Chemistry: sewage treatment

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8 Terms

1
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need of sewage treatment

needed to control disease, most dangerous microorganisms are waterborne

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levels of sewage treatment

  1. primary

  2. secondary

  3. tiertery

3
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levels of sewage treatment: primary

  1. screening removes large objects

  2. sedimentation lets soilds settle

  3. composting of solid kills pathogen bacteria making it safe

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levels of sewage treatment: secondary

  1. all of primary treatment

  2. biological oxidation induces growth of aerobic microorganisms which digest the sewage killing teh bacteria

  3. sedimintation, solids settle and liquid is discharged into rivers, liquid is safe and sutritous

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problems with secondary treatment

eutrophication, phosphates and nitrates in the treated sewage causes excess plant growth killing fish

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levels of sewage treatment: tertiery

  1. all of secondary treatment

  2. removes nitrates and phospates ions by percipitation

  3. prevents eutrophication

  4. expensive

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causes of eutrophication

sewage treatment

silage effluent

pig slurry

fertilisers washing of farm

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5 day BOD (biochemical oxygen demand)

measure of organic pollution in water

test sample immediately after wrinkler method and rcord oxygen content

may need to dilute with fully oxygenated water if oxygen content is too little

leave second sample in teh dark at 20 degrees C for 5 days