1. Sewage Treatment Introduction Needed to control disease
Various degrees of treatment
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2. No Treatment Straight into rivers Your problem is washed downstream.
You get it from upstream
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3. Primary Treatment (i) Screening – removing lumpy bits
(ii) Sedimentation – allow solids to settle
Discharge of liquid –
Composting of solids left behind kills pathogenic bacteria
Better than nothing but not great
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4. Secondary Treatment
Follows primary
Much better
(i) Biological Oxidation [E.g. Activated Sludge Process]
stir the sludge vigorously [or pour over large surface area to oxygenate]
encourages growth of aerobic micro-organisms
these digest the sewage and destroy pathogens
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5. liquid is then discharged into rivers etc.
(ii) Sedimentation
liquid is then discharged into rivers etc.
Biologically safe i.e. you wont get disease from it
problem Eutrophication
Excess plant growth caused by excess nutrients.
When these run out the plants die, rot and use up the oxygen which kills almost all the animals and Destroys the habitat.
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6. Tertiary Treatment Follows Secondary Treatment
Not common because it is expensive
Removes ions by precipitation
PO43- [phosphate] and NO31- [nitrate]
These ions cause eutrophication – ecess plant growth caused by excess nutrients
Water completely now safe.
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7. Test
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8. List the different ways in which sewage is treated and briefly explain what happens in each.[15] Primary / screening / sedimentation / discharge liquid / composting of solids // secondary / biological oxidation / active sludge / aerobic micro-organisms / digest sewage / kill pathogenic / sedimentation / discharge liquid / biologically safe // tertiary / removal of PO4 / and NO3 ions / by precipitation / discharge / totally safe
2. What is eutrophication and what problems does it cause? [8] Excess plant growth / caused by excess nutrients / when these run out / plants die / rot / use up oxygen / produce toxins / kill most life in pond /
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