15 terms

IB Environmental Chemistry: Water Treatment

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