Environmental Science: Toward a Sustainable Future Richard T. Wright

Water Pollution and Its Prevention

PPT by Clark E. Adams

Chapter 17

Water Pollution and Its Prevention

• Water pollution• Eutrophication• Sewage management and

treatment• Public policy

Pollution

• Pollution: “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 health effects.”

Water Pollution

• Pollution essentials• Water pollution: sources, types,

criteria

Pollution Categories

• Air• Particulates• Acid-forming compounds• Photochemical smog

• CO2

• CFCs

Pollution Categories

• Water and land• Nutrient oversupply• Solid wastes• Toxic chemicals• Pesticides/herbicides• Nuclear waste

Water Pollution Types

• Pathogens• Organic Wastes• Chemical• Sediments• Nutrients

Pathogens Carried by Sewage

• Disease-causing agents (Table 17.1)

• Safety measures• Purification of public water supply• Sanitary collection/treatment of

sewage• Sanitary practices when processing

food

Organic Wastes

• Dissolved oxygen (DO) in the water is depleted during decomposition of organic wastes.

• Water quality test•Biochemical oxygen demand

(BOD): measure of the amount of organic material.

Testing Water for Sewage

Fecal Coliform Test

Chemical Pollutants

• Inorganic chemicals•Heavy metals, acids, road salts

• Organic chemicals •Petroleum, pesticides,

detergents

Effect of Sediments on Stream Ecology

• Loss of hiding/resting places for small fish

• Attached aquatic organisms scoured from the rocks and sand

• Poor light penetration

Eutrophication

• Different kinds of aquatic plants• The impact of nutrient enrichment• Combating eutrophication

Different Kinds of Aquatic Plants

• Benthic plants•Emergent vegetation•Submerged aquatic vegetation

(SAV)

Different Kinds of Aquatic Plants

• Phytoplankton•Green filamentous and single cell•Blue-green single cell•Diatoms single cell

The Impacts of Nutrient Enrichment

• Oligotrophic: nutrient-poor water• Eutrophic: nutrient-rich water

What kind of plants would dominate in oligotrophic vs. eutrophic conditions?

Eutrophication

• As nutrients are added from pollution, an oligotrophic condition rapidly becomes eutrophic.

Oligotrophic

Eutrophic

Eutrophic or Oligotrophic?

• High dissolved O2

• Deep light penetration• High phytoplankton

Eutrophic or Oligotrophic?

• Turbid waters• High species diversity• Good recreational qualities• High detritus decomposition

Eutrophic or Oligotrophic?

• Low bacteria decomposition• Benthic plants• Warm water• High nutrient concentration• BOD• High sediments

Natural and Cultural Eutrophication• Natural eutrophication

• aquatic succession• occurs over several hundreds of years

• Cultural eutrophication• driven by human activities• occurs rapidly

Combating Eutrophication

• Attack the symptoms• Chemical treatment• Aeration• Harvesting aquatic weeds• Drawing water down

Combating Eutrophication

• Getting at root cause• Controlling point sources• Controlling nonpoint sources

Controlling Point Sources

• Ban phosphate detergents• Sewage-treatment improvements

Controlling Nonpoint Sources

• Difficult to address runoff pollutants•Urban•Agricultural fields•Deforested woodlands•Overgrazed pastures

Controlling Nonpoint Sources

• Best Management Practices (BMP): Table 17-2•Agriculture•Construction•Urban

Sewage Management and Treatment

• Development of sewage collection and treatment systems

• The pollutants in raw sewage• Removing the pollutants from

sewage• Treatment of sludge• Alternative treatment systems

Development of Sewage Collection and Treatment Systems• Storm drains for collecting runoff

from precipitation• Sanitary sewers to receive all the

wastewater from sinks, tubs, and toilets

Development of Sewage Collection and Treatment Systems• Through the 1970s sewage was

discharged directly into waterways• Clean Water Act of 1972

Pollutants in Raw Sewage

• 99.9% water to 0.1% waste• Pollutants in sewage are:

• Debris and grit• Particulate organic material• Colloidal and dissolved organic

material• Dissolved inorganic material

Removing Pollutants from Sewage: Match Technology with FunctionTechnology Function

Bar Screen Particulate organics

Grit Screen Dissolved organics

Primary Treatment Dissolved inorganics

Secondary Treatment

Large or small debris

Trickling Filters for Secondary Treatment

Trickling Filters for Secondary Treatment

Biological Nutrient Removal

• Activated sludge: 3 zones

• Conversion of NH4 to NO3

• NO3 converted to N gas and released

• PO4 taken up by bacteria and released with excess sludge

Sludge Treatment

• Anaerobic digestion• Composting• Pasteurization

Treatment of Sludge

MethaneHumus

Alternative Treatment Systems

• Individual septic systems• Wastewater effluent irrigation• Reconstructed wetland systems

• Beaumont, TX

• The waterless toilet

• Aerobic digestion of solids in septic tank

• Flow of liquids into drain field for evaporation, infiltration, or irrigation

Septic Tank Treatment

Public Policy

• What was the legislative milestone in protecting natural waters and water supplies for each of the acts listed in Table 17-3?

End of Chapter 17