AWPPCE HW 9
Problem 1
From diagram you can see that
Total hardness = 200 mg/L as CaCO3
Ca hardness = 100 mg/L as CaCO3
Mg hardness = 100 mg/L as CaCO3
Total alkalinity = bicarbonate alkalinity = 50 mg/L as CaCO3
So
carbonate hardness = 50 mg/L as CaCO3
non-carb. hardness = 150 mg/L as CaCO3
The purpose is to help see the chemical composition. Increasing Ca hardness alkalinity and pH increase
scaling and decrease corrosion. Increasing temp increases scaling and corrosion. This aids in deciding
how much lime or soda ash to add to soften the water. Other methods are ion exchange, zeolite, or
other chemical processes.
Problem 2
There are many common methods for cyanide removal from water:
Chlorination: HCl will break the bonds in HCN. Add chlorine gas and sodium dioxide to water
Iron Salts: Ferrocyancide is less toxic because it does not release as much cyanide into solution. Ferrous
sulfates with cyanide can be oxidized to ferrous complexes which may still be toxic but precipitate and
can be removed in sedimentation
Ozone: Using an ozone generator to dissolve ozone into water stream. Ozone will not combine with
organics to create any toxic compounds.
Increasing temperature of water stream will induce detoxification
Also EPA recommends granular activated carbon in combination with packed tower aeration/ mixing the
air in will absorb CO2 into the water and formation of carbonic acid will break the HCN bond creating
HOCN
Problem 3
Cr(VI) is a result of metal working a plating. Being a toxic pollutant that is easily transported through
water, it deserves a great deal of attention.
Remediation methods include:
Chemical reduction- direct introduction of a reducing chemical agent like zero valent iron or sulfite to
reduce to Cr(III)
Chemical precipitation- atomized slag and liquid hydroxyapatite
Bioreduction- yeast, bacteria, fungi and algae for anaerobic and aerobic reduction