Chlorine Decay, Water Age, and THMs - OH MY - Ohiowater.org

Chlorine Decay, Water Age, and THMs – OH MYResidual Decay Models• Residual decay follows first order reactionCtCoekt• C t = concentration at time t• C o = initial concentration• k = residual decay coefficient• t = decay time in days• Calculate decay coefficients (k) using reaction equation• Excel graphing function works well• Decay models developed using identified coefficients forfree chlorine and monochloramine4

Chlorine Decay, Water Age, and THMs – OH MYResidual Decay Models• First order reactionCtCoekt• Calculate decay coefficient (k) using water age from zero days to xdays• Two day intervals• Can use shorter or longer intervals as needed• k values appear to be site specific• Temperature dependence of k - 2 fold change for each 10 o C changein temperature (adjust k accordingly)5

Chlorine Decay, Water Age, and THMs – OH MYResidual Decay Models• First order reactionCtCoekt• Calculate decay using average to maximum residual concentrations• May need to spike sample to a known concentration• Model data tabulated into spreadsheet• Graphical illustrations of model data predictions• Free chlorine decay much faster than monochloramine decay• Decay occurs due to organics, ammonia, iron, manganese6

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data Collection• Plant tap samples analyzed and held at room temperature• Residuals analyzed initially (day zero), then at simulated water agesof 1 day, 3 days, 5 days, etc.• Free chlorine• Monochloramine• Residual decay determined from lab data• Based on current plant operations and water quality• Calculations and graphical illustrations• Determination of decay coefficient (k)• Free chlorine• Monochloramine7

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data CollectionAverage Finished Water Quality - Plant AParameterConcentrationWater pH, s.u. 8.3Alkalinity, mg/L as CaCO 3 80TOC, mg/L 4.1UV absorbance, cm -1 0.058SUVA, L/mg-m 1.41THMFP, µg/L 252Chlorine demand, mg/L 2.148

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data CollectionFree ChlorineDecay CurvefromExperimentalData9

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data CollectionMonochloramineDecay CurvefromExperimentalData11

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data CollectionMonochloramineDecay CurvefromExperimentalData -CorrelatingTemperatureDependence12

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data CollectionAverage Finished Water Quality - Plant BParameterConcentrationWater pH, s.u. 8.5Alkalinity, mg/L as CaCO 3 56TOC, mg/L 1.2UV absorbance, cm -1 0.024SUVA, L/mg-m 1.90THMFP, µg/L 53Chlorine demand, mg/L 1.4213

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data CollectionFree ChlorineDecay CurvefromExperimentalData14

Chlorine Decay, Water Age, and THMs – OH MYLaboratory Data CollectionFree ChlorineDecay CurvefromExperimentalData -CorrelatingTemperatureDependence15

Chlorine Decay, Water Age, and THMs – OH MYModel Data versus System Data - Plant AFree ChlorineResidualsComputer ModelPredictionsActual SystemMonitoring2 day water age, mg/L 1.01 0.964 day water age, mg/L 0.56 0.536 day water age, mg/L 0.32 0.308 day water age, mg/L 0.20 0.2095.6% accuracyBased on average plant tap free chlorine residual 1.8 mg/L16

Chlorine Decay, Water Age, and THMs – OH MYHydraulic Modeling17

Chlorine Decay, Water Age, and THMs – OH MYHydraulic Modeling - Water Age• Hydraulic modeling based on system operations• Computerized map of distribution system• Pipe sizes and lengths• 6-inch and greater diameters typical• 4-inch and greater for small systems• Flow from plant through system• Software predicts flow patterns and water age• Some software can predict water quality changes• Water age map color coded corresponding to predictions• Low water age near treatment plant• High water age at extremities• Related to residual decay and DBP formation18

Chlorine Decay, Water Age, and THMs – OH MYHydraulic Modeling Water Age - Plant A4 days8 days4 days2 days2 days8 days2 daysWTP4 days6 days2 days4 days6 days4 days19

Chlorine Decay, Water Age, and THMs – OH MYHydraulic Modeling Water Age - Plant B8-10days6-8days6-8days10days20

Chlorine Decay, Water Age, and THMs – OH MYComparisons of Decay and Water Age• Distribution chlorine monitoring used to compare residualdecay and hydraulic models• Residual maintenance effective in much of the system• Maintenance difficulties at the system extremities• Decay data compares closely to predicted water age• Can be used for water age predictions• Believed to be accurate for establishing operating parameters basedon disinfection practices21

Chlorine Decay, Water Age, and THMs – OH MYDecay vs. Water Age - Plant A4 days8.5 days8 days4 days3.5 days4.5 days2 days2 days8 days2 days2 days2 days5.5 daysWTP7 days4 days6 days3.5 days2 days4 days6 days4 days22

Chlorine Decay, Water Age, and THMs – OH MYDecay vs. Water Age - Plant B8-10days6-8days11days7 days7 days6-8days3.5days10days23

Chlorine Decay, Water Age, and THMs – OH MYTHM Formation24

Chlorine Decay, Water Age, and THMs – OH MYTHM Formation Reaction0.44 0.409 0.2651.060.7150. 0358UV* TOC * Cl * RXN * TEMP * pH 2.6 *( Br 1TTHM, moles / L 0.00309*254 2)UV254 UVabsorbanceat254nanometers,cm1TOC Totalorganiccarbon,mg / LCl2 Chlorinedosage,mg / LRXN Coefficien trelatedtowaterageTEMP Watertemperature,oCpH Water pH,s.u.Br Bromide,mg / LFormation and Control of Disinfection Byproducts in Drinking WaterAWWA 199925

Chlorine Decay, Water Age, and THMs – OH MYTHM Formation Reaction• Strong formation dependence• Water temperature• Water pH• Organic content• Chlorine dosage• Weaker formation dependence• Water age or residence time• Bromide concentrationChloroform26

Chlorine Decay, Water Age, and THMs – OH MYTHM Formation Reaction• Parameters Under Operational Control• Water pH• Organic content• Chlorine dosage• Water age (storage and system residence)• Cannot be controlled• Water temperature• Bromide concentration27

Chlorine Decay, Water Age, and THMs – OH MYOrganic Contaminants in WaterAromatic CarbonMoleculesAromatic Carbon Ring Structure• Contain numerousdouble carbonbonds in a ringstructure• Double bonds andaromatic carbonsmeasured by UVA• Influence SUVAmake-up• Double bonds easilybroken – formdisinfectionbyproducts reactingwith halogens28

SUVA (L/mg-m)Chlorine Decay, Water Age, and THMs – OH MYOrganic Contaminants in Water8.07.57.06.56.05.55.04.54.03.53.02.52.01.51.00.50.0Transphilicacids (TPHA)Fulvic Acids(FA)Harder toRemove0 10 20 30 40% Aromatic CarbonHumic Acids(HA)Easier toRemove29

Chlorine Decay, Water Age, and THMs – OH MYImpacts from Disinfection TreatmentsChlorine• Chlorine dosage affects THM formation• Higher dosages lead to higher THMs• Increased dosage favors HAA5 formation over THM formation(dichloro- and trichloro- species, pH dependency)• Can result in NOM fractioning to TPHA and HPI• Can increase AOC byproductsHPC Bacteria Plate30

Chlorine Decay, Water Age, and THMs – OH MYTemperature/pH Effects• Formation reaction changes 2 fold each 10 o C change• Lower temp slows reaction rate• Higher temp speeds reaction rate• Summer conditions significantly increase THM levels• Affects NOM concentrations and precursor material• Lower temp reduces organic decay and NOM in source water• Higher temp increases NOM formation from organic decay31

Chlorine Decay, Water Age, and THMs – OH MYTemperature/pH Effects• pH dependence on THM formation• High pH favors THM formation over HAA5 formation• High pH increases THM formation reaction rate• High pH increases chloroform concentrations• High pH reduces HAA5 formation• Low pH opposite of above32

Chlorine Decay, Water Age, and THMs – OH MYBromide Effects on THM Reactions• Form DBPs 2 times faster than chlorine• Shifts from chlorinated to brominated species• Halogen substitution reactions like chlorine (Br - ion)• Attacks more NOM sites than chlorine• 50% bromide reacts to form THMs, where only 10% chlorine reacts toform THMs• Impact on THM concentration dependent on NOM concentration• Low NOM reduces bromide reactionBromoform33

Chlorine Decay, Water Age, and THMs – OH MYWater Age/Residence Time Impacts• Single most important factor in THM formation• 20% to 50% THMs form within treatment plant,remainder form in distribution system• THMs form fast in 1 st 48 hours, then reaction slowsexponentially• 70% to 95% HAA5s form within treatment plant• Long residence time increases THMs in storage tanksand piping• Can result in biodegradation of HAA5• Reduction in water age reduces THMs (flushing,looping mains, tank mixing, etc.)34

Chlorine Decay, Water Age, and THMs – OH MYTHM Treatment Control Methods• Oxidative conditioning• Strong oxidant application severs C=C bondsmaking TOC removal more effective• Avoid changing hydrophobic matter intohydrophilic matter• Coagulant precipitation and adsorption• Iron salts typically more effective than aluminumsalts• Dosage important to remove TOC• Alkalinity more important than pH for TOCremoval35

TOC Concentration, mg/LChlorine Decay, Water Age, and THMs – OH MYTHM Treatment Control Methods• Enhanced softening• Mg(OH) 2 acts as coagulant adsorbing TOC• Additional 10% to 30% TOC removal possible• Avoid saponification with high pH5.505.255.004.754.504.254.003.75High pHleads to poorremovals3.503.253.002.752.509.50 9.75 10.00 10.25 10.50 10.75 11.00 11.25 11.50 11.75 12.00Water pH, s.u.36

Chlorine Decay, Water Age, and THMs – OH MYTHM Treatment Control Methods• Biological Filtration• Sufficient oxidation to increase BDOC and AOC• Ozone most common, but other strong oxidants can beused• Conventional treatment can result in biological TOCreduction in filters• 6% to 14% observed in full-scale operations• GAC substrate used to grow TOC reducing bacteria37

Chlorine Decay, Water Age, and THMs – OH MYTHM Treatment Control Methods• GAC Contactors• EBCT most important parameter• 20 minutes most effective• 10 minutes effective with more frequent GACreplacement• TOC breakthrough dependent on make-up of NOMand concentration applied• 30 days to 350 days provided in many WTPs38

Chlorine Decay, Water Age, and THMs – OH MYTHM Treatment Control Methods• Anion Exchange Treatment• Strong base anion (SBA) resins remove TOC• Several manufacturers and exchange capacitiesavailable• Macroporous resins have longer life• Gel type resins capture smaller molecularweight NOM• Relatively high bed volume throughputbetween regenerations• Typical TOC removal 55% to 95%• TOC breakthrough and pH increase generallysignal regenerationAnion ExchangeReactors39

Chlorine Decay, Water Age, and THMs – OH MYTHM Treatment Control Methods• Membranes• NF or RO membranes provide TOCremoval• Dependent on MWCO (

Chlorine Decay, Water Age, and THMs – OH MYTHM Treatment Control Methods• Tank Aeration/Mixing• Stripping of volatile THM compounds withaeration in storage tanks• Chloroform most common form removed, butcan reduce other THM species• Ventilation of air space above water important• Mixing helps reduce stagnant water zones• Improved residual maintenance• Air-to-water ratio important to produceTHM stripping without depleting chlorineresidual41

Chlorine Decay, Water Age, and THMs – OH MYTank Turnover vs. Water Age• Tank Turnover• Fluctuating water levels daily• 15% to 60% turnover is common• Theoretically reduces water age in storage• Actually does not reduce stagnant zones orresidual decay• Stagnant zone rides up and down with waterlevel• System flushing likely best practice toremove stagnant water from the system• From plant outwards to the system extremities• Durations determined by residuals producedafter flushing42

Chlorine Decay, Water Age, and THMs – OH MYSummary• Computer models can be useful for establishing operatingtargets• Hydraulic modeling can be useful for predicting water age• Residual decay modeling can predict water age close to hydraulicmodels and can predict residuals in the system• THM formation is a function of many parameters thatcannot be totally controlled• Reducing organics, managing pH, and controlling water age are bestpractices for lowering THM formation– Reduces residual decay that results in higher THMs– Reducing water age by flushing and storage levels reduces THM formation• Tank mixing and aeration helps remove THMs that form in the system43

Chlorine Decay, Water Age, and THMs – OH MYMarvin Gnagymcg7@bex.net419.450.293144