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Edwin C. Tifft, Jr. Water Supply Symposium
William Becker, PhD, PE, BCEE
Corrosion: Making Sure you have it Under
Control
Outline
• Background
• Causes of high lead levels
• Corrosion control
• Inhibitors
• CSMR
• Unintended consequences
• An approach for conducting corrosion control
studies
• Recommendations
March 2016
Acknowledgments:
• Becki Rosenfeldt
• Michael Schock
• Marc Edwards
• Roger Arnold
JAWWA July, 1989
CorrosionLead and Copper Release
Water Loss and Leaks
Asset Management
Water Quality
Optimization
Simultaneous Compliance
Customer Relations
Corrosion in Distribution Systems
Holistic Distribution System Management
Sources of Lead
Locations of lead in the Flint Water System (City of Flint Oct. Quarterly Water Quality Report, https://www.cityofflint.com/wp-content/uploads/Quarterly-Water-Quality-Report_Oct-15.pdf)
Particles
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.
• 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
Optimum Corrosion Control Treatment (OCCT)
Types of Scale on Pb Pipe
Simple carbonate or hydroxycarbonate Pb(II) mineral
Simple Pb(II) orthophosphate mineral
Simple PbO2 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
9
Michael Schock: Simultaneous Compliance: Myth versus Reality
Photograph of interior of NYC distribution system pipe showing a very
thin brown surface layer with a thick white layer beneath.
Scale Analysis – Existing NYC Lead Pipe
Lead Pipe
L2
L1 Plattnerite – PbO2 and Pyromorphite – Pb5Cl(PO4)3
Hydrocerussite - Pb3(CO3)2(OH)2 and some Pyromorphite - Pb5Cl(PO4)3
Lead Scale Analysis
Two distinct layers: L1 – a thin grey/brown scale
L2 – a thick white scale
WQ Factors Affecting Metal Release
12
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 versus Reality
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)
Treatment Can Affect Pb Release
13
14
Chemical Changes Cause Dissolution of PbO2
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
–.8
–.6
–.4
–.2
.2
.4
.6
.8
1.0
pH
Eh (
volt
s)
Pb++
Pb
(OH
) 42
-Pb
CO
3°
Pb
(CO
3) 2
2-
--
Pb
3(C
O3) 2
(OH
) 2(s
)
Pb metal
PbO2 (plattnerite)
DIC = 18 mg C/LPb = 0.010 mg/L
1.2
0.0
-1.0
Drop in pH at surface from treatment change, rxns,
nitrification, etc.
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
Michael Schock: Simultaneous Compliance: Myth versus Reality
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
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
Film formation prevents galvanic cell reaction
Pipe wall
Detrimental Impacts of SequestrationEffect of polyphosphate on orthophosphate dose response
(Colin Hayes, Swansea Univ.)
Median Pb emissions (μg/l) after 30 min
contact with new Pb pipe at 25oC
Be careful not to overdose polyphosphate, or hydrocerussite(hydrated lead carbonate) protective coatings will be damaged
o-PO4 dose Zero poly-P 0.2 mg/l poly-P 1.6 mg/L poly-P
0 142 143 281
1 3 19 54
2 3 12 51
3 3 10 44
4 3 9 32
Michael Schock: Simultaneous Compliance: Myth versus Reality
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
Flint
Water
is very
corrosive.
Detroit
water is
not.
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.
Corrosion pilot unit
Pilot testing is recommended to evaluate
alternative corrosion inhibitors
Typical corrosion pilot unit
Coupon Study
Corrosion pilot unit
Copper piping with 50/50 lead solder for LCR
samples
Continuous Flow Loops
24
Stagnation Testing
LEAD COPPER
Corrosion Control Treatment
Contains useful
flow charts to help
select viable
treatment options
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, non-porous layer
Carbonate Precipitation Not Considered An
Effective Strategy for LT-LCR Compliance
Lead and Copper Control Treatment Strategies
Systems not adding phosphate
Raise pH and/or
alkalinity
Add phosphate
Add phosphate and adjust
pH
Systems adding
phosphate
Boost phosphate
Adjust pH
Systems adding poly-
phosphate
Adjust pH
Switch to ortho-
P
Figure 2.3 from EPA OCCT Manual (Buffer Intensity as a
Function of pH at Different DIC Values (Clement and
Schock, 1998b, Figure 1) )
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
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
6 6.5 7 7.5 8 8.5 9 9.5
Le
ad
So
lub
ilit
y (
mg
/L)
pH
2 mg/L PO4, 5 mg/L Alk as CaCO32 mg/L PO4, 15 mg/L Alk as CaCO33 mg/L PO4, 5 mg/L Alk as CaCO33 mg/L PO4, 15 mg/L Alk as CaCO3
Increase Target pH from 7.2 to 7.5-7.6, Limit pH Fluctuations, and
Increase Target PO4 Dose from 2 ppm to 3 ppm (Schock, 1998).
What are the unintended consequences we need to consider?
Potential LT-LCR Unintended Consequences
Description of Potential UICOCCT Strategy
pH/Alkalinity Adjustment 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
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.
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.
Recommendations
For simultaneous compliance issues consider:
DBP precursor removal vs. chloramination
Iron/Manganese removal vs. sequestration
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
System has existing
OCCT
Exceeded LCR
AL and/or WQ
parameters
outside optimum
range for CCT?
Yes
Conduct Tier 1 Assessment (Self assessment)
- 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
Are corrosion
control
treatment
improvements
still needed?
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)
No
Implement changes to existing
CCT identified in Tier 1 Self
Assessment
No
Considering a
changethat may affect
CCT? (supply,
treatment,
distribution)
NoSTOP
Yes
STOP
Adapted from:
• AWWA Water Industry Technical Action Fund. “Managing
Lead and Copper Rule Corrosion Control Practices to Avoid
Unintended Consequences.” Malcolm Pirnie, Inc. November
2006.
• Brown, R., Mctigue, N., and Cornwell, D. Strategies for
assessing optimized corrosion control treatment of lead and
copper. Journal AWWA, 105(5): 62-74.
