Anion Exchange for Drinking Water Treatment Michael Poulios, Aqua North Carolina William Dowbiggin, CDM Smith November 2015 2015 Annual Conference Raleigh, NC

What is Ion Exchange? Removing undesirable ions in water through a chemical reaction using an ion exchange resin

Regeneration of Dissolved Organic Carbon (DOC) Removal Resin Example Resins

Ion Exchange Description and Examples Undesirable ions are captured on reactive sites of resin Ions initially attached to resin are released into treated water Reversible reaction is most useful (recharge the resin) Cation exchange uses H+ or Na+ Anion exchange uses OH- or Cl- Definition Use a substitution reaction to remove ions Water treatment applications Examples: Softening(Ca2+, Mg2+) or other cation exchange Organics removal (Anion Exchange) As the name suggests, contaminant are removed through the exchange of ions. Undesirable ions (contaminants) are removed from water through a chemical substitution reaction. Undesirable ions are captured on reactive sites on the resin while ions initially attached to the resin are simultaneously released. This substitution reaction is reversible which allows the resin to regenerated. Ion exchange is useful for softening and organics and color removal in water treatment, whereas wastewater and industrial applications using ion exchange focus on chemical recovery or contaminant removal. Anion Removal (Nitrate, Perchlorate, Arsenic, Selenium, Chromium) Wastewater/Industrial applications Other uses include chemical recovery Contaminant (i.e. heavy metals) removal

Inside of the Ion Exchange Bed Typical arrangement Specified cubic feet of ion exchange resin (e.g. zeolite for softening) Freeboard for bed expansion during a backwash Gravel and underdrain or other media support system

Anion Exchange Process Anions in decreasing order of selectivity: Raw Water NaCl to Regenerate DOC Chromate Phosphate Perchlorate Sulfate Carbonate Bromide Iodide Arsenate Nitrate Chlorate Hydroxide Bromate Nitrite Chloride Bicarbonate Fluoride Spent Backwash Water Anion Exchange Resin Low Organic Matter Treated Water Backwash Water Spent Brine To Waste

Example Order of Anion Elution from another CDM Smith Project All exchanged ions peak except the most-preferred ion

The Aqua Castle Bay Subdivision Water System is a 150 gpm Groundwater System near Hampstead NC just north of Wilmington The Castle Bay Water system is a groundwater system for drinking water supply located near Wilmington North Carolina that is operated by Aqua NC. The current system has two wells and two iron removal filters rated for 75 gpm each (150 gpm combined). The iron removal filter approach uses chlorine for oxidation. System water demand is about 35 gpm on average (about 50,000 gallons per day). The wells are typically operated 8 hours per day, 5 days per week. The system has ___ million gallons of storage. Mr. Don Williams Coastal Area Manager 105 Hampstead Village Building 24-I Hampstead, NC 28443 office: 910-270-1412 Fax: 910-270-3147 Cell: 919-625-2533

Castle Bay Anion Exchange Project Drivers High concentrations of disinfection byproducts A desire to avoid chloramines and associated nitrification control issues given the system has high residence time

Castle Bay Anion Exchange Project Phases Bench study and testing of resin isotherms to screen resins and obtain data for planning pilot testing Pilot testing of two short-listed resins to confirm suitability and determine guarantees for bidding Design Construction and Start-up

Bench Test Results - TOC mg/L vs. mL Resin Added mL of Resin Added

Bench Test Results - UV-254 Absorbance vs. mL Resin Added UV-254 Abs. (cm-1) mL of Resin Added

Bench Test Results - Color vs. mL Resin Added Color (PCU) mL of Resin Added

Bench Isotherm Preliminary Calculated Values Resin K 1/N R2 Ld DR VR (mg/g) (g/mL) (L/L) R.Tech SIR- 22P-HP 10.28 0.98 0.76 39.85 1.200 3288 R.Tech SBACR-HP 3.42 1.28 0.85 20.19 3029 Thermax A- 72 3.26 0.93 0.64 11.84 1.100 1254 Thermax A- 30 10.62 1.35 0.87 68.86 7291 Purolite A- 860 9.39 1.45 0.79 70.00 1.065 6710

Figure 2 Raw Water Test – TOC vs. Run Time

Regenerated at 163 hours Figure 3 Filtered Water Feed to Resin – TOC vs. Run Time Regenerated at 163 hours

The Resin is Piped for Raw Water or Filtered Water Feed-Initially to use Raw Water because: Purolite ended up the selected media supplier, and they recommended treating the raw water with the resin based on prior experiences, concern over the chlorine residuals, and the pilot data for this project. Chlorine degrades the anion exchange resin and chlorine residuals coming out of the iron filters have been highly variable and up to 1.63 mg/L reaching the pilot units which is far above Purolite’s recommended 0.2 mg/L max chlorine reaching the anion exchange resin. Even Tonka, who recommended trying downstream on filtered water, concurred that it should be on raw water after the pilot test on filtered water. After the iron removal filters, the Tonka unit had clogging (pressure increases) quickly dropping flows and requiring regeneration then had clogging again.

The Resin is Piped for Raw Water or Filtered Water Feed-Initially to use Raw Water because (continued): Iron removal in the anion exchange resin was found to be low when operated on the raw water, but up to 0.44 mg/L in the Tonka unit and up to 0.34 mg/L in the Purolite unit when operated after the iron removal filter. These levels of iron removal in the AER resin indicate quick iron fouling potential and correspond to the observed clogging (pressure increases and flow decreases).  Total run time on the log sheet is 817 hours for raw water.  The run time for post iron filters was 588 hours.  The Tonka unit reportedly also had a regen/wash before even reaching the 588 hours due to the clogging.    Anion resin on the raw water helps DBPs by removing the organics before the first chlorine dose.

Planning for the Anion Exchange Resin Operations Based on the pilot testing and prior projects, the vendors suggested planning on regenerating the media once a week typically. The necessary regeneration frequency will increase with age and fouling. The salt required for regeneration was reported to be 8 to 10 lb/cubic foot of media. The final installation is to have 87 cubic feet of media including all three vessels. Consequently, the amount of salt used per regeneration of all three vessels was estimated to be about 700 to 870 lb of salt per regeneration of all three vessels. Salt cost is about $ 0.12/lb, and the vendor indicated about 3,200 gallons of water would be used in each regeneration. The resin is guaranteed to last at least a week between regenerations.

Design, Construction and Costs The design included plan and profiles and a detailed technical specification with performance requirements The purchase cost of the anion exchange system was approximately $ 140,000 with all items included. Potential cost saving measures could include strategies such as operating just one or 2 beds at a time pending DBP levels. In conclusion, the anion exchange resin should do an excellent job of removing the organic precursors of disinfection byproducts. Cost control for the resin will be influenced by careful operations to prevent fouling while still being frugal with respect to labor and chemical costs.

Design - Anion Exchange Vessels

The Anion Exchange Vessels at Castle Bay Water System

Water Softening System at Castle Bay Water System

Conclusions The anion exchange resin should do an excellent job of removing the organic precursors of disinfection byproducts. Cost control for the resin will be influenced by careful operations to prevent fouling while still being frugal with respect to labor and chemical costs. Potential cost saving measures could include strategies such as operating just one or 2 beds at a time pending DBP levels.

Questions? Michael Poulios, PE LEED Aqua North Carolina (919) 653-6965 William B. Dowbiggin, PE BCEE CDM Smith (919) 623-7964 dowbigginwb@cdmsmith.com