AdvancedTopic 82 of 112Civil & Structural
Wastewater treatment
Primary, secondary and tertiary processes remove solids, organics and nutrients.
In depth
Primary treatment removes solids; secondary (activated sludge, trickling filter) biologically oxidises organics (BOD); tertiary removes nutrients and pathogens. Sludge is digested and dewatered. Effluent standards limit BOD, TSS, N and P. Anaerobic digestion yields biogas.
Key points
- BOD₅ test
- Aeration tank design
- Membrane bioreactors
ExampleAn activated sludge plant reduces BOD by over 90%.
Wastewater treatment protects rivers and public health, so each stage must remove solids, organic matter and nutrients to permitted levels.
What is Wastewater treatment?
Primary, secondary and tertiary processes remove solids, organics and nutrients.
Why is it important to understand wastewater treatment?
Wastewater treatment protects rivers and public health, so each stage must remove solids, organic matter and nutrients to permitted levels.
What does primary treatment remove?
Floating and settleable solids, which reduce the load on later stages and protect downstream processes.
What does secondary treatment do?
Biological processes remove dissolved and fine organic matter, usually with activated sludge or biofilm reactors.
How is Wastewater treatment used in practice?
Typical applications include designing a primary settling tank for a town sewage works, choosing an activated sludge process for a secondary treatment plant and upgrading a works to remove nitrogen and phosphorus for a sensitive river.
What should I learn before Wastewater treatment?
Study "Water distribution networks" first (topic 81 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Wastewater treatment?
BOD₅ test. Aeration tank design. Membrane bioreactors.
Can you give an example of Wastewater treatment?
An activated sludge plant reduces BOD by over 90%.
What comes after Wastewater treatment?
The next topic is "Sewer design", which builds directly on this one.
How difficult is Wastewater treatment?
It is classed as Advanced in Civil & Structural (topic 82 of 112). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Civil & Structural.