Water Pollution Notes

Water Pollution

Nutrient Pollution

• Nitrates:
  • Typical levels: $0.1-4$ ppm (parts per million).
  • Unpolluted water: usually below $1$ ppm.
  • Sewage pollution can increase levels up to $20$ ppm.
• Phosphates:
  • Unpolluted water: usually below $0.1$ ppm.
  • In the 1990s, $40\%$ of streams had levels greater than $0.1$ ppm.

Sources of Water Pollution

• Water is polluted by:
  • Infectious bacteria.
  • Inorganic and organic chemicals.
  • Excess heat.
• Definition: Any chemical, biological, or physical change in water quality that has a harmful effect on living organisms.
• The World Health Organization (WHO) estimates that $3.4$ million people die prematurely each year from waterborne diseases.
• In the U.S., an estimated $1.5$ million people become ill each year from infectious agents.

Point vs. Non-Point Sources

• Point sources:
  • Discharge pollutants at specific locations through drain pipes, ditches, or sewer lines into bodies of surface water.
  • These sources are easy to identify, regulate, and monitor.
• Non-Point sources:
  • Scattered and diffuse and cannot be traced to any single site of discharge.
  • Examples: croplands, livestock feedlots.
  • Difficult and expensive to identify and control.

Leading Causes of Water Pollution

• Agriculture:
  • Erosion, overgrazing, fertilizers, and pesticides.
• Industrial facilities:
• Herbicide/pesticide run-off:
  • Chemical input from farms, homeowners, and businesses.
  • Can directly poison and kill aquatic plants and animals.
  • Biomagnification occurs.
  • Solutions:
    • Reduce use/grow organic.
    • Restrict the type and amount of chemical used.
    • Plant buffers to reduce run-off.
• Animal waste and Fertilizer run-off:
  • Excessive nutrient input (nitrogen and phosphorus).
  • Causes Eutrophication:
    • Algal blooms block sunlight from underwater plants.
    • Bacteria decompose and use an excessive amount of oxygen.
    • Carry pathogens such as bacteria and viruses.
  • Solutions:

Sewage Treatment Plants

• Filters out most, but not all, pollutants.
• Untreated sewage is discharged when treatment plants break down or become overloaded during heavy rain.
• Sewage contains excess nutrients, contributing to eutrophication.
• Contains many pathogens.

Septic Systems

• Ensure individuals with septic tanks have them pumped out regularly and disposed of properly.
• Protect natural wetlands and create artificial wetlands to help filter wastewater.
• Consists of a tank and a drain field.
• Wastewater enters the tank where solids settle out.

Wastewater Treatment (Point Source of Pollution)

• By law, wastewater treatment facilities can only release so many nutrients.
• Nitrates and phosphorus are released by treatment facilities.
• Medications and endocrine disruptors are not able to be processed by the plants.
• The wastewater system relies on gravity to move sewage from homes to the treatment plant.
• Wastewater-treatment plants are located on low ground, often near a river into which treated water can be released.

Preliminary/Primary Treatment Process

• Bar screens catch large objects that could harm equipment and pumps.
• Grit chambers settle dirt.
• Wastewater flow is slowed down, and suspended solids settle to the bottom of a settling tank by gravity.
• The material that settles is called sludge or biosolids.

Anaerobic-Aerobic Method (AO Method) - Phosphorus Elimination

• Involves a reaction tank, sedimentation in the first clarifier, and a waste tank.
• Diagram Description
  • Anaerobic tank > Aerobic Tank > The secondary clarifier > Disinfecting facility > Discharge water
  • Raw sludge > Sludge thickener tank > Stirring > Return sludge > Excess sludge > KENKI DRYER > Dewatering > Drying

Coagulation

• Occurs when a coagulant is added to water to "destabilize" colloidal suspensions.
• In a colloidal suspension, nanoparticles join together to form larger particles in liquids.
• Occurs naturally or artificially using alum in water.

Dealing with Sludge

• Sludge: the organic portion of sewage that settles out of the wastewater and is pumped out of the tanks.
• Some of the water is removed in a step called thickening.
• The sludge is processed in large tanks called digesters for $20-30$ days.
• Bacteria break down the material, reducing its volume, odors, and getting rid of disease-causing organisms.
• The resulting product is mainly sent to landfills but can sometimes be used as fertilizer.

Dealing with Scum

• Lighter materials float to the surface.
• This 'scum' includes grease, oils, plastics, and soap.
• Slow-moving rakes skim the scum off the surface of the wastewater.
• Scum is thickened and pumped to the digesters along with the sludge.

Secondary Treatment

• A biological process.
• Aeration:
  • Utilizes bacteria and algae to metabolize organic matter in the wastewater.
  • Exposing wastewater to air causes some dissolved gases to be released from the water.
• Wastewater enters a series of long, parallel basins.