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pollutants in waste water

heavy metals (mining and industrial processes), pesticides (farming), dioxins (waste incineration w/Cl), polychlorinated bipheryls (PCBs) (capacitors, transformers), organic matter (farming), nitrates (intensive animal farming, fertilizers), phosphates (detergents)

primary treatment

filtration, sedimentation, flocculation, skimming

primary treatment: filtration

removes large objects

primary treatment: sedimentation

removes sand and small objects

primary treatment: flocculation

removes suspended solids during precipiation (Al2(SO4)3 + 3Ca(OH)2 --> 2Al(O)3 (s) + 3CaSO4

primary treatment: skimming

removes grease from surface

secondary treatment

activated sludge process (removes most of O2-demanding wastes): 1. sewage treated w/O2 in sedimentation tank; 2.sludge containing bacteria, microbes settles out; 3. discharged water is disinfected w/chlorine or ozone

tertiary treatment

removal of heavy metals, removal of phosphates, removal of remaining organic matter, removal of nitrates

removal of heavy metals

precipitation with hydroxides or carbonates (Pb(2+) + 2OH(-) --> Pb(OH)2)

removal of phosphates

w/CaO or Al(SO4)3 --> Al(3+) + PO4(3-) --> AlPO4

removal of remaining organic matter

activated carbon beds, oxidize absorbed organic matter when heated to CO2 and H2O

removal of nitrates

ion exchange: passed through resins with silicates/zealites, Na(+) replaced by H(+), Cl(-) by OH(-) (H(+) + OH(-) -->H2O), requires no heating or fuel, but resins need to be replaced/regenerated

obtaining freshwater

multistage distillation, reverse osmosis

multistage distillation

1. seawater heated; 2. in another container, pressure is lowered and seawater boils rapidly; 3. remaining seawater sent through additional stages, each w/ lower pressure

reverse osmosis

1. semipermeable membrane; 2.seawater subjected to high pressure; 3. water passes through membrane

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