wastes
c. Chemical pollutants
Fig. 18.1 Pollution is an outcome of otherwise worthy human endeavors. Major categories of pollution and their causes are shown.
Fig. 18.2 Point sources are far easier to identify and correct than the diffuse nonpoint sources.
Fig. 18.5 The ecosystem of a stream differs with different sediment bedloads. This figure shows (a) Low sediment bedload and (b) High bedload.
II. Eutrophication - What Happens when Organic Wastes, Sediments, and Nutrients are not Controlled/
A. What is an Oligotrophic Body of Water?
B. What is a Eutrophic Body of Water?
C. How do you create a Eutrophic Body of Water?
1. Nutrient enrichment
2. Increased phytoplankton growth resulting in increased turbidity
3. Loss of food, habitat and dissolved oxygen from the loss of benthic plants
4. Depletion of dissolved oxygen from decomposition of phytoplankton by
D. How to Stop Eutrophication
1. Attack the symptoms:
a. Chemical treatments
c. Harvest aquatic weeds
d. Draw water down
2. Attack the root cause:
a. Control point-source pollutants
b. Control non-point-source pollutants
Fig. 18.6 Benthic (bottom-rooted) plants are submerged or emergent. Phytoplankton are single-celled or colonial floating plants.
Fig. 18.7 As nutrients are added from pollution sources, an oligotrophic system rapidly becomes eutrophic and undesirable.
Fig. 18.9 When washings from animal facilities are flushed directly into natural waterways, they contribute significantly to eutrophication. This may be avoided by collecting the flushings in ponds from which both the water and the nutrients may be recycled.
III. More of Attacking the Root Cause: Sewage Treatment
A. Collection of Sewage
B. What is in Raw Sewage
1. Debris and grit
2. Particulate organic matter
3. Colloidal and dissolved organic matter
4. Dissolved inorganic matter
6. Heavy metals, pesticides, and various other toxic compounds
C. How Do We Remove These Substances from the Water?
1. Preliminary Treatment - debris and grit removed by a bar screen and grit
denitrification and bacterial uptake of phosphorus
a. Can also be done inorganically by using chemical processes
·Lime causes phosphate to precipitate as insoluble calcium phosphate
·Ferric chloride causes phosphate to precipitate as insoluble ferric phosphate
b. Removal of the dissolved inorganic matter is not standard treatment though it
is becoming more common
5. Final Clarification and Disinfection - eliminates pathogens
6. Discharge effluent to lake, stream, ocean
Fig. 18.11A Raw sewage moves from the grit chamber to primary treatment, where sludge is removed and the clarified water then proceeds to secondary treatment (here shown as activated sludge treatment).
Fig. 18.11B In primary treatment sludge is removed and the clarified water then proceeds to secondary treatment. Raw sewage moves from the grit chamber to primary treatment, where sludge is removed and the clarified water then proceeds to secondary treatment.
Fig. 18.11C Raw sewage moves from the grit chamber to primary treatment, where sludge is removed and the clarified water then proceeds to secondary treatment (here shown as activated sludge treatment).
Fig. 18.13 The secondary treatment, activated sludge process may be modified to remove nitrogen and phosphate while at the same time breaking down organic matter.
Fig. 18.16 Sewage treatment for a private home uses a septic tank and drain field. All the pipes and the tank are normally buried.
D. What Do We Do with the Sludge that Remains?
1. Most sludge is disposed of in landfills or spread on land
a. These practices are diminishing (but need more public pressure to continue)
·Sludge is difficult to handle in landfills
·Spreading can result in water pollution, and
·Sludge is nutrient rich organic material that can be used as organic
2. Several methods exist for treating sludge so that the pathogens are eliminated and it
is suitable as an organic fertilizer. (This assumes toxic contaminants are not present in
the sludge; industrial pretreatment and sustainable homeowner practices are
a. Anaerobic Digestion
E. Alternative Treatment Systems
1. Gray Water
2. Using Effluents for Irrigation
3. Reconstructed Wetland Systems (Eureka, California has a fully operational wetland
IV. Public Policy
A. The Landmark Clean Water Act and Reauthorization Needs