Calcium Carbonate Saturation

1. Calcium Carbonate Saturation WQT 134 Aquatic Chemistry II Standard Methods 20th ed #2330 Calcium Carbonate Saturation

2. Week 5 Objectives Reading assignment: American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation (WEF). 1999.  Standard Methods for the Examination of Water and Wastewater, 20th edition • Understand the function of the marble test 2. Understand the role of calcium carbonate saturation in corrosiveness. 3. Understand how to measure calcium carbonate saturation (SM #2330)

3. Calcium Carbonate Saturation WQT 134 Environmental Chemistry II STM. 20th edition. #2330

4. Calcium Carbonate “Marble Test” Experimental Design Part 1 Standardization of Titrant (Sulfuric acid)=purchased from Hach! Part 2 Titration for Total Alkalinity determine p alkalinity determine T Alkalinity mg/L as CaCO3/L Part 2 ADD 0.5 g CaCO3 + redue! pH above 8.3 = P alkalinity color change 0.02 N Sulfuric acid P alkalinity 200 ml of sample + 5 drops Phenolphthaleinindicator no color change Palkalinity =0 or titrate to pH 8.3 Blue Color change after addition of Bromcresol green/methyl red pH 4.5 = T alkalinity red color change endpoint T alkalinity + 5 drops Mixed bromcresol green-methyl red titrate to pH 4.5 pH Met4er stir bar stir plate

5. Calcium Carbonate Saturation #2330 • What is Calcium carbonate saturation? • The sample pH and total alkalinity are determined. Then the sample is saturated with calcium carbonate and the procedure is repeated. A comparison of the before and after values is done by subtraction to determine if the system is under saturated, saturated, or in equilibrium with calcium carbonate. • Why do we care? • This test helps to determine how much lime or soda ash are needed to keep a distribution system in good operating condition

6. Calcium Carbonate Saturation #2330 • Why is it important in wastewater industry? • the corrosiveness of the water leaving the plant. • Why is it important in water industry? • Aesthetic taste of water and to prevent corrosiveness of lines.

7. Calcium Carbonate Saturation #2330 • What are some assumptions in procedure? • View procedure as a qualitative guide to the behavior of CaCO3 in aqueous systems

8. Calcium Carbonate Saturation #2330 • What are some interferences in procedure? • Deposition from oversaturated waters is inhibited by the presence of phosphates (particularly polyphosphates), certain naturally occurring organics, and magnesium

9. Calcium Carbonate Saturation #2330 Calculations and Formulas? Step 1 Calculate pH(1) of original sample Step 2 Calculate alkalinity alk (1) of original sample Alk(1) T Alkalinity mg/L as CaCO3/L= (ml of acid to 8.3=colorless+ ml to reach pH 4.5=pink)(Normality)(50mg/meq CaCO3)(1000 ml) ml of original sample volume Step 3 Calculate pH(2) of 0.5 g spiked CaCO3 sample Step 4 Calculate alk(2) of 0.5 gspiked CaCO3 sample (ml of acid to 8.3=colorless+ ml to reach pH 4.5=pink)(Normality)(50mg/meq CaCO3)(1000 ml) ml of original sample volume

10. Calcium Carbonate Saturation Calculations and Formulas? Step 5 A= samples prior to saturation B= samples after saturation Eq 1: A-B= Stability Index Eq 2: Alk(1)-Alk(2)= +, -, 0 Eq 3: pH(1) – pH(2)= +, -, 0 A>B- water is supersaturated with respect to carbonate and may forma precipitate scale A<B water is undersaturated with respect to carbonate and may be corrosive A=B water is in equilibrium with respect to carbonate constituents

11. Calcium Carbonate Saturation #2330 • Tips and Suggestions? • Use ample sample volume (300 ml); its trial and error • Leave the lime behind • Add H2SO4 slowly! • Keep track of H2SO4added each time! • Rely solely on indicators or can use pH probe!