Waste Water Treatment

Water Use

  • Humans use a large amount of water:

    • Drinking (small percentage).

    • Personal hygiene (baths, showers).

    • Flushing toilets.

    • Washing clothes.

    • Agriculture.

  • Wastewater contains:

    • Organic molecules (e.g. from human waste).

    • Harmful microorganisms (e.g. bacteria).

  • Must be treated before being released into the environment.

Sewage Treatment Process

  1. Screening

    • Sewage passed through a mesh.

    • Removes solids and grit.

  2. Sedimentation

    • Sewage left to settle in large tanks.

    • Produces:

      • Liquid effluent.

      • Sludge (semi-solid, sinks).

  3. Sludge treatment

    • Broken down by anaerobic bacteria (no oxygen).

    • Produces biogas → can be burned for electricity.

    • Digested sludge can be used as fertiliser.

  4. Liquid effluent treatment

    • Contains organic molecules + harmful microbes.

    • Air bubbled through → aerobic bacteria digest organic matter and microbes.

    • After treatment, water can be discharged into rivers or the sea.

Industrial Wastewater

  • Used in industry (e.g. making paper, chemicals).

  • Must first have harmful chemicals removed.

  • Then joins general sewage treatment.

Comparing Water Sources for Potable Water

  • Groundwater (aquifers)

    • Easiest source for potable water.

    • Usually safe after chlorine treatment.

    • Can sometimes be polluted (e.g. fertilisers).

  • Wastewater (sewage)

    • Can be turned into potable water.

    • Requires many purification steps.

    • Only used where water is scarce.

  • Salt water (seawater)

    • Requires desalination.

    • Needs lots of energy and is expensive.

✅ Key Idea:

  • Wastewater must be treated to remove solids, organic matter, and microbes.

  • Methods depend on the source: aquifers (easiest), wastewater (harder), seawater (most energy-intensive).