Water PollutionPollution: “the presence of a substance in the (aquatic)

environment that because of its chemical composition or quantity prevents the functioning of natural processes and produces undesirable environmental and health effects.”

• Pathogens• Organic Wastes• Chemical• Sediments• Thermal• Nutrients

Point Source versusNon-point Sources of Pollution

Pathogens• Disease-causing agents (Table 18.1) • Safety measures

– purification of public water supply– sanitary collection/treatment of sewage– sanitary practices when processing food– Frequent testing of indicator microorganisms

Organic Wastes• Dissolved oxygen (DO) in the water is depleted

during decomposition of organic wastes (caused by microbial respiration)

• Water quality test. – Biochemical oxygen demand (BOD):– More organic material; higher BOD.– A goal of sewage water treatment is to reduce

BOD.• High BOD may cause fish kills.• High BOD waters produce noxious odors (stinky)

Chemical Pollutants• Inorganic chemicals

– Heavy metals – Acids – Road salts

• Organic chemicals – Petroleum– Pesticides– Detergents

Excess Sediments on Stream Ecosystems

• Caused by soil and stream bank erosion.• Loss of hiding-resting places for small fish

and macroinvertebrates.• Clog fish gills and may cause infections.• Attached plants, algae and

macroinvertebrates get scoured from the rocks by sands.

• Poor light penetration reduces primary production for the ecosystem.

• Costly to remove in water treatment plants.

Nutrient Enrichment

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

• Mesotrophic: nutrient-moderate water

What kind of algae or plants would dominate in oligotrophic and 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• Turbid waters• High species diversity• Good recreational

qualities• High detritus

decomposition• Benthic plants

Nutrient Inputs

Nutrient Inputs

Natural Vs. Cultural Eutrophication

• Natural eutrophication– aquatic succession– occurs over several hundreds of years

• Cultural eutrophication– driven by human activities– occurs rapidly

Controlling Non-point Sources

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

• Best Management Practices (BMP)– Urban & Suburban Development– Agricultural

BMP e.g.: Collecting Ponds

Control Point SourcesWastewater Treatment

• 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– Human Pathogens– Toxic Chemicals– Pharmaceuticals

Wastewater Treatment

• Preliminary (physical screening)• Primary (physically settle solids)• Secondary (biological solids production) • Tertiary (biological or chemical “polishing”)

– Biological nutrient removal systems– Pathogen removal by chlorine or ozone– Chemical nutrient removal (costly)

• Sludge Treatment (solids reduced)

Wastewater Treatment

Anaerobic Sludge Digester

(Methane and Cogeneration)

Alternative Treatment Systems

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

– Beaumont, TX• The waterless toilet