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:
Screening to remove debris.
Addition of coagulants for easier sedimentation.
Filtration to clear remaining impurities.
pH correction, anti-corrosion agents to protect water quality.
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.