This how it works covers How It Works: Sewage Treatment Stages within Water Treatment for GCSE Chemistry. Revise Water Treatment in Using Resources for GCSE Chemistry with 23 exam-style questions and 15 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 5 of 14 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
🚽 How It Works: Sewage Treatment Stages
Sewage (wastewater) from homes and businesses must be cleaned before returning to environment:
- Primary Treatment (Physical):
- Screening — large objects removed (rags, plastic)
- Settling tanks — solids sink to form sludge
- Removes ~60% of suspended solids
- Secondary Treatment (Biological):
- Activated sludge process — bacteria break down organic matter
- Air pumped in to keep bacteria alive (aerobic respiration)
- Further settling tanks separate clean water from bacteria
- Removes ~90% of organic matter and pathogens
- Tertiary Treatment (Chemical - HT only):
- Advanced filtration and disinfection
- UV light or ozone to kill remaining pathogens
- Nutrient removal (nitrogen and phosphorus)
- Produces high-quality effluent safe for environment
Sludge treatment: The solid waste (sludge) is digested by bacteria to produce methane gas (used for energy) and compost for agriculture.
Practice questions for Water Treatment
What does the term 'potable water' mean?
Explain what happens to the sewage sludge produced during waste water treatment, and why this process is useful.