8.11 Sewage Treatment Processes and Contaminants

Overview of Sewage Treatment Processes

Context of Bacteria in Waste Treatment

  • Bacteria Role: Bacteria are utilized in various treatment processes to help break down organic matter in sewage, effectively eating the organic materials present in waste.

Types of Contaminants Found in Water

  • Contaminants: Three contaminants typically found in water bodies, particularly affected by agricultural runoff and sewage discharge, include:

    • Nitrogen

    • Phosphorus

    • Pathogens, such as E. coli

Sewage Treatment Process (Hantrent Process)

1. Primary Treatment

  • Objective: Physical removal of large debris from wastewater.

  • Methods Used:

    • Use of screens or grids to filter out solid materials and debris before further treatment.

2. Secondary Treatment

  • Objective: Biological breakdown of organic materials in wastewater.

  • Process Characteristics:

    • This treatment is an aerobic process, meaning it requires oxygen ($O_2$) to facilitate the breakdown through microbial action, particularly by bacteria that consume organic matter.

3. Tertiary Treatment

  • Objective: Further treatment after primary and secondary to remove additional contaminants.

  • Methods:

    • Can involve ecological or chemical processes aimed specifically at eliminating excess nitrogen (N), phosphorus (P), and bacteria.

    • This phase often employs chemical filters and similar treatments to assure the water is cleaner before being released back into the environment.

Disinfection Methods

  • Objective: To kill pathogens present in treated water.

  • Methods Used:

    • UV Light: Utilizes ultraviolet light to kill bacteria and viruses.

    • Ozone Treatment: Ozone ($O_3$) helps sterilize water through oxidation.

    • Chlorination: Chlorine is often used to disinfect by killing harmful microorganisms.

Definitions and Key Terms

  • Effluent: Refers to the liquid waste (sewage) that is discharged into water bodies, typically released from a wastewater treatment plant after treatment.

  • Sludge: Refers to the inorganic and organic solid waste that settles at the bottom of the treatment tank during the secondary treatment phase.

  • Pumping and Treatment: Sludge is spun or pumped off; remaining physical waste is then dried and collected to be converted into fertilizer pellets for agricultural use.

The release of untreated or raw sewage into surface waters can lead to serious environmental problems, including:

  • Water Pollution: Raw sewage contains harmful pathogens, nutrients, and chemicals that contaminate water bodies, making them unsafe for aquatic life and human use.

  • Eutrophication: High levels of nutrients such as nitrogen and phosphorus from sewage can lead to excessive plant growth (algal blooms), which deplete oxygen in the water, harming aquatic organisms.

  • Habitat Degradation: Contaminants can alter physical and chemical properties of water bodies, leading to habitat loss for many aquatic species.

  • Health Risks: The presence of pathogens can pose a significant health risk to humans and animals, leading to diseases related to waterborne infections.

  • Biodiversity Loss: Polluted waters can result in lower biodiversity as sensitive species are unable to survive in the contaminated environment.

  • Fishery Impacts: Contamination can negatively affect fish populations and other aquatic life, disrupting local fishing industries and ecosystems.