Wastewater Treatment Overview

Wastewater Treatment Overview

• Wastewater treatment is also known as sewage treatment or domestic wastewater treatment.
• It removes contaminants from wastewater, including runoff and domestic water.
• Goals include producing a waste stream (effluent), solid waste (sludge), and safely releasing these back into the environment.
• Sources of wastewater include residences (e.g., kitchens, bathrooms), commercial institutions, and industrial facilities (often requiring specialized treatment).
• Wastewater is collected and transported via pipes and pump stations to a municipal treatment plant.
• Wastewater treatment involves three main stages: primary, secondary, and tertiary.

Primary Treatment

• Primary treatment physically removes solids from wastewater.
• Typical materials removed during primary treatment include fats, oils, and greases (FOG), sand, gravel, rocks (grit), larger settleable solids, and floating materials.
• Methods used in primary treatment include:
  • Sand catchers remove sand and grit.
  • Controlling wastewater velocity ensures proper settling.
  • Settling tanks (Primary Sedimentation Tanks) are used to remove grease, oil, and settleable solids that rise to the surface
  • Separated solids are pumped to the sludge treatment plant.

Secondary Treatment

• Secondary treatment degrades dissolved organic matter.
• This is achieved by adding bacteria and protozoa to the sewage.
• Three secondary treatment approaches exist:
  • Fixed film systems: Microorganisms grow on substrates. Wastewater spreads over substrates like rocks, sand, or plastic
    • Examples include trickling filters and rotating biological contactors.
  • Suspended film systems: Microrganisms stir and suspend in wastewater. Solids settle to form sludge and are pumped back into incoming wastewater.
    • Examples include activated sludge and extended aeration.
  • Lagoon systems: Waste water is held for several months to allow for natural degradation. Plants like reeds are often used.

Tertiary Treatment

• Tertiary treatment removes disease-causing organisms.
• Three main methods of disinfection are used:
  • Chlorination (most common, low cost, but chlorine residue can harm the environment)
  • UV light radiation (no chemicals used, but high maintenance)
  • Ozonation (safer than chlorination, fewer disinfection by-products but high cost)

Sludge Disposal

• Sludge treatment aims to reduce odors, dewater the sludge and reduce its volume (decompose the organic matter).
• Primary sludge has strong odors; secondary sludge has high concentrations of microorganisms.
• Sludge is dewatered and often sold as fertilizer or spread on fields to save landfill space.
• Techniques like superheating and converting sludge into small granules and can help to make it less harmful.

Advanced Treatment

• Advanced treatments focus on removing nitrogen and phosphorus from the effluent, which can lead to eutrophication and algal blooms.
• Nitrogen removal involves converting ammonia to nitrite and then to nitrate.
• Phosphorus removal often uses precipitation with iron or aluminum salts.

Effluent Use

• Treated wastewater (effluent) can be discharged into streams, rivers, bays, lagoons, or wetlands.
• Effluent can also be used for irrigating golf courses, greenways, or parks.
• Clean effluent can be used for groundwater recharge.

Explore the key concepts of wastewater treatment in this quiz, covering the stages and processes involved in sewage treatment. Understand the sources of wastewater and the main removal techniques used in primary treatment. Test your knowledge on how contaminants are managed in the municipal treatment process.