Impact of EPA Drinking Water Stage 2 Disinfectant and Disinfectant ...

1Impact of EPA Drinking Water Stage 2Disinfectant and Disinfectant By-ProductRuleNCAWWA-WEA 2013 Spring ConferenceApril 15, 2013Eric JordanRegional Sales ManagerSwan Analytical USADisinfection

2Agenda• Regulations– Safe Drinking Water Act• Disinfection– Monochloramine• Disinfection By-Products• Measuring Disinfectant Concentration• Desirable Analyzer Features• Conclusion• QuestionsDisinfection

3Safe Drinking Water Act of 1974• The Safe Drinking Water Act (SDWA) is themain federal law that ensures the quality ofAmericans' drinking water.• Under SDWA, EPA sets standards for drinkingwater quality and oversees the states, localities,and water suppliers who implement thosestandards.• The law was amended in 1986 & 1996 requiringmany actions to protect drinking water and itssources: rivers, lakes, reservoirs, springs, andground water wells.Disinfection

Amendments to Safe Drinking Water Act of 19744• Amendments to the SDWA in 1996 requireEPA to develop rules to balance the risksbetween microbial pathogens and disinfectionbyproducts (DBPs).• The Stage 1 Disinfectants and DisinfectionByproducts Rule and Interim Enhanced SurfaceWater Treatment Rule, promulgated inDecember 1998, were the first phase in arulemaking strategy required by Congress aspart of the 1996 Amendments to the SafeDrinking Water Act.Disinfection

Stage 2 Rule5• The Stage 2 Disinfectants and DisinfectionByproducts Rule (Stage 2 DBPR) builds upon theStage 1 DBPR to address higher risk public watersystems.• This final rule strengthens public health protectionby tightening compliance monitoring requirementsfor two groups of DBPs, trihalomethanes (TTHM)and haloacetic acids (HAA5).• Stage 2 DBPR requires systems to perform asystem evaluation to identify the locations withhigh DBP’s which become the systemscompliance sampling points.Disinfection

6Why Disinfection?Disinfection

Chemistry of Chlorination7• Free chlorine is a powerful oxidant and reactsrapidly with organic and inorganic matter.• As a result, the strong disinfectant residual itinitially provides may not persist as long asnecessary within the distribution system.• Free chlorine can readily react with organics toform unwanted disinfection byproducts (DPBs)such as trihalomethanes (THMs) and haloaceticacids (HAAs).Disinfection

8Chemistry of Chlorination• How does chlorine actually carry out disinfection?• Depending on pH, the reaction of HOCl and water furtheryields an equilibrium between hypochlorous acid andhypochlorite ion.• The further dissociation, along with the two types of“hypos”(mainly hypochlorous acid which is electricallyneutral), can penetrate the cell walls of the organism anddisplace molecules needed to survive. The organism can nolonger function or replicate and eventually dies.Disinfection

9Chemistry of Chlorination• Free Chlorine• HOCl is approx. 70-90 timesstronger oxidant then theHypochlorite ion “OCl-”which is predominant inhigher pHs.• Efficiency of Disinfectionwith Free Chlorinedecreases significantly withan increase in pH value.Disinfection

10Chemistry of Chlorination• Chlorine, an element in the halogen family, isrepresented by the symbol Cl. It has oneunpaired electron in its outer valence shellmaking it highly reactive and an oxidizing agent.unpairedelectronDisinfection

11Chemistry of Chlorine• Atomic Number 17, 17 positively charged protons in the nucleuswhich are neutralized by the 17 negatively charged electrons in aseries of outer shells• These shells, which applies to most every atom in the periodic table,will be full and stable at 8 electrons.(Octet Rule)(Noble Gases)• Chlorine is in group 7 in the periodic table which means it has 7electrons in its outer shell which are used in bonding.• If chlorine were to lose these 7 electrons, then the 7 protons in thenucleus would be in excess giving chlorine a valence(oxidation state)of +7.• This is not how it works, chlorine by definition(Octet Rule) wants tohave a full outer shell(8e’s) so it takes on one electron to have anoverall valence of -1. Thus giving a stable chlorine radical of Cl -1• Chemistry is the constant attraction and repelling of electrons. Theforces that cause bonding are simply just electrons combining withother electrons.Disinfection

Chemistry of Chlorination12• Elemental chlorine exists as a two-atom moleculewith the symbol Cl 2 . In this arrangement, eachatom has 8 valence electrons in its outer shell.• The molecular weight of thisdiatomic molecule is 70.92.• The bonding between the two atoms is relativelyweak and keeps the Cl 2 molecule highly reactive.Disinfection

13Chemistry of Chlorination• During hydrolysis, chlorine reacts rapidly withwater to form hypochlorous acid (HOCl) andhydrochloric acid (HCl).Cl 2 + H 2 OHOCl + HCl• Of the two compounds, hypochlorous acid ismore important in the water treatment process. Itcontains the active form of chlorine that will beused to disinfect organisms.Disinfection

14Chemistry of Ammonia• Ammonia (NH 3 )is acompound made up ofone nitrogen atom andthree hydrogen atoms.• The nitrogen atom hasan atomic mass of 14and each hydrogenatom has an atomicmass of 1 givingammonia a totalmolecular weight of 17.Disinfection

15History of Monochloramine Use• In the early 1900’s chloramination receivedattention when it was found that the cost ofchlorination might be reduced.• The practice of monochloramine treatment wasadopted in 1916 in Ottawa, Ont.• The first installation in the United States was in1917 in Denver, Colo. Both locations usedammonia and hypochlorite and notedimprovements in taste .• Becoming more popular to mitigate unwanteddisinfection by-products (DBPs).Disinfection

Chemistry of Chloramines16• Chloramines are less aggressive disinfectantsthat reacts more slowly than chlorine howeverremains longer in the distribution system.• Given more stringent disinfection byproductregulations, chloramination can be an appealingalternative to the use of free chlorine as a meansof limiting DBP formation – particularly THMs.• Additional benefits are fewer taste and odorconcerns are reported by consumers ofchloraminated water.Disinfection

17Chemistry of ChloraminesThe Basics:Hydrogen1H 114N 735.4Cl 17NitrogenChlorineDisinfection

18Chemistry of Chloramines• Chloramine is a general term that describes threerelated compounds:• Monochloramine, NH 2 Cl• Dichloramine, NHCl 2• Trichloramine, NCl 3• Monochloramine is the preferred chloraminecompound for drinking water disinfection.Disinfection

19Chemistry of Chloramines• The molecular structure ofall three chloraminecompounds resembles thestructure of ammonia.• A chlorine atom willreplace one, two, andthree hydrogen atomsrespectively for theformation of mono-, di-,and trichloramines.NH 3 + HOCl à NH 2 Cl + H 2 ONH 2 Cl + HOCl à NHCl 2 + H 2 ONHCl 2 + HOCl à NCl 3 + H 2 ODisinfection

20Chemistry of Chloramination• The formation of di-and tri-chloramine isminimized by adding a specific weight ratio ofchlorine and ammonia to water while maintainingthe optimal pH range.• Di-and tri-chloramines can contribute anobjectionable taste and odor to the treated water.• Monochloramines are effective biocides thatcontribute least to taste and odor problems.Disinfection

21CleanWaterDBP: Free Chlorine TreatmentChlorinationFree ChlorineFew if anyChloraminesFreeChlorineTotalChlorineDBP0.50ppm 0.55ppm 0.05ppmNSCWaterChlorinationFree ChlorineChloraminesformingFreeChlorineTotalChlorineDBP0.35ppm 0.55ppm 0.20ppmNSC: Not So CleanIncreasing DBP values will raise alarmsand the source can be investigated.Disinfection

22DBP: MonochloramineChlorinationAmmonia additionTreatedWaterMainlyFree ChlorineMainly Monochloramine.Some byproducts mightbe formedDistributionFreeChlorineFree ChlorineBefore Ammonia additionMonochloramineTotalChlorineDBP0.05ppm 1.00ppm 1.1ppm 0.05ppmFree ChlorineMonochloramineDisinfection byproductsIncreasing DBP values will raise alarmsand the source can be investigated.Disinfection

Chloramination Process23• To form the monochloramine compound, theappropriate weight ratio of chlorine and ammoniamust be determined and then properly managed.• Free ammonia entering the distribution systemmust be controlled to reduce the potential fornitrification.• Chloramines are weaker oxidizing agents,therefore a higher disinfectant residual is requiredfor similar results. A chloramine residual of 2.0mg/L is comparable to a free chlorine residual of0.5 mg/L.Disinfection

Chloramination Process24• All of the free chlorine will be converted tomonochloramine when the pH is between 6.5 and8.5 and the ratio of chlorine to ammonia isequimolar, 5:1 by weight or less. Since thisreaction is pH sensitive, the rate of reaction isimportant.• Reaction rates for 99% conversion of freechlorine to monochloramine at 25 Degrees C.pH 2 4 7 8.3Seconds 421 147 0.2 0.009– This is why optimum pH is 6.5 to 8.5Disinfection

Chloramination Process25• Chlorine atoms occur in pairs and have acombined weight of just over 70 atomic massunits.• The weight of ammonia is measured as N (whichis why it is often expressed as NH 3 -N), andnitrogen has an atomic mass of 14.• The difference between the weight of chlorineand ammonia (70 / 14 = 5) establishes thechlorine to ammonia weight ratio of 5:1.Disinfection

Chloramination Process26• Dosing chlorine and ammonia based on theweight ratio of 5:1 means that the requiredchlorine dose will be five times greater than theammonia dose.• For example, a target chloramine dose of 3.0 mg/L will require the addition of 3.0 mg/L of chlorineand 0.60 mg/L of ammonia to keep the 5:1 ratio.• The amount of each chemical to add depends onchemical strength and weight of treated water.Disinfection

27Chemical AdditionChemicalFeed Ratelbs./dayDosemg/L= X XMGD8.34lbs./galChemical Strength (decimal %)• The chemical feed rate equation above is used todetermine the amount of chlorine and ammoniato add. Examples showing different chemicalstrength feed requires follow.Disinfection

Chemical Addition28• Goal: 5:1 weight ratio to producemonochloramines• Target chloramine residual: 3.0 mg/L• Requires dosing: 3.0 mg/L Cl 2 and 0.60 mg/L NH 3• Daily production: 10 MG• Weight of water: 8.34 lbs./gal• Chlorine: 100% strength gas• Ammonia: 100% strength gas• Add 250 lbs. of chlorine and 62 lbs. ofammonia to produce the target results.Disinfection

29Chemical Addition• Goal: 5:1 weight ratio to producemonochloramines• Target chloramine residual: 3.0 mg/L• Requires dosing: 3.0 mg/L Cl 2 and 0.60 mg/L NH 3• Daily production: 10 MG• Weight of water: 8.34 lbs./gal• Chlorine: 12% strength sodium hypochlorite• Ammonia: 19% strength ammonium hydroxide• Add 1984 lbs. of chlorine and 318 lbs. ofammonia to produce the target results.Disinfection

30Measurement of Disinfectants• Precise and accurate measurement of the usedprimary disinfectant and their byproducts is anincreasing concern.• As the disinfection strength depends on pH itmust be measured.• Correct measuring equipment for the disinfectantis fundamental for the process and allowscorrect dosing with less chemicals DBPs.Disinfection

31Measurement ChallengesPhotometry, sensor, or ?That depends on the water, measurementsrequired, and potential for fouling.Disinfection

32Measuring Chlorine Residual• What is required to make a continuousmeasurement reliable?• Three things!Provide valid readingsQuick verificationEasy & minimalMaintenanceDisinfection

33Desired Analyzer Design FeaturesProvide valid readings• Choice of a reliable and stable measurementprinciple• All readings from one analyzer• Critical influences must be monitored:— Membrane fouling cannot be monitored— KI availability in a membrane coveredsensor cannot be monitored.Disinfection

34Desired Analyzer Design FeaturesProvide valid readingsCritical influences for measurement:– Constant sample flow– Reagent availability– Optical system (photometer) functionalA continuous system must observe thesecritical parameters and inform the operator offailures.Disinfection

35Desired Analyzer Design FeaturesQuick verificationSubject to reliable quality checks at anappropriate frequency;• A continuous measuring system must haveprocedures implemented for verification.• Should not interfere with the measuring process(analyzer must not be offline for hours)Disinfection

36Desired Analyzer Design FeaturesEasy maintenanceMaintained and operated to a demonstrably highstandard at all times;• Maintenance-free analyzer does not exist!• Maintenance must be possible without usingspecial tools and easy to perform.• Parts should be easily accessibleDisinfection

37Summary of Desired FeaturesA continuous photometer system with DPD thatmeasures free chlorine, monochloramine, and totalchlorine:– Provides reliable reading for the primary disinfectant.– Provides reliable reading for monochloramineproduction and process control.– Provides accurate information about DBP pre-cursorforming or process problems– Informs the operators about validity of his result– Eliminates need for multiple analyzersDisinfection

38Measurement of Disinfectants• Free Residual Chlorine– Red color formation with DPD and buffer– Reaction time of 3 – 5 sec– According ISO 7393-2 / EPA 334.0– Other methods are acceptable (i.e. amperometric principle) aslong as they are calibrated against above mentioned DPDmethod.• Total Chlorine 1– Additional Potassium Iodide (KI) is added to the buffer.– Red color formation with DPD– Reaction time of 3-5 sec• Total Chlorine 2– Red color formation with DPD, buffer and KI– Reaction time of 120 seconds!Disinfection

39Measuring Process1. Zero measurement: Measurement of sample backgroundto compensate for light absorption effects (turbidity, samplecolor) not related to red DPD color2. Free residual chlorine (FRC) measurementSample + Buffer+DPD dosing, immediate reaction3. Total Residual chlorine 1 (TC 1) measurementSample + Buffer+DPD+KI dosing, immediate reaction-> Calculation of monochloramine content4. Total Residual chlorine 2 (TC 2) measurement:Sample + Buffer+DPD+KI plus 2 minutes to completereaction->Calculations:Combined Chlorine contentDisinfection

40Measuring Process1. Zero measurement2. Free residual chlorine (FRC)Measurement3. Total Residual chlorine 1 (TC 1)-> Calculation of Monochloramine4. Total Residual chlorine 2 (TC 2)-> Calculation of Combined Chlorine-> Calculation of Dichloramine5. Flush (4 minutes)2 minDisinfection

Monochloramine Monitoring41• Chlorine-Ammonia Treatment– NH 3 is added to the chlorinated water to formmonochloramines:HOCl + NH 4 OH à NH 2 Cl + 2 H 2 O– Excess of NH 3 will consume all Free Chlorine andcontaminates the water– Too little NH 3 means too much Free Chlorine is left,which will react with NH 3 to form unwantedDichloramines and other byproducts.– An ammonia monitor can also be employed tomonitor and control ammonia.Disinfection

Monochloramine Monitoring42• How can the a well designed analyzer support waterutilities in optimizing their disinfection process?– Measures Free Residual Chlorine (FRC), Total Chlorine 1(TC1), Total Chlorine 2 (TC2)– Calculate monochloramine (CMC, true monochloramine),Di-/ Tri-chloramines (CDC), Combined Chlorine (CCC)– Keep a minimum Free Chlorine (0.05 ppm) to avoidAmmonia overdosing– TC 2 should be equal [FRC & CMC] value, then theammonia has finished the conversion– If TC 2 is higher then [FRC&CMC], the difference is otherchloramines forms, indicating an overdose of Chlorine– Ammonia measurement or other additional instrumentsare not necessary but available if desiredDisinfection

Would You Benefit?43• Would you benefit from a single analyzer thatmonitors– Free chlorine– Total chlorine– Combined chlorine (chloramines)• If using monochloramine would you benefit froma single analyzer that measures– Free chlorine– Monochloramine– Total chlorine– Combined chlorine (chloramines)• Would you be interested in such an analyzer?Disinfection

Free, Monochloramine, & Total Chlorine All in One44• The AMI Codes II CC monitorsreliably all relevant values for thedisinfection process and byproductforming.• The operator is informed aboutmeasurement validity.• The integrity of the analyzer can beverified within minutes.Disinfection

45Questions?Thank you for your attentionDisinfection