Basic Chemical Concepts of Advanced Water Treatment CE 5345 By Douglas Rittmann, Ph.D., P.E.

Inorganic Chemistry Atomic Weight – is relative of an element to carbon-12 Atomic Weight – is relative of an element to carbon-12 Valence – is the combining power of an element relative to the hydrogen atoms Valence – is the combining power of an element relative to the hydrogen atoms Equivalent Wt of an element = Atomic Wt/Valence Equivalent Wt of an element = Atomic Wt/Valence Molecular Wt- Sum of atomic weights expressed in grams Molecular Wt- Sum of atomic weights expressed in grams

Inorganic Chemistry Equivalent Wt. – M.W./moles of Hydrogen Equivalent Wt. – M.W./moles of Hydrogen Example: H 2 SO 4 = 98/2 = 49 g; Example: H 2 SO 4 = 98/2 = 49 g; Example: HCl = 36.5/1 = 36.5 g Example: HCl = 36.5/1 = 36.5 g Radicals – special group of molecules that are not compounds but are part of compounds. Radicals – special group of molecules that are not compounds but are part of compounds. Examples are: OH - = hydroxyl, HCO - 3 = bicarbonates, CO - 3 = Carbonates, PO -3 4 = orthphosphate, SO -2 4 = Sulfates, NO - 3 = Nitrates, OCl - = hypochlorite Examples are: OH - = hydroxyl, HCO - 3 = bicarbonates, CO - 3 = Carbonates, PO -3 4 = orthphosphate, SO -2 4 = Sulfates, NO - 3 = Nitrates, OCl - = hypochlorite

Concentration Units Mg/L = PPM when Specific Gravity = 1.0 Mg/L = PPM when Specific Gravity = 1.0 Concentration of Elements expressed as mg/L Concentration of Elements expressed as mg/L Example: Na in water = 36.2 mg/L Example: Na in water = 36.2 mg/L Hardness expressed as a compound = mg/L as CaCO 3 or as Ca +2 as Ca +2 & Mg +2 as Mg +2 Hardness expressed as a compound = mg/L as CaCO 3 or as Ca +2 as Ca +2 & Mg +2 as Mg +2 Alkalinity expressed either as compound = mg/L as CaCO 3 or as radical such as HCO - 3, Alkalinity expressed either as compound = mg/L as CaCO 3 or as radical such as HCO - 3, CO -2 3, OH - Milli-equivalents/liter (meq/l)= mg/L/meq wt. expresses equivalent wt as milligrams. Milli-equivalents/liter (meq/l)= mg/L/meq wt. expresses equivalent wt as milligrams.

Hydrogen Ion Concentration Pure Water = H 2 O ↔ H + + OH - Pure Water = H 2 O ↔ H + + OH - pH = log 1/[H + ], pH scale = 0 to 14, 7.0 = alkaline, 7.0 = neutral pH = log 1/[H + ], pH scale = 0 to 14, 7.0 = alkaline, 7.0 = neutral

Chemical Equilibria Chemical reactions are reversible Chemical reactions are reversible aA + bB ↔ cC + dD where A,B = reactants and C,D = products An increase in A or B shifts the reaction to the right and an increase in C or D shifts it to the left. Mass Action equation = [C] c [D] d /[A] a [B] b = K where [ ] = molar concentration K = equilibrium constant

Chemical Equilibria K sp is termed the solubility product constant K sp is termed the solubility product constant Example: [Ca +2 ][CO 3 -2 ]=K s K=K sp =5X10 -9 at 25 o C Example: [Ca +2 ][CO 3 -2 ]=K s K=K sp =5X10 -9 at 25 o C Mg/L = (5X10 -9 ) 1/2 X 100/1000 = 7.07, where 100 = MW of CaCO 3, 1000 mg = 1 gram 100 = MW of CaCO 3, 1000 mg = 1 gram

Ways to Shift Equilibria Example of insoluble CaCO 3 in water softening: Ca HCO Ca(OH) 2 ↔ 2CaCO 3 ↓ + 2CO 2 Ca HCO Ca(OH) 2 ↔ 2CaCO 3 ↓ + 2CO 2 Example of poorly ionized constant of water: [H + ] + [OH - ] = K w = [H + ] + [OH - ] = K w =

pH and Alkalinity Alkalinity is the capacity of water to neutralize acids. Alkalinity is the capacity of water to neutralize acids. Three chemical forms of alkalinity: HCO 3 -, CO 3 -, OH - Three chemical forms of alkalinity: HCO 3 -, CO 3 -, OH - Buffers are substances that resist pH change such as bicarbonate-carbonate system. Buffers are substances that resist pH change such as bicarbonate-carbonate system.

Physical Chemistry Zero-Order Reactions occur at a rate that is independent of the concentration of the reactant or product. C = C o - kt, plot straight line on arithmetic graph paper, slope = k Zero-Order Reactions occur at a rate that is independent of the concentration of the reactant or product. C = C o - kt, plot straight line on arithmetic graph paper, slope = k First-Order Reactions occur at a rate that is proportional to the concentration of one reactant. C/C o =e -kt, plots straight line on Log paper, k = slope First-Order Reactions occur at a rate that is proportional to the concentration of one reactant. C/C o =e -kt, plots straight line on Log paper, k = slope Second-Order proceed at a rate proportional to the second power. – dC/dt = kC 2 = -r, r = rate of change in concentration of A with time, mg/l-day, k = rate constant, l/mg-day, C = concentration of A at any time, mg/L, Plots straight line on arithmetic paper. Second-Order proceed at a rate proportional to the second power. – dC/dt = kC 2 = -r, r = rate of change in concentration of A with time, mg/l-day, k = rate constant, l/mg-day, C = concentration of A at any time, mg/L, Plots straight line on arithmetic paper.

Gas Laws General Gas Law = P 1 V 1 /T 1 = P 2 V 2 /T 2, where P1,P2= absolute gas pressures; V 1,V 2 = gas volumes; T 1,T 2 = absolute Temp., o R, o K General Gas Law = P 1 V 1 /T 1 = P 2 V 2 /T 2, where P1,P2= absolute gas pressures; V 1,V 2 = gas volumes; T 1,T 2 = absolute Temp., o R, o K Dalton’s law = mixture of gases exert a pressure independent of the others. Dalton’s law = mixture of gases exert a pressure independent of the others. Henry’s Law = weight of gas will dissolve in a liquid volume at a constant temperature proportional to the pressure the gas exerts above the liquid. Henry’s Law = weight of gas will dissolve in a liquid volume at a constant temperature proportional to the pressure the gas exerts above the liquid.

Colloidal Dispersions Colloids are ultrafine dispersions or suspensions, surface area to mass ratio is very high. Colloids are ultrafine dispersions or suspensions, surface area to mass ratio is very high. Colloids may be positive or negatively charged Colloids may be positive or negatively charged Colloids reflect light and measured by turbidity meter. Colloids reflect light and measured by turbidity meter. Colloids have great adsorptive powers Colloids have great adsorptive powers Colloids are removed by reverse osmosis Colloids are removed by reverse osmosis

Priority Pollutants Are selected on the basis of their acute toxicity Are selected on the basis of their acute toxicity Toxic Inorganic Chemicals are heavy metals such as barium, Cd, Pb, Hg, & non-metals As, & Se Toxic Inorganic Chemicals are heavy metals such as barium, Cd, Pb, Hg, & non-metals As, & Se Toxic Organic chemicals are endrin, benzene, carbon tetrachloride, 1,2-dichloroethane, 1,1,1- trichloroethane,1,1-dichloroethylene, trichloroethylene, and vinyl chloride are SOCs classified as VOCs. Toxic Organic chemicals are endrin, benzene, carbon tetrachloride, 1,2-dichloroethane, 1,1,1- trichloroethane,1,1-dichloroethylene, trichloroethylene, and vinyl chloride are SOCs classified as VOCs.