C10: Waste Water Treatment Flashcards
Where does waste water come from?
At home - baths, toilets, washing-up etc.
Agricultural systems - nutrient run-off, slurry
Industrial processes
Why must sewage from domestic or agricultural sources be treated?
To remove any organic matter and harmful microbes - otherwise pollution and poses health risks
Why must industrial waste be treated?
Can also contain harmful chemicals - so must undergo additional stages of treatment before it’s safe
What’s the first stage of sewage treatment?
Screened: removing large bits of material (twigs, plastic bags) as well as any grit
What’s the second sage of sewage treatment?
Stands in a settlement tank & undergoes sedimentation: the heavier suspended solids sink to bottom to produce sludge, while the lighter effluent floats at the top
What’s the third step of sewage treatment?
Effluent in settlement tank is removed and treated by biological aerobic digestion - when air is linked through the water to encourage bacteria to break down any organic matter in the water (including other microbes)
What’s the fourth stage of sewage treatment?
The sludge is also removed and transferred into large tanks. Here it gets broken down by bacteria in a process of anaerobic digestion.
What’s the fifth stage of sewage treatment?
Anaerobic digestion breaks down the organic matter in the sludge, releasing methane gas m. The methane can be used as an energy source and the remaining digested waste can be used as a fertilised
What’s the sixth stage of sewage treatment?
For waste water containing toxic substances, additional stages of treatment may invoice adding chemicals (eg. to precipitate metals), UV radiations or using membranes
Compare the treatment of sewage to the treatment of fresh water.
Sewage treatment require more processed but uses less energy than the desalination of salt water, so could be used in areas without much fresh water. But people don’t like the idea of drinking water that used to be sewage.
