APES 8.11 Sewage Treatment

Septic Systems

• Functionality: Wastewater from toilets goes to a septic tank, which maintains a constant level of waste.

• Components:

  • Scum: The layer of fats and oils that floats on the surface.

  • Sludge: The solid waste that settles at the bottom.

  • Effluent: Clear water that exits the septic tank.

• Process: Waste is broken down and pumped out approximately every two years. The effluent flows into a leach field for further filtration.

Sewage Treatment Plants

• Definition: Centralized systems in large municipalities designed for wastewater treatment.

Primary Treatment

• Description: Physical removal of solid objects.

• Methods:

  • Use of screens and grates to filter out debris.

  • Settling tanks where waste collects at the bottom.

  • Removal of sewage sludge to reduce further processing needs.

Secondary Treatment

• Description: Biological treatment involving aerobic bacteria.

• Process:

  • Aeration tanks where oxygen is added to stimulate bacterial growth.

  • Bacterial breakdown of waste into carbon dioxide and inorganic sludge.

  • Multiple rounds of stirring sewage to promote effective treatment.

Tertiary Treatment

• Definition: Final disinfection and treatment before water is released.

• Methods:

  • Use of chlorine, ozone, or UV light for disinfection (laboratory experiments may involve bleach).

  • Final chemical adjustments and the use of additional filters before reuse.

Water Treatment for Drinking

• Stages:

  1. Screening to remove debris.

  2. Addition of coagulants for easier sedimentation.

  3. Filtration to clear remaining impurities.

  4. pH correction, anti-corrosion agents to protect water quality.

  5. Chlorination and fluoride addition before distribution.

Environmental Concerns

• Heavy rains and floods can lead to overflows, causing plants to dump raw sewage into waterways; a significant issue in places like Indianapolis.

Sewage Lagoons

• Description: Man-made outdoor basins designed for the treatment of animal waste through anaerobic respiration.

• Context: Often associated with Concentrated Animal Feeding Operations (CAFOs), questioning their sustainability and impact on the environment.