wtp operator training: water chemistry missouri water and wastewater conference dr. john t....
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WTP Operator Training:WTP Operator Training:
Water ChemistryWater Chemistry
Missouri Water and Wastewater Conference
Dr. John T. O’Connor, PETom O’Connor, PE
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Elements of Water ChemistryElements of Water Chemistry
• Molecular Properties of Water
• Acids and Bases - pH, pOH, Alkalinity
• Solubility Equilibria - Precipitation
• Oxidation-Reduction Reactions
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The AtomThe Atom
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Water MoleculeWater Molecule
+ +
- -
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Hydrogen Bonding - HHydrogen Bonding - H1818OO99
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HydrophobiaHydrophobia
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Ionization of HIonization of H22OO
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What are Acids & Bases?What are Acids & Bases?An Acid is a Proton (H+) Donor
A Base is a Proton (H+) Acceptor
H2O + H2O = H3O+ + OH-
[H+] = [OH-], moles/litre = 10-7 M
pH + pOH = pKw constant
7 + 7 = 14
8 + 6 = 14
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Chemical ShorthandChemical Shorthand
pH = - log [H+]pOH = - log [OH-]
pK = - log [K]
e.g., [10 -7 M] = 7
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HCl + HHCl + H22O O H H33OO++ + Cl + Cl--
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Acids and BasesAcids and BasesAcid pK Base
HCl -3 strong Cl -
H2SO4 -3 SO42-
HNO3 -1 NO3 -
H2CO3 6.3 HCO3 -
H2S 7.1 HS -
NH4 + 9.3 NH3
HCO3 - 10.3 weak CO3 2-
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Carbonate EquilibriaCarbonate EquilibriaHH22COCO33 HCOHCO33
--COCO332-2-
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AlkalinityAlkalinity
Acid Neutralizing Capacity of Water
(Ability to accept protons)
= HCO3- + 2CO3
- + OH- - H+
Titration End-Point: H2CO3 (pH≈ 4.5)
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Hydrogen SulfideHydrogen SulfideHH22S S HS HS-- S S2-2-
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Ammonium Ion Ammonium Ion AmmoniaAmmonia NHNH44
+ + NHNH33
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Precipitation & SolutionPrecipitation & Solution
Precipitation of Iron, Manganese
Formation of Coagulant Floc
Corrosion of Copper, Lead
Calcium Carbonate Stability
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Coagulation withCoagulation withFerric Hydroxide Ferric Hydroxide
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Inorganic CoagulantsInorganic Coagulants
• Aluminum Sulfate ( Filter Alum) Aluminum Sulfate ( Filter Alum)
AlAl22(SO(SO44))33 · 14H · 14H22OO Al(OH)Al(OH)3 3
• Ferric Sulfate Ferric Sulfate
FeFe22(SO(SO44))33 · 9H · 9H22OO Fe(OH)Fe(OH)33
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Metal SolubilityMetal Solubility
• OH- : Zn(OH) 2Cu(OH) 2 Cd(OH) 2
• CO32- : ZnCO3 CuCO3 CdCO3
• SS2- 2- :: ZnS ZnS CuS CdS CuS CdS
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Metal Hydroxide Solubility vs pHMetal Hydroxide Solubility vs pH
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At.Wt. Influent Effluentg/mole µg/l µg/l
Zinc 65.4 5730 690
Copper 63.5 2760 297
Cadmium 112.4 94 15
Lead 207.2 100 0
Nickel 58.7 37 13
Iron 55.8 1700 100
Metals Removal in WWTPMetals Removal in WWTP
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Oxidation-ReductionOxidation-Reduction
Oxidation is the loss of an electron
Fe2+ (ferrous ion) - e- Fe3+ (ferric ion)
Reduction is the gain of an electron
Clo (chlorine) + e- Cl- (chloride ion)
Rapid to glacially slow reaction rates
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Oxidation-ReductionOxidation-Reduction
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Oxidizing AgentsOxidizing Agents
Oxygen O°2 - 4e- O 2- (H2O)
Chlorine Cl°2 - 2e- 2Cl-
Potassium Permanganate
KMnO4 - 3e- MnO2
Hydrogen Peroxide
H2O2 - 2e- O2 + H2O
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Reducing AgentsReducing Agents
Hydrogen Sulfide H2S + 2e- S0
Nitrite Ion NO2- + 2e- NO3
-
Ferrous Ion Fe2+ + e- Fe3+
Carbon C° + 4e- CO2
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ChlorinationChlorination
Cl2 + H2S Cl - + S0
Cl2 + NO2- Cl - + NO3
-
Cl2 + 2Fe2+ 2Cl- + 2Fe3+
Rapid Reaction - Immediate Chlorine Demand
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OzonationOzonation
O3 + H2S O2 + S°
O3 + NO2- O2 + NO3
-
O3 + 2Fe2+ O2 + 2Fe3+
Rapid Reduction: O° O2- - 2e-
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The Human ElementsThe Human Elements
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Groundwater ConstituentsGroundwater ConstituentsAll water is the same.
It is only the stuff in it that is different.
• INORGANICINORGANIC
• ORGANICORGANIC
• GASGAS
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Inorganic ConstituentsInorganic Constituents
Major Ions: Ca2+, Mg2+, Na+ ; HCO3- , SO4
2-, Cl-
Nonionic: SiO2
Minor Ions: NH4+, K+ ; F-, PO4
3-
Trace Constituents:Al, As, Ba, B, Br, Cd, Cs, Cr, Co, Cu, I, Fe, Pb, Mn, Hg, Mo, Ni, Ra, Ru, Se, Ag, Sr, Sn, Ti, U, Zn
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Electroneutrality ConditionsElectroneutrality Conditions
Missouri River
Dec. 2000
Kansas City
Well Water
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Organic ConstituentsOrganic Constituents
Total Organic Carbon (TOC) =
Purgeable organic carbon (e.g., methane)+ Non-Purgeable organic carbon (NPOC)
Dissolved (natural color) (DOC)+ Particulate (bacteria, algae)
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TOC in Missouri WatersTOC in Missouri Waters
Source Water TOC (avg)
Lakes 4.8
Rivers 3.6
Wells < 100 ft. 1.2
Wells > 100 ft. 0.2
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Dissolved Gas CompositionDissolved Gas CompositionAbundance in Ground WatersAbundance in Ground Waters
Methane CH4
Nitrogen N2
Carbon dioxide CO2
Hydrogen sulfide H2S
Radon Rn
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MethaneMethane
• up to 77 mg CH4/l in Illinois Groundwaters
• early methane wells used for home heating,
cooking
• wellhouse explosions
•flaming the tap
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Physical & Inorganic Water Qualities - Constant
Cations: Hardness (calcium, magnesium), sodium, potassium, ammonium ions
Anions: Alkalinity (bicarbonate), chloride, sulfatefluoride, arsenite ions; little or no nitrate
Temperature: 12 ± 2 °Celsius; density, viscosity constant
Groundwater CharacteristicsGroundwater CharacteristicsMidwestern United StatesMidwestern United States
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GASES DO absent (converted to carbon dioxide)H2S: 0 to 1 mg/l (sulfate converted to sulfides)Methane: 0 to ~ 70 mg CH4/l
METALS Iron, manganese, lead, copper, cadmium, zinc concentrations limited by carbonate, sulfide Arsenic (AsO2
-) - commonly 0 to 50 µg /l
NITROGEN Ammonium Ion: 0 to > 5 mg N/lNitrate Ion: low (converted to nitrogen gas, N2)Nitrite Ion: low
Microbially-Mediated Microbially-Mediated Reducing Conditions Reducing Conditions in Midwestern U.S. Ground Watersin Midwestern U.S. Ground Waters
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Historical TOC DataHistorical TOC DataMissouri Finished Drinking Water SuppliesMissouri Finished Drinking Water Supplies
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Missouri Finished Drinking Water SuppliesMissouri Finished Drinking Water Supplies
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Metals in Municipal WatersMetals in Municipal WatersMissouri Finished Drinking Water SuppliesMissouri Finished Drinking Water Supplies
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Missouri Finished Drinking Water SuppliesMissouri Finished Drinking Water Supplies
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