8.11-8.13 APES notes

Topic 8.11: Sewage Treatment

Best Practices in Sewage Treatment

  • Focus on efficient sewage treatment processes to minimize environmental impact and maintain public health.

Water Flow in Sewage Systems

  • Sewer systems (City sewer): Channel wastewater to treatment facilities rather than employing septic systems.

Water Treatment Process

  • Stages of Treatment:

    1. Primary Treatment: Initial phase for physical removal of solids.

    2. Secondary Treatment: Biological breakdown of organic materials.

    3. Tertiary Treatment: Advanced purification to eliminate remaining pollutants.

Detailed Stages in Sewage Treatment

  • Primary Treatment:

    • Process: Screening to filter debris (e.g., plastics, leaves, sticks).

    • Objective: Allow sedimentation to settle solid waste and separate lightweight materials.

  • Secondary Treatment:

    • Process: Involvement of microbes in decomposing organic matter (e.g., fecal matter, ammonia).

    • Removal Efficiency: Approximately 70% of phosphorus (P) and 50% of nitrogen (N) removed, but Persistent Organic Pollutants (POPs) remain.

    • Environmental Impact: Aimed to reduce nutrient pollution, which can trigger cultural eutrophication.

  • Tertiary Treatment:

    • Methods: May utilize both ecological and chemical processes that chemically treat water.

    • Disinfection Techniques: Use of UV light, ozone, or chlorine to eliminate harmful pathogens (e.g., E. coli).

Sewage Treatment Process Flow

  1. Wastewater transported via underground pipes to treatment plant.

  2. Large debris screened and disposed of in landfills.

  3. Solid waste settles in tanks, forming sludge.

  4. Aeration promotes bacterial activity converting organics into CO2 and inorganic nutrients.

  5. Sludge managed through thickening and removal: incineration, landfill, or use in fertilizers.

  6. Disinfection via ultraviolet light or chemicals to kill remaining pathogens.

  7. Treated water released into nearby waterways (rivers, lakes).

Water Quality Monitoring

  • Conducted at each treatment stage to ensure compliance.

  • Legislation Impact:

    • Clean Water Act (CWA): Establishes standards for wastewater discharge.

    • Safe Drinking Water Act (SDWA): Ensures quality of drinking water and mandates permits for discharges.

    • Funding aid for water treatment infrastructure improvements.

Sewage Treatment Issues

  • Combined Sewage and Storm Water Systems: Risk of overflow during heavy rain, which can lead to untreated wastewater entering waterways.

  • Environmental Concerns of Overflow: Potential introduction of pathogens, ammonia, nitrates, and phosphates into local water systems.

  • Even treated water can have elevated nutrient levels and endocrine disruptors.

Topic 8.12: Lethal Dose 50% (LD50)

Definition of LD50

  • Lethal Dose 50% (LD50): The specific dose of a chemical that causes death in 50% of a given population (typically of a particular species).

Application of LD50 and ED50

  • Example: Comparison involving tarantulas and their prey.

  • Median Effective Dose (ED50): Measure of the dose that achieves a therapeutic effect in 50% of the population; synonymous with sublethal dose.

ED50 and Dose-Response Relationships

  • Definition: Broad application in assessing responses to various stimuli, including drugs and environmental factors.

  • The concept extends to fields like epidemiology for risk assessment and materials science for testing strength.

  • Any measurable effect in an organism can form a basis for constructing dose-response curves.

Topic 8.13: Dose Response Curve

Overview of Dose Response Curves

  • A tool to represent the relationship between the dose of a substance and its effect on organisms or mortality rate within a population.

  • Graphical Representation:

    • Typically plots dose on a logarithmic scale against the percentage of the population responding to the treatment.

Example of a Dose Response Curve

  • Visualization of effects at varying doses from 0 to 10000, displaying the mortality rate, with a notable point at LD50 indicating 50% response.

Chemical Production and Environmental Impact

Industries Contributing to Pollution

  • Major Industries:

    • Petroleum, paper production, soap, fertilizers, pesticides, paints, dyes, pigments.

Heavy Metal Pollution Sources

  • Sources of Heavy Metal Contamination:

    • Mining, metallurgy (including electronics, jewelry, and mineral processing).

    • Associated problems such as electroplating and wastewater management leading to bioaccumulation in aquatic food chains.

  • Impact on Ecosystems and Human Health:

    • Heavy metals present risks including cancer and organ damage, primarily affecting fish populations and subsequently, human health through consumption of contaminated seafood.

Ethical Considerations in Dose-Response Research

Use of Model Organisms

  • Due to ethical constraints preventing testing on humans, model organisms (e.g., mice and rats) are employed to gather data regarding potential human effects.

  • Types of Studies:

    • Acute Studies: Evaluate immediate impacts in isolated scenarios but may not reflect ecological relationships.

    • Chronic Studies: Assess long-term effects of substances on adult organisms.