1. Sulfates Presentation By Douglas Rittmann, Ph.D., P.E. Water/Wastewater Consultant To CE 4153 Lab Course On February 7, 2006

2. General Considerations 1. Cathartic effect on humans in excessive amounts 2. U.S. Public Health recommends maximum limit of 250 mg/L 3. Forms Hard scales in boilers and heat exchangers 4. Causes odors in sewers and hot water heaters 5. Causes sewer-corrosion problems in sewers 6. Hydrogen sulfide is formed under anaerobic conditions

3. Methods of Analysis Gravimetric Method 1. Considered the most accurate method above 10 mg/L as Sulfate 2. Barium ion combines with sulfate ion to form barium sulfate. 3.Digestion at near boiling temperature forms crystals in order to make it filtrable with gooch crucible and asbestos mat. 4. Washing removes excess barium and other salts. 5. Major limitation is the time required.

4. Method of Analysis Turbidimetric Principle: Barium sulfate is precipitated with acetic acid with barium chloride. Light absorbance measures the barium sulfate Suspension by a photometer which is compared to sulfate standard curve. Interference: Color or suspended solids. S.S. can be removed by filtration. Silica >500 mg/L will interfere also. Minimum Detection concentration: 1 mg/L Apparatus: 1. Nephelometer or Spectrophotometer or Filter photometer 2. Magnetic stirrer 3. Stopwatch or timer 4. spoon

5. Method of Analysis Turbidimetric Reagents: 1. Dissolve 30 g magnesium chloride, 5 g sodium acetate, 1.0 g Potassium nitrate, and 20 ml of acetic acid in 500 ml distilled water and dilute to 1000 ml. 2.Barium crystals, 20-30 mesh. 3.Prepare standard: Sulfate solution by dissolving 0.1479 g of anhydrous sodium sulfate diluted to 1000 ml. Standard solution: 1 ml = 100 µg of Sulfate

6. Method of Analysis Procedure a.Formation of barium sulfate turbidity: Measure 100 ml sample into 250 ml erlenmeyer flask. Add 20 ml buffer solution and mix. While mixing add spoonful of barium chloride crystals and begin timing. Stir for 60 seconds at constant speed. b. After mixing period, measure turbidity in photometer after 5 minutes. c.Estimate sulfate level compared to standard sulfate curve. Space standards at 5 mg/L intervals from 0 to 40 mg/L sulfate range. d.Correction for Color and turbidity: Correct for color and turbidity by running blanks without barium chloride.

7. Method of Analysis Calculation Mg/L Sulfate = mg sulfate X 1000/ml sample Precision and Bias With a turbidimeter in a single laboratory with a sample having a mean of 7.45 mg sulfate per liter, a standard deviation of 0.13 mg/L and a coefficient of variation of 1.7% were obtained. Two samples with sulfate gave recoveries of 85 and 91 per cent.

8. Applications of Sulfate Data 1. Drinking water compliance of sulfates at <250 mg/L MCL 2. Sulfate in wastewater determines magnitude of sulfide problems 3. Sulfate under anaerobic digestion forms sulfide. 4. Anaerobic digestion forms methane, carbon dioxide and sulfide. 5. Hydrogen sulfide gas content should be <50 grains/100 cu.ft. 6. Gas scrubbing necessary if hydrogen sulfide >50 grains/100 cu.ft.

9. Questions?