1. Harry D. Gong, Jr., P.E. Engineering Coordinator Drinking Water Revolving Loan Fund Bureau of Public Water Supply Mississippi State Department of Health

2. Agenda  History of Mississippi’s Corrosion Control Law  MSDH Development of the Target pH Calculation  Sample Calculation Exercise  Other Corrosion Control Decisions

3. Mississippi’s Corrosion Control Law  MS Code 41-26-8. Requirements for construction and operation of public water systems; role of director (2)(h) Those public water systems determined by the director to be appropriately providing corrosion control treatment shall effectively operate and maintain the system’s water treatment facilities in order to continuously provide the optimum pH of the treated water or optimum dosage of corrosion inhibitor

4. History of Mississippi’s Corrosion Control Law  Customer complaints from a water system in north Mississippi  MSDH took samples  Did periodic checks of pH in the distribution  Lead to a hearing with the PSC

5. History of Mississippi’s Corrosion Control Law  2002 HB 935 (Rep Warner F. McBride, District 10) Introduced 41-26-8 (2)(h) The director shall identify those public water systems appropriately designed and constructed to provide corrosion control treatment, either pH adjustment or addition of corrosion control inhibitors, to provide their customers. The director shall further determine the optimum pH of the treated water or optimum dosage of corrosion control inhibitor for those public water systems determined to be appropriately providing corrosion control treatment and the director shall provide annually official written notification to those water systems of this optimum pH or optimum dosage. Those public water systems determined by the director to be appropriately providing corrosion control treatment shall effectively operate and maintain the system’s water treatment facilities in order to continuously provide this optimum pH or optimum dosage.

6. History of Mississippi’s Corrosion Control Law (cont.)  2002 HB 935 (cont.) House Committee Substitute 41-26-8 (2)(h) Those public water systems determined by the director to be appropriately providing corrosion control treatment shall effectively operate and maintain the system’s water treatment facilities in order to continuously provide the optimum pH of the treated water or optimum dosage of corrosion control inhibitor. Senate Amendment Added This paragraph shall repeal on July 1, 2005.

7. History of Mississippi’s Corrosion Control Law (cont.)  2005 HB 683 Rep D. Stephen Holland, District 16 Extended the repealer to July 1, 2007  2007 HB 928 Rep D. Stephen Holland, District 16 Extended the repealer to July 1, 2010  2010 SB 2743 Sen T.O. Moffatt, District 52 Removed the repealer

8. Corrosion control  Electrochemical reaction by which metal is attacked Factors causing corrosion ○ Carbon Dioxide ○ Hydrogen Sulfide ○ Galvanic series (type of metal) Cause of many metal line failures Most active metal gives up electrons to the least active – most active metal corrodes -Ex1: aluminum corrodes to stainless steel -Ex2: mild steel corrodes to copper -Ex3: Brass corrodes to copper

9. Corrosion control Factors effecting corrosion ○ Dissolved oxygen ○ Total dissolved solids ○ High alkalinity with soft water ○ Temperature ○ Stray current ○ Bacteria Coatings and films ○ Alkalinity and pH adjustment ○ Deposition of calcium carbonate ○ Corrosion inhibitors and sequestering agents

10. Stabilization  Is stable when it neither dissolves nor deposits calcium carbonate  Accomplished by raising pH (lime, soda ash sodium hydroxide) and adding polyphosphates  Lime for soft waters (lacking calcium  Soda ash or sodium hydroxide (caustic soda) for hard water  Langelier Saturation Index- testing stability Positive - deposition Negative - corrosive  Thin coating protects pipes

11. Stabilization  Polyphosphates prevent precipitation of Fe, Mn, and Ca  Dose at 2 mg/l for each mg/l of Fe & Mn  Add after filtration (most of the time)  Careful study should be done before installation of phosphate treatment  Polyphosphates can break down into simple phosphates

12. Development of the Target pH Calculation  Langlier Saturation Index (LSI) LSI = pH – pH s ○ pH is the final pH of the water ○ pH s is the saturation pH Calculated from total dissolved solids, temperature, alkalinity, and calcium contents of the water pH s = (9.3 + A + B) - (C + D) -A = (Log10[TDS] - 1)/10 -B = -13.12 x Log10(°C + 273) + 34.55 -C = Log10[Ca 2 + as CaCO 3 ] - 0.4 (Ca 2 + as CaCO 3 is also called Calcium Hardness and is calculated as=2.5(Ca 2 +)) -D = Log10[alkalinity as CaCO 3 ]

13. Target pH Calculation Procedure  Data to collect Raw Water Hardness (Ca + Mg) Raw Water Total Alkalinity as CaCO3  Data to measure Aerator Effluent pH

14. Target pH Calculation Procedure where pH = pH of the aerator effluent Alk = Alkalinity (T) as CaCO 3 CO 2 = concentration of carbon dioxide in mg/L 3.2 x 10 -7 is a calculated constant based on an average temperature (66.5 o F) to represent the typical temperature of water in plumbing.

15. Target pH Calculation Procedure If a residual CO 2 is calculated to be less than 10 mg/L from the effluent aerator pH, then the amount of CO 2 that must be used in the further calculations is 10. Ideally, aerators are not efficient enough to produce a CO2 residual of less than 10 mg/L.

16. Target pH Calculation Procedure Calculate the amount of Hardness and/or Alkalinity that is added to the water from the addition of lime, soda ash, or caustic soda using the residual CO 2 that was calculated/determined.  For lime addition: Calcium Hardness added = 1.351 X [CO 2 ] Alkalinity added = 1.615 X [CO 2 ]  For soda ash addition: Alkalinity added = 2.5 X [CO 2 ]  For caustic soda addition: Alkalinity added = 1.894 X [CO 2 ]

17. Target pH Calculation Procedure  Calculate the Total Hardness after chemical addition Lime Addition ○ Total Hardness = Raw Hardness + Ca Hardness Added Soda Ash or Caustic Soda Addition ○ Total Hardness = Raw Hardness  Calculate the Total Alkalinity after chemical addition Lime, Soda Ash, or Caustic Soda Addition ○ Total Alkalinity = Raw Alkalinity + Alkalinity Added

18. Target pH Calculation Procedure Calculate the Target pH  For Total hardness > 10 mg/l as CaCO3 Target pH = 9.7 + 1.85 –log[Total hard] – log[Total Alk]  For Total hardness < or = 10 mg/l as CaCO3 Target pH = 9.7 + 1.85 – 1.0 – log[Total Alkalinity ]  Total Hardness and Alkalinity as CaCO3 after chemical addition

19. Example Calculation using Lime  Raw water Ca+Mg Hardness as CaCO3 = 13 CO2 = 56 Total Raw Water alkalinity = 13  Analysis of the aerator effluent pH by the field engineer is 6.3  The treatment plant is using lime for corrosion control treatment

20. Example Calculation using Lime  Step 1 – Calculate the residual CO2

21. Example Calculation using Lime  Step 2 – Calculated Hardness and Alkalinity added from chemical addition Ca hardness add = 1.351 x res CO2 = 1.351 x 20.3 = 40.4 Alkalinity added = 1.615 x residual CO2 = 1.615 x 20.3 = 45.8

22. Example Calculation using Lime  Step 3 – Calculated Total Hardness and Alkalinity added from chemical addition Total hardness = raw water Hardness + Ca hardness added = 13 + 40.4 = 53.4 Total Alkalinity = raw water alk + Alk added = 13 + 45.8 = 58.8

23. Example Calculation using Lime  Step 4 – Calculate the Target pH Since the total hardness after lime addition > 4 (53.4 > 4), then the following equation is used pH = 9.7 + 1.85 – log[total hardness] – log[total alkalinity] pH = 9.7 + 1.85 – log[53.4] – log[58.8] = 8.28  Conclusion The target pH for this treatment plant while they are using lime for corrosion control is 8.3

24. Example Calculation using Soda Ash  Raw water Ca+Mg Hardness as CaCO3 = 13 CO2 = 56 Total Raw Water alkalinity = 13  Analysis of the aerator effluent pH by the field engineer is 6.3  The treatment plant is using soda ash for corrosion control treatment

25. Example Calculation using Soda Ash  Step 1 – Calculate the residual CO2

26. Example Calculation using Soda Ash  Step 2 – Calculated Hardness and Alkalinity added from chemical addition Alkalinity added = 2.5 x residual CO2 = 2.5 x 20.3 = 50.75

27. Example Calculation using Soda Ash  Step 3 – Calculated Total Hardness and Alkalinity added from chemical addition Total hardness = raw hardness = 13 Total Alkalinity = raw water alk + Alk added = 13 + 50.75 = 63.75

28. Example Calculation using Lime  Step 4 – Calculate the Target pH Since the total hardness after lime addition > 4 (53.4 > 4), then the following equation is used: pH = 9.7 + 1.85 – log[total hardness] – log[total alkalinity] pH = 9.7 + 1.85 – log[13] – log[63.75] = 8.63  Conclusion The target pH for this treatment plant while they are using soda ash for corrosion control is 8.6

29. Compliance Decisions  For lime, soda ash, or caustic soda addition, compliance is given for finished water pH within 0.5 units of the target pH.  For phosphate addition, compliance is given for monitoring of the total phosphorous with a pH close to 7.5

30. Additional Information Stay in touch Linked In: www.linkedin.com/in/hgongjrpe18005www.linkedin.com/in/hgongjrpe18005 Email:Harry.Gong@msdh.ms.govHarry.Gong@msdh.ms.gov hgongjr@gmail.com Phone:601-576-7518 or (cell) 601-573-0002 Follow the Alabama/Mississippi Section of AWWA on Facebook: http://www.facebook.com/almsawwa