Strategies to Improve Water Quality (Cambridge (CIE) IGCSE Environmental Management): Revision Note

Improved sanitation

• Water quality improves when pollutants are reduced before they enter rivers, lakes or groundwater

  • Key strategies include better sanitation, effective sewage treatment and strong pollution control laws

  • These strategies protect both human health and aquatic ecosystems

• Improved sanitation includes the use of facilities that separate human waste from human contact

  • Reduces the spread of pathogens into water sources

• Flush toilets are connected to safe sewage systems

  • They move waste away from homes and reduce contamination of wells and streams

• Pit latrines with sealed pits

  • Prevent human waste leaking into surface water

  • Suitable where no sewer network exists

• Composting toilets

  • Use dry material to break down waste safely, producing compost

  • Reduce water use and contamination risk

• Good sanitation:

  • Prevents diseases such as cholera, dysentery and diarrhoea

  • Keeps drinking water supplies safer for communities

Treatment of sewage

• Sewage treatment is the process of removing harmful substances from wastewater so it can be:

  • Safely returned to the environment

  • Used for domestic purposes (e.g. for toilets, showers, drinking water)

• It prevents pollution, protects public health, and helps conserve water by recycling treated water

The three stages of sewage treatment

Primary treatment

• Purpose: Removes large solid materials (e.g. debris) and some suspended solids

• Process:

  • Screening: Large objects like sticks, rubbish, and plastic are filtered out using screens (usually made from metal bars)

  • Comminution: Any remaining large solids are ground up by a device called a comminutor to prevent pipe blockages

  • Grit removal: Sand and gravel settle to the bottom of the grit chamber

  • Sedimentation: Wastewater flows into sedimentation tanks (also known as primary clarifiers), where smaller suspended solid particles settle at the bottom as sludge

  • Skimming: Floating materials like grease and oil are skimmed from the surface

• Result: Water is partially cleaned but still contains dissolved and smaller particles

Secondary treatment

• Purpose: Breaks down organic matter using biological processes

• Process:

  • Aeration: Oxygen is pumped into the wastewater to encourage bacteria to break down organic pollutants (e.g. human waste, food)

  • Biological degradation: Microorganisms (mainly bacteria) consume the organic waste, converting it into harmless by-products like carbon dioxide, water, and 'activated sludge'

    • Activated sludge contains aerobic bacteria that decompose organic matter

  • Clarification: Water is again left to settle (in a secondary clarifier) so that any remaining sludge can be removed

    • A portion of this sludge is reused as activated sludge in the aeration tank to continue the process of organic matter decomposition

• Result: Water is significantly cleaner but may still contain some nutrients (e.g. nitrates, phosphates) and pathogens

Tertiary treatment

• Purpose: Removes remaining nutrients, chemicals, and pathogens for maximum water quality

• Process:

  • Chemical treatment: Chlorine or ultraviolet light (UV) is used to disinfect the water and kill pathogens

  • Nutrient removal: Processes like chemical precipitation are used to remove excess nitrogen and phosphorus, which can cause eutrophication if released into water bodies

  • Filtration: Water may be filtered through sand, activated carbon, or other materials to remove any final impurities

• Result: Effluent (treated water) is now clean enough to be safely discharged into rivers and lakes or reused

Pollution control & legislation

• Governments introduce rules to reduce pollutants entering air and water

Reducing acid rain pollutants

• Cutting emissions of sulphur dioxide and nitrogen oxides reduces acid rain

  • Achieved by reducing fossil fuel use in electricity generation and transport

• Using low-sulphur fossil fuels

  • Produces less sulphur dioxide during combustion

• Clean Air Acts encourage industries and power stations to adopt these practices

Monitoring and enforcing pollution limits

• Legislation may require companies to measure pollution levels from factories or wastewater discharge

  • Keeps pollution within safe limits

• There may be fines or legal penalties for exceeding limits

  • This encourages companies to reduce emissions or improve waste treatment

• In extreme cases, companies can be prosecuted or forced to shut down

Incentives for reducing pollution

• Governments may offer grants or tax relief for organisations that successfully reduce pollution

  • This encourages investment in cleaner technology

  • Supports industries transitioning to sustainable practices