Waste Water Treatment

Wastewater is water that has been contaminated and must undergo treatment before being released into other bodies of water. If not treated, wastewater can lead to further contamination. Anything that is flushed down the toilet or rinsed down the drain is considered wastewater. However, wastewater can also come from other sources, such as agriculture.

Rainwater and runoff, which may contain various pollutants, are channelled to wastewater treatment facilities through street gutters. Farms can also produce a large amount of wastewater. This agricultural waste also contains pesticides and fertilisers.

Both domestic and agricultural wastewater require treatment before being reintroduced to freshwater sources. However, agricultural wastewater is more difficult to treat than domestic wastewater. This is because it often contains higher levels of pollutants, such as pesticides, fertilisers, and animal waste, which are more challenging to remove. Agricultural wastewater is also typically spread over a larger area.

Consequences of Wastewater Pollution

If wastewater is not handled properly, it can harm the environment and many living organisms. Some of these negative impacts include:

  • Endangering fish and wildlife populations by introducing harmful substances into their habitats.
  • Depleting oxygen levels in water bodies, so many aquatic organisms cannot survive.
  • Causing beach closures and other recreational water usage limits, due to contamination risks.
  • Contaminating drinking water sources, making them unsuitable for human consumption.

Sewage Treatment

The sewage treatment process includes the following steps:

1. The sewage either flows or is pumped to a treatment facility.

2. During the screening and grit removal process, large materials like leaves and silt are removed.

3. During sedimentation, sewage settles in large tanks. This allows heavier solids to sink to the bottom and form sewage sludge. The lighter liquid that remains at the top is called effluent.

4. Anaerobic bacteria digest the sludge, producing biogas that can be burned to generate electricity. The digested sewage sludge can also be used as fertiliser.

5. Aerobic bacteria treat the effluent by digesting organic molecules within the water. This process involves pumping air into an aeration tank to facilitate bacterial digestion (aeration).

6. Once treated, the effluent is released into the sea or nearby rivers.

An isometric illustration of a sewage treatment plant process. Starting from "Your Home", waste travels through a "Collection System" into a "Pump Station". It then passes through "Screens" and goes towards "Grit Removal". From there, the waste enters the "Digester", followed by the "Sedimentation Tank", and then the "Trickling Filter". Subsequently, the waste flows into an "Aeration Tank", followed by a "Clarifier". The treated water then undergoes "Ultraviolet Disinfection" before being released as "Treated Wastewater". Concurrently, "Trash and Sand" are directed "to the Landfill", and "Biosolids" are also produced in the process. The background features a clear sky with a bright sun and some scattered trees around the facility.

For wastewater containing toxic substances, additional treatment stages may be necessary, such as:

  • Trickling filters – These remove organic matter from wastewater.
  • Clarifiers – Designed for continuous removal of solids from the water.
  • Ultraviolet radiation – Used to disinfect the effluent, ensuring it is safe for release into the environment.

You’ve used 10 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up