Sources of Waste Water

  • Water is used on a daily basis in a domestic environment. For example, washing-up dishes, showers and baths and cooking.
  • When you run water down a drain, it passes through sewers and then finally to sewage treatment plants.
  • Regarding the agricultural industry, waste from animal farms and nutrient run-off which is collected from fields produce an abundance of waste water.
  • Both domestic and agricultural sewage needs to be processed to filter any harmful bacteria and microbes.
  • This can then be safely returned to freshwater sources i.e. lakes and rivers.
  • If this process did not take place, it could potentially pose health risks for the population.
  • Waste water that is produced by the Haber process and other industrial processes needs to be gathered and treated appropriately.
  • Harmful chemicals and organic matter are present in industrial waste.
  • This therefore means that additional treatment has to be in place to ensure it is safe for the environment.

Obtaining Potable Water by Treatment

  • Screening & Grit Removal
    • The first stage of treatment removes large materials such as plastic bags and twigs and grit by screening.
  • Sedimentation
    • Sedimentation comes next which occurs in a settlement tank. The water is allowed to stand still in the tank while heavier solids sink to the bottom creating a sludge, whilst lighter matter which is also known as effluent, floats to the top.
  • Aerobic Digestion
    • The effluent is removed and treated by biological aerobic digestion.
    • This involves pumping air into the water to encourage the breakdown of organic matter and other microbes by aerobic bacteria.
  • Anaerobic Digestion
    • Anaerobic digestion is then used to break down the sludge from the bottom of the settlement tank. It is firstly removed and placed in large tanks where bacteria break it down.
    • Anaerobic digestion releases methane gas as a by product from the organic matter in the sludge. Methane gas is used as a source of energy and the leftover, digested waste as a fertiliser.

Waste-Water-Treatment---AQA, IGCSE & GCSE Chemistry revision notes

Diagram showing the stages of waste water treatment

  • When there are toxic substances within waste water, it is important to use additional phases of treatment.
  • This can include using membranes, adding additional chemicals e.g. to precipitate metals out of solution, and also U.V. radiation.
  • Sewage water is often treated in areas where there is little freshwater available.
  • Though this process is longer than processing and preparing freshwater, it uses less energy than the desalination of salt water.

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.