Corrosion: Making Sure you have it Under Control

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1 Edwin C. Tifft, Jr. Water Supply Symposium Corrosion: Making Sure you have it Under Control William Becker, PhD, PE, BCEE

2 Outline March 2016 Background Causes of high lead levels Corrosion control Inhibitors CSMR Unintended consequences An approach for conducting corrosion control studies Recommendations

3 Acknowledgments: Becki Rosenfeldt Michael Schock Marc Edwards Roger Arnold JAWWA July, 1989

4 Corrosion in Distribution Systems Asset Management Water Quality Optimization Water Loss and Leaks Simultaneous Compliance Lead and Copper Release Corrosion Customer Relations Holistic Distribution System Management

5 Sources of Lead Locations of lead in the Flint Water System (City of Flint Oct. Quarterly Water Quality Report, Report_Oct-15.pdf)

6 Particles

7 Holistic view Corrosion in water systems is a function of raw water quality, treatment, and distribution system operations. A true source-to-tap approach is needed to ensure optimum corrosion control treatment. To achieve OCCT overall process control and distribution system water quality optimization must also be achieved. OCCT is not an independent, separate process.

8 Optimum Corrosion Control Treatment (OCCT) Defined as: the corrosion control treatment that minimizes the lead and copper concentrations at users' taps while insuring that the treatment does not cause the water system to violate any national primary drinking water regulations. Much more than simply adjusting ph or adding phosphate Existing pipe scales are key Metal solubility is important factor 8

9 Types of Scale on Pb Pipe Simple carbonate or hydroxycarbonate Pb(II) mineral Simple Pb(II) orthophosphate mineral Simple PbO 2 solid phase, by itself or mixed with Pb(II) phases Mix of Pb(II) phases Protective diffusion barrier materials Could be insoluble amorphous Pb(II) phase Adherent non-pb phase Surface fouling deposit Primarily not made of lead, usually not crystalline Lead may sorb to surface Michael Schock: Simultaneous Compliance: Myth versus Reality 9

10 Scale Analysis Existing NYC Lead Pipe Photograph of interior of NYC distribution system pipe showing a very thin brown surface layer with a thick white layer beneath.

11 Lead Scale Analysis Two distinct layers: L1 a thin grey/brown scale L2 a thick white scale L1 L2 Plattnerite PbO2 and Pyromorphite Pb5Cl(PO4)3 Hydrocerussite - Pb3(CO3)2(OH)2 and some Pyromorphite - Pb5Cl(PO4)3 Lead Pipe

12 WQ Factors Affecting Metal Release Temperature ph & stability (buffering) ORP/corrosion potential Type and amount of disinfectant Dissolved oxygen Alkalinity/DIC Orthophosphate Polyphosphate (amount and type) Chloride Sulfate Sorptive surfaces downstream of LSLs (ie. galvanized interior pipe) Iron (deposition and corrosion) Calcium Manganese Aluminum NOM (type, amount) Amount of mixing of WTPs or sources Ammonia Hydrogen Sulfide Silica Microbial activity (nitrification and other) Michael Schock: Simultaneous Compliance: Myth 12 versus Reality

13 Treatment Can Affect Pb Release Iron or manganese post-precipitation Alum carry-over Anion exchange for U, As, NOM, etc. Sequestration of Fe, Ca, Mg, Mn by polyphosphate or blended phosphate Change in amount or type of disinfectant Oxidation/filtration for Fe or Mn removal Optimum or enhanced coagulation Changes in type of coagulant Changes in coagulant dosage Aeration Season water quality changes: ph, alkalinity, chloride, sulfate, NOM, temperature GAC for DBP control Ammonia oxidation Tight membrane (RO or NF) Relining/replacement of mains (chemical changes or physical disturbances) 13

14 Eh (volts) PbCO 3 Pb 3 (CO 3 ) 2 (OH) 2 (s) Chemical Changes Cause Dissolution of PbO PbO 2 (plattnerite) Drop in ORP from treatment change or DS oxidant demand Disinfectant demand in DS must be controlled and enough free chlorine consistently maintained throughout LSL area Pb ++ Drop in ph at surface from treatment change, rxns, nitrification, etc. Pb metal Pb(CO 3 ) Pb(OH) 4 2- DIC = 18 mg C/L Pb = mg/l ph Michael Schock: Simultaneous Compliance: Myth versus Reality 14

15 Corrosion inhibitors The use of phosphate corrosion inhibitors is common in drinking water. Purpose is to promote the formation of insoluble scales that prevent lead and copper from leaching from pipes. The most common corrosion inhibitors used are: Zinc orthophosphate Orthophosphate Polyphosphates Phosphate Blends Silicates

16 Passivation is the key for most utilities Passivation is the formation of lead and copper carbonate films calcium carbonate film metal oxide film metallic carbonate film Phosphate/metallic/carbonate film water Pipe wall Film formation prevents galvanic cell reaction

17 Detrimental Impacts of Sequestration Effect of polyphosphate on orthophosphate dose response (Colin Hayes, Swansea Univ.) Median Pb emissions (μg/l) after 30 min contact with new Pb pipe at 25 o C o-po4 dose Zero poly-p 0.2 mg/l poly-p 1.6 mg/l poly-p Be careful not to overdose polyphosphate, or hydrocerussite (hydrated lead carbonate) protective coatings will be damaged Michael Schock: Simultaneous Compliance: Myth versus Reality

18 Edward s Chloride : Sulfate Mass Ratio Chloride : Sulfate Mass Ratio < 0.58 = no leaching > 0.58 = lead leaching Low Alkalinity also contributes to Problem High Alkalinity = no leaching Low Alkalinity = lead leaching Orthophosphate inhibitor can mitigate

19 Flint Water is very corrosive. Detroit water is not.

20 Corrosion Control: Approach Holistic view Evaluation Understand the first principles (theory) Desktop analysis source to tap Pipe loops, pipe rigs (use pipe from system) Recommendations Full scale implementation Monitoring Feedback Remember: There are no corrosion indices, surrogate pipe rigs, or water quality parameters, that can take the place of directly monitoring lead release.

21 Corrosion pilot unit Pilot testing is recommended to evaluate alternative corrosion inhibitors Typical corrosion pilot unit

22 Coupon Study

23 Corrosion pilot unit Copper piping with 50/50 lead solder for LCR samples

24 Continuous Flow Loops 24

25 Stagnation Testing LEAD COPPER

26 Corrosion Control Treatment Contains useful flow charts to help select viable treatment options

27 Three Corrosion Control Methods Originally Identified as Optimum in the Current LCR Carbonate Passivation ph/alkalinity balance Metal complexes on pipe surface Prevents metal release Inhibitor Addition Phosphates (orthophosphate or blends) Silicates Carbonate Precipitation Calcium carbonate coats pipe surface Does not form uniform, nonporous layer Carbonate Precipitation Not Considered An Effective Strategy for LT-LCR Compliance

28 Lead and Copper Control Treatment Strategies Systems not adding phosphate Systems adding phosphate Systems adding polyphosphate Raise ph and/or alkalinity Add phosphate Add phosphate and adjust ph Boost phosphate Adjust ph Adjust ph Switch to ortho- P

29 ph Highest buffer intensity at ph ~6.3 Minimum intensity between 8.0 and 8.5 The lower the buffer intensity the more ph variation is likely Figure 2.3 from EPA OCCT Manual (Buffer Intensity as a Function of ph at Different DIC Values (Clement and Schock, 1998b, Figure 1) )

30 Lead Solubility (mg/l) Increase Target ph from 7.2 to , Limit ph Fluctuations, and Increase Target PO 4 Dose from 2 ppm to 3 ppm (Schock, 1998) mg/l PO4, 5 mg/l Alk as CaCO3 2 mg/l PO4, 15 mg/l Alk as CaCO3 3 mg/l PO4, 5 mg/l Alk as CaCO3 3 mg/l PO4, 15 mg/l Alk as CaCO ph

31 What are the unintended consequences we need to consider?

32 Potential LT-LCR Unintended Consequences Description of Potential UIC ph/alkalinity Adjustment OCCT Strategy Phosphate Addition Increased scaling resulting in loss of hydraulic capacity or additional system maintenance Reduced distribution system disinfection performance Increased microbial activity in the distribution system Change in DBP speciation/concentrations and Joint Stage 2 DBPR and LT-LCR compliance Increased phosphorus loading at WWTP, with increased sludge production Altered metals loading to wastewater treatment plant Need for additional operator certification/staffing

33 Recommendations A corrosion control study should be performed under the following circumstances: If a new raw water source is activated If a new finished water supply is purchased (or if a utility will start selling finished water to a neighboring system) If chemical treatment processes are changed in the plant. This could include the following: Changing pre-oxidants Increasing chlorine dose Switching distribution system disinfectant to chloramine Changing coagulants or increasing coagulant dose significantly Study should consider seasonal effects Including raw water chloride levels Conduct well in advance of future treatment or operational changes that could impact lead or copper release.

34 Recommendations The chloride to sulfate mass ratio should be examined if any treatment changes are implemented. If this number increases above 0.58 then an orthophosphate inhibitor should be added. The best inhibitor to use if lead is the controlling issue is likely ortho-phosphate (phosphoric acid). A zinc based product usually does not work any better and costs more and can cause issues for the wastewater treatment plant. Polyphohphates can INCREASE lead levels as they work as a sequestering agents.

35 Recommendations For simultaneous compliance issues consider: DBP precursor removal vs. chloramination Iron/Manganese removal vs. sequestration

36 Recommendations Good operations: DO NOT cut inhibitor dosages to save money DO NOT cut ph adjustment to save money Keep feed equipment in good shape to minimize downtime STABILITY is key: Prevent random variations in raw or finished water sources Keep distribution system water quality stable Water age, tank turnover, flushing Want consistant ph, chlorine residual

37 QUESTIONS??? cell:

38 System has existing OCCT Exceeded LCR AL and/or WQ parameters outside optimum range for CCT? No Considering a change that may affect CCT? (supply, treatment, distribution) No STOP Yes Conduct Tier 1 Assessment (Self assessment) Yes - Review existing LCR monitoring and WQP data - Assess if WQ conditions are consistent w/ OCCT targets - Identify physical factors and changes (i.e. LSL/meter replacements) - Verify equipment is working properly - Check chemicals used (new product?, new formulation?, new vendor?) - Check, calibrate, replace instrumentation as needed - Verify standard operating procedures are being followed STOP Implement changes to existing CCT identified in Tier 1 Self Assessment No Are corrosion control treatment improvements still needed? Adapted from: AWWA Water Industry Technical Action Fund. Managing Lead and Copper Rule Corrosion Control Practices to Avoid Unintended Consequences. Malcolm Pirnie, Inc. November Brown, R., Mctigue, N., and Cornwell, D. Strategies for assessing optimized corrosion control treatment of lead and copper. Journal AWWA, 105(5): Yes Conduct Tier 2 Desktop Study/Additional Testing - Conduct desktop evaluation to determine if OCCT treatment is optimized for your system or establish new WQ criteria for OCCT - Determine ability to maintain finished WQ within identified target ranges - Conduct expanded monitoring and sampling of CCT and WQ parameters - Conduct pilot, pipe-loop, coupon testing (if needed or required by regulatory agency) - Assess potential Unintended Consequences that may result from implementing identified changes. Identify UIC mitigation strategies, if necessary - Evaluate emerging strategies to enhance treatment (i.e., distribution system optimization and/or improvements to enhance organics removal) Re-Optimize CCT (see Figure 3-4a)