WTP Operator Training: Water Chemistry Missouri Water and Wastewater Conference Dr. John T. O’Connor, PE Tom O’Connor, PE

Elements of Water Chemistry Molecular Properties of Water Acids and Bases - pH, pOH, Alkalinity Solubility Equilibria - Precipitation Oxidation-Reduction Reactions

The Atom

Water Molecule ++ -

Hydrogen Bonding - H 18 O 9

Hydrophobia

Ionization of H 2 O

What are Acids & Bases? An Acid is a Proton (H + ) Donor A Base is a Proton (H + ) Acceptor H 2 O + H 2 O = H 3 O + + OH - [H + ] = [OH - ], moles/litre = M pH + pOH = pKw constant 7+7=14 8+6=14

Chemical Shorthand pH = - log [H + ] pOH = - log [OH - ] pK = - log [K] e.g., [10 -7 M] = 7

HCl + H 2 O  H 3 O + + Cl -

Acids and Bases AcidpK Base HCl-3 strong Cl - H 2 SO 4 -3SO 4 2- HNO 3 -1NO 3 - H 2 CO 3 6.3HCO 3 - H 2 S 7.1HS - NH NH 3 HCO weak CO 3 2-

Carbonate Equilibria H 2 CO 3  HCO 3 -  CO 3 2-

Alkalinity Acid Neutralizing Capacity of Water (Ability to accept protons) = HCO CO OH - - H + Titration End-Point: H 2 CO 3 (pH≈ 4.5)

Hydrogen Sulfide H 2 S  HS -  S 2-

Ammonium Ion  Ammonia NH 4 +  NH 3 NH 4 +  NH 3

Precipitation & Solution Precipitation of Iron, Manganese Formation of Coagulant Floc Corrosion of Copper, Lead Calcium Carbonate Stability

Coagulation with Ferric Hydroxide

Inorganic Coagulants Aluminum Sulfate ( Filter Alum)Aluminum Sulfate ( Filter Alum) Al 2 (SO 4 ) 3 · 14H 2 OAl(OH) 3 Ferric SulfateFerric Sulfate Fe 2 (SO 4 ) 3 · 9H 2 OFe(OH) 3

Metal Solubility OH - : Zn(OH) 2  Cu(OH) 2 Cd(OH) 2 CO 3 2- : ZnCO 3 CuCO 3 CdCO 3 S 2- : ZnS CuS CdSS 2- : ZnS CuS CdS

Solubility Products, K sp [Cu 2+ ] [OH - ] 2 = [Zn 2+ ] [OH - ] 2 = [Ni 2+ ] [OH - ] 2 = [Cd 2+ ] [OH - ] 2 =

Metal Hydroxide Solubility vs pH

Solubility Products, K sp [Cd 2+ ] [CO 3 2- ]= [Zn 2+ ] [CO 3 2- ]= [Cu 2+ ] [S 2- ]= [Cd 2+ ] [S 2- ]= [Zn 2+ ] [S 2- ]=

At.Wt. Influent Effluent g/mole µg/l µg/l Zinc Copper Cadmium Lead Nickel Iron Metals Removal in WWTP

Oxidation-Reduction Oxidation is the loss of an electron Fe 2 + (ferrous ion) - e -  Fe 3 + (ferric ion) Reduction is the gain of an electron Cl o (chlorine) + e -  Cl - (chloride ion) Rapid to glacially slow reaction rates

Oxidation-Reduction

Oxidizing Agents Oxygen O° 2 - 4e -  O 2- (H 2 O) Chlorine Cl° 2 - 2e -  2Cl - Potassium Permanganate KMnO 4 - 3e -  MnO 2 Hydrogen Peroxide H 2 O 2 - 2e -  O 2 + H 2 O

Reducing Agents Hydrogen Sulfide H 2 S + 2e -  S 0 Nitrite Ion NO e -  NO 3 - Ferrous IonFe 2+ + e -  Fe 3+ CarbonC°+ 4e -  CO 2

Chlorination  Cl 2 + H 2 S  Cl - + S 0  Cl 2 +NO 2 -  Cl - + NO 3 - Cl 2 +2Fe 2+  2Cl - + 2Fe 3+ Rapid Reaction - Immediate Chlorine Demand

Ozonation  O 3 + H 2 S  O 2 + S °  O 3 +NO 2 -  O 2 + NO 3 - O 3 +2Fe 2+  O 2 + 2Fe 3+ Rapid Reduction: O°  O e -

Organic (Carbon) Molecules

The Human Elements

Hydrogen Isotopes

Hydrogen, Carbon Isotopes

Groundwater Constituents All water is the same. It is only the stuff in it that is different. INORGANIC ORGANIC GAS

Inorganic Constituents Major Ions: Ca 2+, Mg 2+, Na + ; HCO 3 -, SO 4 2-, Cl - Nonionic: SiO 2 Minor Ions: NH 4 +, K + ; F -, PO 4 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

Electroneutrality Conditions Missouri River Dec Kansas City Well Water

Organic Constituents Total Organic Carbon (TOC) = Purgeable organic carbon (e.g., methane) + Non-Purgeable organic carbon (NPOC) Dissolved (natural color) (DOC) + Particulate (bacteria, algae)

TOC in Missouri Waters Source Water TOC (avg) Lakes4.8 Rivers3.6 Wells < 100 ft.1.2 Wells > 100 ft.0.2

Dissolved Gas Composition Abundance in Ground Waters MethaneCH 4 Nitrogen N 2 Carbon dioxideCO 2 Hydrogen sulfideH 2 S Radon Rn

Methane up to 77 mg CH 4 /l in Illinois Groundwaters early methane wells used for home heating, cooking wellhouse explosions flaming the tap

Physical & Inorganic Water Qualities - Constant Cations:Hardness (calcium, magnesium), sodium, potassium, ammonium ions Anions:Alkalinity (bicarbonate), chloride, sulfate fluoride, arsenite ions; little or no nitrate Temperature:12 ± 2 °Celsius; density, viscosity constant Groundwater Characteristics Midwestern United States

GASESDO absent (converted to carbon dioxide) H 2 S: 0 to 1 mg/l (sulfate converted to sulfides) Methane: 0 to ~ 70 mg CH 4 /l METALSIron, manganese, lead, copper, cadmium, zinc concentrations limited by carbonate, sulfide Arsenic (AsO 2 - ) - commonly 0 to 50 µg /l NITROGENAmmonium Ion: 0 to > 5 mg N/l Nitrate Ion: low (converted to nitrogen gas, N 2 ) Nitrite Ion: low Microbially-Mediated Reducing Conditions in Midwestern U.S. Ground Waters

Missouri Surface Water Supplies Surface (stream and lake waters) vary seasonally in temperature, algal blooms; runoff from farmland and feedlots.

Historical TOC Data Missouri Finished Drinking Water Supplies

Missouri Finished Drinking Water Supplies

Metals in Municipal Waters Missouri Finished Drinking Water Supplies

Hardness + Sodium Missouri Finished Drinking Water Supplies Hardness + Sodium Missouri Finished Drinking Water Supplies

Missouri Finished Drinking Water Supplies

Hardness - MO Surface Waters