Chapter 5 (CIC) and Chapter 18 (CTCS) Read in CTCS Chapter Problems in CTCS: 18.33, 35, 37

SDWA – 1974 and 1996 Protects public water supplies Maximum Contaminant Level Goal (MCLG) –154 lb (70 kg) person drinking 2 L for 70 yrs with no ill effects Maximum Contaminant Level (MCL) –Legal limit –83 regulated contaminants Clean Water Act – 1972 protects surface waters

MCLG’s and MCL’s for Selected Pollutants in Drinking Water PollutantMCLG (ppm) MCL (ppm) Cadmium (Cd 2+ )0.005 Chromium (Cr 3+, CrO 4 2- )0.1 Lead (Pb 2+ ) Mercury (Hg 2+ )0.002 Nitrate (NO 3 - )10 Benzene (C 6 H 6 ) Trihalomethanes (CHCl 3, etc.) * All carcinogens MCLG is 0 – Delaney Clause

Water Treatment Coarse filtration – screen Alum and slaked lime in settling tank Al 2 (SO 4 ) 3 + Ca(OH) 2  Al(OH) 3 (s) + CaSO 4 (aq) Gravel and sand filtration Aeration Chlorination (Cl 2, NaOCl, or Ca(OCl) 2  HOCl – to 0.6 ppm) –Can form THM’s

O 3 is –More expensive –More effective –Can’t protect water once it leaves facility so chlorination is still necessary UV is –Fast –Economical –Chlorination must still be done Fluoridation is done by adding 1ppm F - (NaF)

Hard Water Ions of Ca 2+, Mg 2+, and Fe 3+ with counterions of Cl -, HCO 3 -, and SO 4 2- varying up to 400 ppm Doesn’t differentiate Mg 2+ or Fe 3+ from Ca 2+ Do EDTA titration to measure Wrecks water heaters, pipes and forms soap scum by precipitating with with soap

Removal of Hard Ions Ion Exchange Beads filled with Na + Beads have greater attraction for Ca 2+ and Mg 2+ As you use water, the system exchanges sodium (soft cations) for hard ions At night, the beads are bombarded with very concentrated NaCl, washing away the hard ions into the drain

Pb 2+ Heavy metals in their elemental form are insoluble Pb pipes used since ancient times Homes older than 1930 have Pb pipes –Replaced with Cu or PVC More acidic water will react with metal to form the ion M + 2H +  M 2+ + H 2 Hard water deposits can block this to some extent Pb 2+ accumulates in brain and bones

Other Contaminants THM’s - HOCl + humic acids Hg – another insoluble metal (CH 3 Hg + ) Pesticide residues – DDT PCB’s – used in electrical transformers Dioxins – byproduct of paper manufacturing TCE – drycleaning Phosphates – detergents (uncontrolled algae growth) NO manure and fertilizer

Tap Water Very safe due to SDWA Is it pure? Na +, Ca 2+, Mg 2+, Fe 3+, Cl -, HCO 3 -, and SO 4 2- Biggest problems are – Hard water –Pb 2+ –THM’s

Bottled Water Regulated by FDA not SDWA Comes from springs and wells Can disinfect with O 3 and UV so it should be healthier than tap water Is it pure? Depends –Large Ca 2+, dissolved CO 2, and sometimes H 2 S

Filtered Water Activated Carbon absorbs nonionics like Cl 2, THM’s, pesticide residues, and solvents Ion exchange resin removes –Pb 2+, Cu 2+, Ca 2+, Mg 2+ It is 20% the cost of bottled water

International Waters Ocean is 3.5% NaCl and white cells are 0.9% NaCl –Osmosis will suck water out of your cells to dilute the concentrated salt water that you drink Desalination –Distillation – lots of energy due to the high specific heat of water (H-bonds) –Reverse osmosis – requires high pressures (energy)