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Chapter 11 Water Pollution

Two Primary Typesof Water Pollution

• Point Source Pollution - Pollutants released into the water from a discrete source, like out of the end of a pipe.

• Non-Point Source Pollution - Pollutants released from a diffuse source. Primarily caused by rainfall events washing pollutants off the surface of the land.

Kinds and Sources of Water Pollution

• Municipal water pollution– bacterial contamination– oxygen demand– Nutrients– Pharmaceuticals, Personal Care Products

• Industrial Water pollution– Same problems as municipal– Toxicants

Kinds and Sources of Pollution

• Agriculture– Pesticides– Nutrients – N & PNutrients N & P– Sediments– Temperature– Energy

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Kinds and Sources of Water Pollution

• Thermal pollution– Electrical power plants– Other types of industries

• Marine pollution– Debris– Oil– Hazardous wastes

Selected Water Pollutants• Biochemical Oxygen Demand - BOD

– The demand that bacteria have for oxygen to decompose organic matter in water

– It is usually measured in milligrams per liter of oxygen consumed in five days at 20°C … hence BOD5

Thi k f it f h h i tt i i– Think of it as a measure of how much organic matter is in the water.

• Raw sewage approximately 200 mg/L• Very clean surface water 1 mg/L• Indication of pollution 10 mg/L

BOD and Dissolved Oxygen• As BOD increases, Dissolved oxygen (DO) decreases.• Example: Raw sewage into stream

– Unpolluted head water: High DO, Low BOD– Pollution zone : Low DO, high BOD

Active decomposition zone : Low DO reducing BOD– Active decomposition zone : Low DO, reducing BOD– Recovery Zone : Increasing DO, Lower BOD– Unpolluted water: High DO, Low BOD

Fecal Coliform Bacteria• Pathogenic bacteria like cholera and typhoid are

difficult to detect• Use an indicator organism - human fecal coliform

bacteria– Harmless bacteria in human intestine

If lif t th t h th– If coliforms are present, the water may have pathogens• If no fecal coliforms are found, the water will likely

not contain pathogens - Criteria is 200 fecal coliforms / 100ml

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Nutrients -Nitrogen and Phosphorus

• Concentrations of N and P in surface water is often a function of land use.– Forest - low N and P

Agriculture High N and P– Agriculture - High N and P• Increased nutrients accelerates

eutrophication– Oligotrophic : Young, nutrient poor– Eutrophic : old, nutrient rich

Nutrients -Nitrogen and Phosphorus

• Typically want water to have – N between 1 and 2 mg/L– P between 0.05 and 0.1 mg/LP between 0.05 and 0.1 mg/L

• Many states have banned the use of phosphate detergents

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Heavy Metals• A metal of atomic weight greater than sodium

(22.9)• Examples : mercury, zinc, cadmium• Often adsorb to soil particles and become

deposited with sediment in bottoms of streams anddeposited with sediment in bottoms of streams and floodplains

• Potential exists for heavy metals to be incorporated into crops if floodplains are used for agriculture

Thermal Pollution

• Primarily from hot-water emissions from industries and power plants

• Warm waters favor certain speciesp– Thermophillic - like it hot– Stenophillic - narrow range of tolerance– Euryphillic - large range of tolerance– Stenohaline / euryhaline– WARM WATER HOLDS LESS OXYGEN!

Sediments and Sedimentation

• Small rocks and mineral fragments that enter into a body of water

• If fragments enter water at a rate greaterIf fragments enter water at a rate greater than under natural conditions, sediment is considered a pollutant.

• By volume, sediments are by far our greatest pollutant.

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Land Use and Sedimentation

• Natural surfaces like forests and pastures hold soils together very well

• Clear cutting releases large amounts of soilClear cutting releases large amounts of soil. – Streams may fill with sediment– Ecological and hydrological impacts follow.

Land Use and Sedimentation

• Cropping releases moderate amounts of soil. Streams partially fill and become muddy.y

• Urbanization prevents much erosion (parking lots, impervious cover) but causes flooding.

Toxicants

• Pesticides- atrazine• Pharmaceuticals• Estrogen mimicking compounds• Estrogen mimicking compounds• Hydrocarbons – MTBE• Persistent organic compounds – dioxin,

PCBs• Oil

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Water Treatment

• Safe Drinking Water Act of 1974, 1977 states that water used by the public must meet certain quality requirements q y q(Maximum Contaminant Levels or MCLs)

• Remove water, coagulate particles, filter particles, chlorinate water, test water for quality, distribute to public

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Waste Water Treatment• Clean Water Act of 1977 states that wastes

discharged to the environment must meet certain water quality requirements (Primary and Secondary Standards - Water Quality Criteria

• Collect water, settle large solids, use microbial action to degrade organics - activated sludge, coagulate impurities, chlorinate water to disinfect, de-chlorinate and test water. Distribute.

Waste Water Treatment• Primary Treatment - Screen then settle.• Secondary Treatment - put in oxygenated

environment, microbes eat organic matter, microbes produce sludge– Trickling filters versus activated sludge

• Tertiary treatment– Chlorinate / Dechlorinate– Possible other treatments … wetlands

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