Event July 1921 Iron amp Manganese Optimization Presented by Clayton Nicolardi PE Presentation Outline StandardsGoals Sources Basic Chemistry Treatment Strategies Removal Sequestration ID: 1024819
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1. National AWOP 9th Biennial Virtual EventJuly 19-21Iron & Manganese Optimization Presented by:Clayton Nicolardi, P.E.
2. Presentation OutlineStandards/GoalsSourcesBasic ChemistryTreatment StrategiesRemovalSequestrationAssessing Treatment EffectivenessMonitoringSampling2
3. Drinking WaterStandardsThe EPA has established secondary constituent levels (SCL) for iron and manganese of 0.30 and 0.05 mg/L, respectivelyIn 2004, they also set a non-enforceable lifetime health advisory (HA) level of 0.3 mg/L for chronic exposure to manganese and a 1-day and 10-day HA of 1.0 mg/L for acute exposure.3
4. Optimization Goals≤ 0.10 mg/L iron≤ 0.02 mg/L manganeseYour optimization goals may be more stringent4
5. OptimizationWhy optimize?Many water systems will begin to have problems before levels reach secondary levelsReduce discolored water complaintsImprove corrosion control treatmentImprove disinfection residuals by reducing demandIncrease longevity of infrastructure by reducing scale5
6. Sources of Iron and ManganeseGroundwaterAquifers pick up increased levels of iron and manganese as water filters through soils containing them in the recharge areas.Surface Water (Lakes and Rivers)Iron and manganese wash into impoundments from the watershed increasing in concentration over time.6
7. Physical States ofIron and ManganeseSoluble (in solution)InsolubleColloidal7Fraction that can be filteredFor removal through sedimentation or filtration we need to oxidize soluble iron and manganese to their insoluble forms.
8. Oxidation StatesIron (Fe):Fe+2 Ferrous (soluble)Fe+3 Ferric (insoluble) – ferric oxides (Fe2O3)Manganese (Mn):Mn+2 Manganous (soluble)Mn+3 Manganic (insoluble)Mn+4 (insoluble) – manganese dioxide (MnO2) 8
9. Oxidation ReactionsFe+0 Fe+2 + 2e-Fe+2 Fe+3 + 1e-Mn+0 Mn+2 + 2e-Mn+2 Mn+3 + 1e-Mn+3 Mn+4 + 1e-OxidationOxidationOxidationOxidationOxidation9
10. Forms in Source WaterGroundwaterIron and manganese are in the soluble form as groundwater is void of oxygen.Surface WaterIron and manganese can be in the soluble or insoluble form depending on whether they are exposed to oxygen or CO2.10
11. PretreatmentOxidationChlorinePermanganates (sodium/potassium)Chlorine dioxideOzoneAeration (non-chemical)pH AdjustmentCausticLime11
12. Chemical OxidationChemical oxidants can be used to either:Oxidize soluble iron and manganese to their insoluble forms;Recharge/restore adsorption properties of filter media (e.g. KNMnO4 for greensand and chlorine for microsand); orBoth12
13. AerationAeration can be used to:Oxidize soluble iron (not so practical for oxidizing soluble manganese)Help remove demand such as hydrogen sulfideIncrease pH by removing carbon dioxide13
14. Mixing/Destratification14
15. De-stratification15Fe2+Mn2+Warmer WaterColder WaterOxic LayerO2O2Anoxic LayerMn4+Fe3+Colder TemperaturesCO2CO2OxidationReduction
16. pH AdjustmentImprove coagulationOptimize oxidation of iron (lower pH) and manganese (higher pH)Achieve optimum pH for coagulants and organic polymersAchieve optimum pH for hydrogen sulfide removal and oxidation of iron and manganeseFacilitate softening16
17. Filter Media TypesDual media (anthracite/sand)Manganese greensandBirm™ (Burgess Iron Removal Method)AnthrasandPyrolusite 17
18. SequestrationSequestration does not remove iron and manganese - only keeps them in solution (Fe+2 and Mn+2)The objective of sequestration is to keep prevent soluble iron and manganese from oxidizing18
19. 19How it Works
20. SequestrantsPolyphosphates:Sodium acid pyrophosphateTetrasodium pyrophosphateTetrapotassium pyrophosphateSodium tripolyphosphatePotassium tripolyphosphateSodium trimetaphosphate andSodium hexametaphosphate20
21. Chemical EffectivenessAdequate mixingNeed adequate chemical dispersion before adding oxidantLocation of feeding pointShould be as close to the raw source as possibly and always before the chlorine feedTemperatureWater temperatures above 120ºF can lead to the dissociation of sequestering complexes (e.g. water heaters)21
22. Chemical EffectivenesspHEach sequestering agent has an optimum pH range and it’s highly recommended to follow it.Reaction timeTime is needed to allow the chemical to work.Water ageSequestering agents are usually reliable for approximately 3 to 5 days depending on temperature.22
23. Chemical EffectivenessHardness (Calcium Ca2+ and Magnesium Mg2+)Moderately to high water hardness significantly limits the effectiveness of polyphosphates.Dosage control (normally 1-3 ppm) unless high hardnessConcentration of iron and manganese (when combined concentrations are above 1 ppm, sequestering not usually effective).23
24. Where to FeedSequestering Agent?24WellPolyphosphateChlorineMixerEP001DistributionPolyphosphateChlorine
25. Profile(Aeration and Filtration)251.Dissolved O2Total Fe & MnSoluble/Insoluble Fe & MnpHEP0014Distribution156AeratorFilter23WellChlorineSample Location2.Dissolved O2Total Fe & MnSoluble/Insoluble Fe & MnpHFCL3.Total Fe & MnSoluble/Insoluble Fe & MnFCL4-6.Total Fe & MnSoluble/Insoluble Fe & MnFCL
26. Profile (KMnO4 & Filtration)261.Total Fe & MnSoluble/Insoluble Fe & MnpHEP0014Distribution156Filter23WellSample Location2.Total Fe & MnSoluble/Insoluble Fe & MnpH3.Total Fe & MnSoluble/Insoluble Fe & Mn4-6.Total Fe & MnSoluble/Insoluble Fe & MnFCLKMnO4ChlorineNote: conduct drawdown test to determine dosage of KMnO4. Also, need well flow rate.
27. Profile Surface Water Treatment 27EP0012Distribution45Alum1KMnO4ClarifierFilters3Caustic1.Total Fe & MnSoluble/Insoluble Fe & MnpH2.Total Fe & MnSoluble/Insoluble Fe & MnpH3.Total Fe & MnSoluble/Insoluble Fe & MnpH4-6.Total Fe & MnSoluble/Insoluble Fe & MnTCLpHChlorineLAS
28. Manganese Interference with Chlorine Residual MeasurementsMatthew T. Alexander, P.E.Office of Ground Water and Drinking WaterStandards and Risk Management DivisionTechnical Support Center,Cincinnati, OH
29. DisclaimerThe information in this presentation has been reviewed and approved for public dissemination in accordance with U.S. Environmental Protection Agency (EPA). The views expressed in this presentation are those of the author(s) and do not necessarily represent the views or policies of the Agency. Any mention of trade names or commercial products does not constitute EPA endorsement or recommendation for use. U.S. Environmental Protection Agency29
30. OutlineWhy is Manganese a Concern?Case StudiesApproaches to Minimize Interference with Chlorine AnalysisU.S. Environmental Protection Agency30
31. Why is Manganese a Concern?In 2004, EPA issued a Drinking Water Health Advisory for manganese (Mn):A secondary maximum contaminant level (SMCL) of 0.050 mg/L based on aesthetic considerations;A chronic (lifetime) health advisory (HA) level of 0.3 mg/L;An acute 10-day HA value for infants younger than 6 months of 0.3 mg/L; and An acute 1-day and 10-day HA value for adults and children older than 6 months of 1.0 mg/L.Manganese was included in UCMR4, and a summary of occurrence data may be found here: https://www.epa.gov/sites/production/files/2018-10/documents/ucmr4-data-summary.pdfU.S. Environmental Protection Agency31
32. Why is Manganese a Concern?Manganese can exist in various oxidative states, where chemical and physical properties can vary substantially (e.g., solubility, color).Insoluble forms of manganese can result in aesthetic issues, even at concentrations below the SMCL, leading to customer complaints and lack of consumer confidence. Oxidized forms of manganese (Mn3+, Mn4+, Mn7+) are also positive interferences with N,N-diethyl-p-phenylenediamine (DPD) chlorine methods, which could result in biased high measurements of disinfectant residual.U.S. Environmental Protection Agency32
33. Interference with DPD Chlorine MethodsDPD chlorine methods are based on chemical redox (oxidation-reduction) reactions that form a pink color when chlorine or other oxidants react with DPD reagent in solution. The intensity of the color is a function of the total oxidizing capacity of the sample, which includes interferents such as:Other Disinfectants – chlorine dioxide, inorganic chloramines, ozone, bromine, hydrogen peroxideDisinfection Byproducts – chlorate, chlorite, bromate, and others?Organic Chloramines – formed when chlorine reacts with organic nitrogen compounds to form amines, amino acids, and other compoundsOxidized Metals – chromium (Cr6+), manganese (Mn+3 to Mn+7)U.S. Environmental Protection Agency33
34. Case Study #1 – Idaho GW SystemData from distribution system (DS) optimization workshop during Region 10 AWOP meetingChlorine data was difficult to interpretDS concentrations were greater than EP residual (≈ 1.0 mg/L) Residuals at some remote locations was unexplainably highIndophenol method was also used at a few locations (data not shown) and DPD method was up to 0.4 mg/L greater U.S. Environmental Protection Agency34DS Entry Point (EP)
35. Case Study #1 – Idaho GW SystemIdaho staff and water system conducted follow-up sampling based on workshop resultsMonitored manganese and free chlorine using both DPD and indophenol methodsAdditional data suggested that manganese could be interfering with DPD free chlorine measurementsU.S. Environmental Protection Agency35SiteTotal Mn(mg/L)DPD Free Cl2(mg/L)Indophenol Free Cl2(mg/L)Free Cl2 Method Difference(mg/L)Percent Difference (%)A0.2651.140.470.67143B0.2560.900.230.67291C1.540.600.150.45297D0.6921.240.320.92286
36. Case Study #2 – New Mexico GW SystemSystem triggered Level 1 Assessment under the Revised Total Coliform Rule.Abnormally high free chlorine residual was found in the DS during the Level 1 AssessmentMeasured residual from hydrant at remote DS location was ≈10x greater than EPFree chlorine measurements were higher at locations with discolored waterU.S. Environmental Protection Agency36Sample LocationAugust 21stAugust 22nd August 23rd Entry Point0.73-0.63Site #5-0.370.19TCR #0270.080.65-TCR #0090.010.11-Site #11-0.08Site #7-0.22Hydrant near end of DS6.96.6-Increasing Water AgeFree Chlorine Residual (mg/L) – DPD Method
37. Case Study #2Follow-up study was conducted a few weeks laterSystem conducted extensive flushing since prior site visit Compared free chlorine residual from DPD and indophenol methodsMeasured dissolved, suspended, and total MnData suggests that Mn was interfering with DPD measurementsIndophenol method suggests inadequate disinfection residual at EP and some DS locationsU.S. Environmental Protection Agency37Sample LocationSuspended Mn (mg/L)Dissolved Mn (mg/L)TotalMn (mg/L)DPD Total Cl2(mg/L)DPD Free Cl2(mg/L)Indophenol Free Cl2(mg/L)Raw0.040.840.88---Treated (EP)0.030.000.030.600.460.14Site #50.070.010.080.320.230.09TCR #0270.220.070.290.230.180.17TCR #0090.010.000.010.040.110.00Site #110.090.010.100.140.130.10Site #70.240.010.250.370.270.00Hydrant0.300.010.310.620.270.00Increasing Water Age
38. Approaches to Minimize Interference with Chlorine Analysis: Pre-Treat SampleInterference from manganese may be minimized by a blank correction (see S.M. 4500-Cl F1d):Sample is dechlorinated with sodium arsenite, which does not react with manganese. The dechlorinated sample is then analyzed using the DPD method procedure.The result from the dechlorinated sample (i.e., manganese interference) is then subtracted from the result of a non-dechlorinated sample.A step-by-step procedure to pre-treat a sample is also summarized in DPD chlorine method summaries provided by manufacturers (e.g., Hach Methods 8021 and 8167).Sample waste containing sodium arsenite must be disposed of in accordance with local, state, and federal regulations.U.S. Environmental Protection Agency38
39. Approaches to Minimize Interference with Chlorine Analysis: Use Indophenol MethodIndophenol free chlorine method was approved by EPA for the determination of free chlorine in drinking water in July 2016.Unlike DPD methods, indophenol chemistry is not susceptible to interference from manganese and many other compounds.Does not require sample pre-treatment with sodium arsenite and resulting hazardous waste.Relatively longer sample reaction time than DPD methods.U.S. Environmental Protection Agency39
40. SummaryIn addition to potential health issues associated with consuming elevated levels of manganese, it can indirectly cause other public health issues associated overquantifying disinfectant residual.Disinfectant residual may be accurately quantified in samples containing oxidized manganese by pre-treating samples or using an alternative method.Potential interferences should always be considered when measuring disinfectant residual (e.g., manganese, organic chloramines, other oxidants).U.S. Environmental Protection Agency40
41. Contact Info: 41Matthew Alexanderalexander.matthew@epa.gov513-569-7380