1. Project Title
Phosphate-Free Inorganic Inhibitors for Water Supplies to Mitigate Lead Release and Corrosion
PI: Yin Wang
Student: Soheil Hosseini
Department of Civil and Environmental Engineering
University of Wisconsin-Milwaukee
11/8/2018

2. 2016 Project Goals & Scope
Overall Goal: Investigate the capability of a variety of phosphate-free inorganic inhibitors in minimizing lead release from aged metallic lead materials under conditions relevant to Chicago and Milwaukee drinking water distribution.
Specific Target Performance:
Inhibitor formulations to perform similarly to orthophosphate.
Specific Objectives:
Identify the optimum inorganic inhibitor formulations and concentrations.
Evaluate the impact of changing disinfectants on the performance of inhibitors .
Elucidate the mechanism that governs the interaction of lead materials and the optimum inhibitor formulations.
11/8/2018

3. Literature Review
Lead-containing materials (Pb0) are widely present in drinking water distribution systems.
More than half of the US drinking water utilities use phosphate inhibitors.
Burden of orthophosphate on downstream wastewater treatment plants
Phosphate-free methods for corrosion control and lead release prevention.
Organic, transition metal oxyanions, and rare-earth metal corrosion inhibitors.
11/8/2018

4. Water quality parameter
Approach
Three classes of inorganic compounds
Water quality parameter
Unit
Artificial water pH -
7.7
Total hardness
mg/L as CaCO3
140
Total alkalinity
117
[Cl-]
mg/L 15
[SO42-] 30
[PO43-]
1.4
Free chlorine
mg/L as Cl2 1
Chloramines
Metal cations (2):
SnSO4 (2 mg/L as Sn)
ZnSO4 (2 or 4 mg/L as Zn)
Oxyanions (3):
Na2SiO3, Na2Si3O7 (20 mg/L as SiO2)
Na2B4O7 (5 mg/L as BO3)
pH/alkalinity adjusting agent (1):
NaOH (pH = 8.5 or 9.2)
2×1×0.05 cm coupons
Total area is 4 cm2 per coupon
11/8/2018

5. Approach Coupon conditioned for ~3 months to develop corrosion scales.
Switch phosphate to phosphate-free inhibitors on week 1 (Mar 28).
Switch disinfectant from free chlorine (1mg/L) to mono-chloramine (2 mg/L) on week 10 (May 30).
Change inhibitor concentrations or pH on week 19 (Aug 1).
14 test reactors, 2 w/o orthophosphate, 3 w/ orthophosphate
“Dump-and-fill” mode: Change water Monday, Wednesday, and Friday
Monitor pH and free chlorine or mono-chloramine concentration daily
Collect samples 2 times per week for ICP-MS lead analysis
11/8/2018

6. Project Timeline & Milestones
11/8/2018

7. Performance of Inhibitors
pH 7.7 (except pH 9.2), w/ free chlorine (1 mg/L as Cl2), 48 hr stagnation, total lead
pH adjustment (pH 9.2) works well (unexpected lead release disappeared after long time).
SnSO4 exhibits some level inhibition (require time to develop corrosion scales).
11/8/2018

8. Effect of Disinfectant
Switch disinfectant from free chlorine (1mg/L as Cl2) to mono-chloramine (2 mg/L as Cl2)
Total lead, 48 hr stagnation, 2 weeks ave. (free chlorine, before switch; monochloramine, after switch)
Switch free chlorine to mono-chloramine increased lead release, especially in blank and SnSO4 conditions (possibly destabilize PbO2 corrosion products).
pH can effect inhibit lead release in the presence of mono- chloramine.
11/8/2018

9. Effect of Silicates Starting week 14:
No pH adjustment for Na2SiO3 and Na2Si3O7.
Mono-chloramine
Total lead, 48 hr stagnation
Addition of silicates (without adjusting pH back to 7.7) can effectively prevent lead release in relatively short term experiments, probably because of the increase of solution pH.
11/8/2018

10. Effect of pH and ZnSO4 Conc.
Starting week 19:
Increase ZnSO4 conc. from 2 to 4 mg/L as Zn with mono-chloramine (M).
Decrease pH for pH adjusting agent from 9.2 to 8.5 with free chlorine (F) and mono-chloramine as the disinfectant.
Total lead, 48 hr stagnation
Doubling ZnSO4 concentration inhibits lead release to some extent with mono-chloramine as the disinfectant.
Decreasing pH works well in the presence of free chlorine, while it enhances lead release with mono-chloramine.
11/8/2018

11. If Successful, What Is Needed for Commercialization?
TRL 3 – 4 by the end of this year.
Bench test for performance evaluation under various water chemistry conditions.
Pilot-scale experiments with the use of aged lead materials.
11/8/2018