KIMBERLY GUPTA, PE PORTLAND WATER BUREAU

ManagingHypochloriteto ReduceChlorateFormation:A Utility CaseStudyK I M B E R LY G U P TA , P EP O R T L A N D WAT E R B U R EA UCO-AUTHOR: YONE AKAGI, PEAW WA P N W SK E N N E W I C K , M AY 5 , 2 0 1 7

Presentation OutlineBackground on chlorateFactors affecting chlorateformationPWB’s experience withchlorate UCMR Results Study evaluating chlorateformation in low salt hypovs standard hypo

Why Do We Care About Chlorate?Chlorate is an unregulated disinfectant by product thatoccurs when using hypochlorite or chlorine dioxide fordisinfectionChemicals used for drinking water treatment is thedominant source of exposure to chlorate Chlorate compounds are also used in agriculture asherbicides or desiccantsRoute of toxicity is through ingestion and inhalation Decrease thyroid function Impairment of blood’s ability to carry oxygen Some toxicological reports have shown that chlorate hassimilar toxic modes of action as perchlorateWidespread in drinking water at relevant concentrations

Chlorate RegulationsThere is no federal regulation forchlorate in drinking water at this time EPA has established a Health Reference of210 µg/LCalifornia has set an action level forchlorate at 700 ug/LWHO: 0.7 mg/L provisional guidelineCanada: 1 mg/L Maximum AcceptableConcentrationControl of chlorate formation is bestsince there are no widely acceptedtreatment methods for chlorate

Chlorate Occurrence (ICR)Source: Alfredo et al., 2014

Chlorate Occurrence: ICR and UCMR3Source: Six-Year Review 3 Technical Support Document for Chlorate (EPA, 2016)

Chlorate Occurrence: UCMRSource: Six-Year Review 3 Technical Support Document for Chlorate (EPA, 2016)

Chlorate FormationDisinfection with the following: Chlorine dioxide Bulk hypochlorite On-site generated hypochloriteOzonation/UV treatment ofchlorinated waters can lead tochlorate formation

Sodium HypochloriteSodium hypochlorite is a commonly used source ofchlorine for water treatment Has been estimated that approximately 31% of WTPs usebulk hypochlorite for disinfection (Snyder et al., 2009) Use has increased due to safety concerns regardingtransporting and storing chlorine gasIt is effective, relatively easy to use, and readilyavailable

Sodium Hypochlorite ContinuedThere are a number of disadvantages to using sodiumhypochlorite Multiple contaminants can occur in hypochlorite solutionsincluding bromate, chlorite, chlorate, and perchlorate Sodium hypochlorite decomposes with time, heat, andexposure to metals such as iron, copper, nickel, etc. As hypochlorite degrades, perchlorate and chlorate areformed

Factors Contributing to the Formationof Chlorate in Hypochlorite SolutionsHypochlorite strength Higher strength solutions will form more chloratepH pH range to reduce chlorate formation is 11-13Ionic strength Higher ionic strength favors higher reaction ratesPresence of some metals Some metals such as iron will increase thedecomposition rate of hypochlorite

Portland Water Bureau Overview Serves approximately 966,000 people – approximately 25% of Oregon 20 wholesaler customers which comprise approximately 42% of systemdemand

Monitoring Hypochlorite in thePWB’s System – UCMR3 Results As part of UCMR3, Portland testedprimary and backup supplies forchlorate Treated water from the surface watersupply was non-detectable forchlorate in any of the samples A chlorate concentration of 3000 µg/Lwas measured in treated water fromthe groundwater supply

What Happened?The groundwater facility is anemergency source of supply so it mustbe able to be brought online as soon aspossible Sodium hypochlorite must be stored onsite at the groundwater treatmentfacility at all timesChlorate formation is a function of time As the solution ages, chlorate increasesand FAC decreases

Implemented Strategies to DecreaseChlorate FormationDilute hypochlorite solutions immediately after delivery Diluting a 2M solution in half decreases the formation ofchlorate by a factor of 7Ensure pH of 11-13 of stored hypochlorite solutions(even after dilutions)Ensure transition metal ions are low (purchase filteredhypochlorite solutions)Tightened the hypochlorite specification to improveinitial hypochlorite conditionsStore hypochlorite solutions at low temperatures(60 F/15 C recommended) Decreasing the storage temperature by 5C decreases formationby a factor of 2

High Strength Low Salt HypochloriteAccording to the vendor, the highstrength, reduced salt hypochloritewould improve the half life of thesodium hypochlorite by a factor of 2compared to traditional sodiumhypochlorite at the sameconcentration and temperatureReduced salt in the sodiumhypochlorite makes the productapproximately 2 times more stablethan standard hypochloriteWe conducted a trial to evaluate this

Results: Low Salt vs Standard 2015 12/12/2015 1/31/2016 3/21/2016 5/10/2016 6/29/2016 8/18/2016LS Hypo: ClO3Standard Hypo: ClO3Free Available Chlorine in Low Salt Hypochloritevs Standard Hypochlorite Bulk Solutions60000Chlorine (mg/L)Obtained 5 gallons of lowsalt hypochlorite from thevendorAt the same time, weordered a new shipment ofour standard hypochloriteStored the low salt hyponear our existinghypochlorite storage tanksSampled the low salt andstandard hypochlorite eachmonth and analyzed forchlorate, pH, and FACChlorate in bulk chemical (mg/L)Chlorate Formation in Low Salt Hypochlorite vsStandard Hypochlorite Bulk Solutions5000040000300002000010000010/23/2015 12/12/2015 1/31/2016 3/21/2016 5/10/2016 6/29/2016 8/18/2016LS Hypo: ClStandard Hypo: Cl

Results: Low Salt vs StandardHypochlorite - Full Scale Test

Recommendations Based on OurExperienceImplement strategies to reducechlorate formation Use fresh hypochlorite when possible Dilute hypochlorite upon delivery Store at lower temperatures Control the pH (11-13) Control the removal of metals thatincrease hypochlorite degradation

Recommendations Based on OurExperienceDouble check your hypochlorite specificationsEstimate the chlorate formation potential of yourhypochlorite Determine how long it takes you to use up a batch ofyour hypochlorite Use the AWWA chlorate tool to estimate how muchchlorate (and perchlorate) the hypochlorite you haveonsite is producing Use the tool to determine various dilutions to helpreduce chlorate formation Monitor to ensure your assumptions were correct

ResourcesThere are a lot ofvery helpfulresources out thereon this topic AWWAhypochloriteassessment tool

Resources ContinuedAWWA Journal Articlesand WaterRF StudiesAWWA Standard onHypochlorite StorageEPA 6 year review onchlorateWater RF and AWWAReports

Next StepsContinue practicing strategies tominimize chlorate formation in bulkhypochloriteConsider switching to a low salthypochloriteContinue monitoring ourhypochlorite as we receive it andmonthly to ensure that chlorateconcentrations do not reachunacceptable levels

QUESTIONS?Contact informationKimberly GuptaPortland Water BureauKimberly.gupta@portlandoregon.gov

3/21/2016. 5/10/2016. 6/29/2016. 8/18/2016. Chlorate Formation in Low Salt Hypochlorite vs Standard Hypochlorite Bulk Solutions LS Hypo: ClO3. Standard Hypo: ClO3. 0. 10000. 20000. 30000. 40000. 50000. 60000. 10/23/2015. 12/12/2015. 1/31/2016. 3/21/2016. 5/10/2016. 6/29/2016. 8/18/2016