ENVR 403 Introduction to Environmental Chemistry Philip C. Singer Department of Environmental Sciences and Engineering phil_singer@unc.edu 919-966-3865 April 2010

1. Chemistry of Natural Waters 2. Purification of Water Topics 1. Chemistry of Natural Waters 2. Purification of Water

1. Chemistry of Natural Waters Redox Equilibria -speciation -dissolved oxygen resources Acid-Base Equilibria -the carbonate system and alkalinity Solubility Equilibria -metal solubility -aqueous lead (Pb) solubility

pH and pE as Master Variables H2CO3 = HCO3- + H+ Ka1 pH = pKa1 + Log [HCO3-]/[H2CO3] NO3- + 10H+ + 8e- = NH4+ + 3H2O Kred pE = -1/8 (pKred) + 1/8 (Log [NO3-] [H+]10/[NH4+]) pEo = -1/n (Log Kred) pE = pEo + 1/n Log [Ox]/[Red]) Analogous to Nernst Equation EH = EoH + 2.3 RT/nF (Log [Ox]/[Red])

After M. Benjamin, 2002

After M. Benjamin, 2002

After M. Benjamin, 2002

After M. Benjamin, 2002

Electroneutrality Equation (Charge Balance) for Natural waters Major Cations: Na+, K+, Ca2+, Mg2+ Major Anions: Cl-, SO42- , NO3-, HCO3-, CO32- Charge Balance [Na+] + [K +] + 2[Ca2+] + 2[Mg2+] + [H +] = [Cl- ]+ 2[SO42-] + [NO3-] + [HCO3-] + 2[CO32-] + [OH-] Cb-Ca = Acid neutralizing Capacity = Alkalinity = [HCO3-] + 2[CO32-] + [OH-] – [H +]

What is the pH of pure rainwater? Pure rainwater contains only dissolved CO2 in equilibrium with the atmosphere. H2CO3 = KH PCO2 ~ 10-5M What is the pH of a 10-5M solution of H2CO3? Cb-Ca = Alkalinity = 0 [H+] = [HCO3-] + 2[CO32-] + [OH-] = K1[H+]C/D + 2 K1K2C/D where D = [H+] 2 + K1 [H+] + K1K2 Answer: pH 5.65

If a body of water has a pH of 7 If a body of water has a pH of 7.5 and an alkalinity of 2x10-3 equivalents/L, what is the equilibrium pH of the water if 10-3 eq./L of acid is added to the water? Use initial pH and given alkalinity to find total carbonate concentration C C = (Alkalinity + [H+] - [OH-]) /((K1[H+]/D) + 2K1K2/D) = 2.12x10-3 M Added acid consumes alkalinity New alkalinity = 2x10-3 – 10-3 = 10-3 eq/L Find new pH from alkalinity expression Alkalinity = [HCO3-] + 2[CO32-] + [OH-] – [H +] 10-3 = ((K1[H+]/D) + 2K1K2/D) 2.12 x10-3 + [OH-] – [H +] Find pH = 6.35

After M. Benjamin, 2002

Solubility of CaCO3(s) Kso = [Ca2+][CO32-] [Ca2+] = Kso/[CO32-] = Kso/α2[TOTCO3] Solubility of Ca increases with decreasing pH

Lead in Drinking Water CO3 2-, PO43- OCl- Cl- Pb 2+ Pb(IV)O2, Pb3(CO3)2OH2, PbCO3, Pb5(PO4)3OH Lead Pipe Pb(0) CO3 2-, PO43-, Cl- Pb2+ Particulate Pb(II) Pb(IV) Note why we are studying orthophosphate, DIC, chloramines, and pH. Decrease in oxidizing potential will lead to dissolving of PbO2 with low alk and pH Increase alkalinity (DIC) and pH to ppt lead carbonates. Add orthophosphate to ppt lead phosphates. Lead pipe (Pb0) develops scales of corrosion products. The products formed (oxides, carbonates, and phosphates) depend on the water chemistry. Changes in distribution system water chemistry can destabilize corrosion products. Optimization of water chemistry can mitigate lead release to solution. 28

Solubility of Potential Lead-containing Phases Plattnerite (PbO2) -2 Hydrocerussite (Pb3(CO3)2(OH)2) with 50 mg/L DIC -3 Litharge (PbO) -4 Hydroxylpyromorphite (Pb5(PO4)3OH) with 1 mg/L P (M) diss -5 -6 Log[Pb] 15 ug/L Pb -7 -8 -9 4 5 6 7 8 9 10 11 pH

Conventional and Waterfree Urinal

Operation of Falcon Waterfree cartridge Urine in Source: Falcon Waterfree

Fed Ex Global Health Building (high use) Falcon—6 months Fed Ex Global Health Building (high use)

Chemical Composition of Urine (Udert et al. 2003)

Underlying Chemical Theory: Hydrolysis of Urea NH2(CO)NH2+2H2O2NH4++CO3-2 Urease is urea-hydrolyzing enzyme Urease decomposes urea into ammonium and carbonate, causing the pH to increase Increase in pH and addition of ammonium and carbonate leads to over-saturation with respect to several different minerals, including struvite (MgNH4PO4) and calcium hydroxyapatite Ca5(PO4)3(OH)2.

Comparison of XRD patterns with struvite reference pattern.

O P Mg Ca SEM Results for RDU Terminal A Composition Similar to Struvite, MgNH4PO4 (s)