Waste Water


EVER WONDER …?

How waste water is made safe to re-enter the environment?

The purpose of treating waste water is to remove contaminants in order to return the water back into the environment. In order to accomplish this waste water treatment plants employ 3 levels of treatment (primary, secondary and tertiary) in various combinations to remove physical, chemical and biological contaminants. The treatment process is multi-stepped.

Waste Water = Storm Drain Runoff + Sewage

Waste Water is Collected
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Primary Filtration

  • Removes large materials (eg. Plastic bags, sticks, tennis balls search description

Detritor (sand catcher)

  • Removes sand and grit from the waste water
  • Speed or velocity of the water is carefully controlled allowing sand grit and stones to settle on the bottom
  • This stage is necessary to prevent damage to water pumps later in the process search description

Sedimentation (Primary Clarifiers)

  • Solids sink to the bottom of the tank
  • Other materials such as grease and oils float to the top.
  • Both the top and bottom are skimmed to remove these organics and they are sent to digesters where they undergo anaerobic decomposition with the byproduct being used as a fuel and as a fertilizer search description

Activated Sludge

  • Dissolved oxygen is used to promote the growth of biological “floc” which removes the organic material from the water search description

Membrane Biological Reactors

  • Combines activated sludge with a membrane liquid-solid separation process
  • Uses low pressure micro-filtration or ultra-filtration to remove both soluble and particulate biodegradable materials search description

Secondary Sedimentation

  • Allows for settlement of the biological “floc” or filtered material. The byproduct is again sent to the digesters to undergo anaerobic decomposition search description

Filtration

  • Sand filters are the most common form, other types include activated carbon which removes residual toxins.
  • Filtration removes items based on size search description

Disinfection

  • Reduces microorganisms through chlorination, ultraviolet radiation and ozone treatment
  • Chlorination and ozone both oxidize pathogens and biologic materials still found in the water
  • UV radiation causes damage to the genetic material in bacteria and protozoa, inactivating them and making them harmless search description

Lagoons

  • Highly aerobic environment contains small filter feeders such as Daphnia and Rotifera that remove fine particles
  • Lagoons also help to further settle any particles that may still be floating in the water