How It Works: Sewage Treatment Stages
Part of Water Treatment — GCSE Chemistry
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 20 exam-style questions and 15 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 4 of 13 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 13
Practice
20 questions
Recall
15 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.