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

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

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

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

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

Project Timeline & Milestones 11/8/2018

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

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

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

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

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