Presentation on theme: "Review of the Production and Control of Disinfection By-Products (DBP’s) In this section we will describe the constituents that form DBP, how these constituents."— Presentation transcript:
1 Review of the Production and Control of Disinfection By-Products (DBP’s) In this section we will describe the constituents that form DBP, how these constituents combine in a water treatment system, the mechanisms that are important in controlling them and qualitative and quantitative approaches in isolating and reducing DBPs when they are formed.
2 Goals of DBP Review Review Disinfection By-Product MCL’s Review How DBPs are FormedReview Water Sources and ID Conditions that Contribute to a DBP ProblemIdentify Measuring Parameters Associated with NOM and TOCIdentify DBP Best Management PracticesReview DBP Troubleshooting GuideConduct Interactive Role Playing Exercise
3 DEP MCL Requirements for DBP’s TTHM, HAA5, Chlorite and Bromate TTHM mg/lHAA mg/lChlorite mg/l*Bromate mg/l *** associated with the use of Chlorine Dioxide** naturally occurring precursor in systems near saltwater, associated with use of OzoneThe Safe Drinking Water Act regulates Total Trihalomethanes and Haloacetic Acids with specific MCLs. Also regulated are by-products from chlorine dioxide (chlorite) and Ozone (Bromate) use. Bromate is produced by a reaction between naturally occurring bromide in surface water and ozone. Bromide concentrations are higher if there is a saltwater intrusion source.
4 Disinfection Byproducts Formation NOM + Cl THMs + HAAs + Other DBP CompoundsDisinfection Byproducts (DBP) are produced by the reaction of free chlorine with natural organic material (NOM) found in source waters.The amount of organic materials (NOM) can be approximated by the amount of Total Organic Carbon (TOC) present.The portion of the NOM that forms the DBP’s is generally the dissolved portion (DOC is that part of the TOC that can be identified by first removing the NOM that is retained on a 45 micron filter)Disinfectants (such as chlorine) are used to protect public health. They attack, deactivate and kill all sorts of microorganisms that could threaten water consumer health. Disinfection is a major factor in reducing health risks from pathogens, however, disinfection is a double-edged sword. Disinfectants themselves can react with naturally occurring organic materials in water to form unintended organic by-products which pose health risks.When free chlorine is added to source waters containing natural organic material (NOM) chemical reactions will occur, which produce Disinfection Byproducts (DBP). NOM is the precursors of Disinfection Byproduct (DBP) formation. NOM in source waters are generally naturally occurring organic substances, such as humic and fulvic acids. These acids belong to a family of compounds having similar structure and chemical properties and are formed during the decomposition of vegetation.
5 Sources of Natural Organic Material (NOM) in Surface Water Rain Events wash organic matter into receiving body.Flooding reverses flow gradients in upper aquifersCavities and Fissures in Karst Conditions allow surface intrusionPoor Sanitary Conditions, i.e., broken seals, abandoned wells, poor locations, result in intrusionGround Water that has high NOM content is indicative of the intrusion from Surface WaterSedimentation, biogrowth or poor flushing practices in distribution systems increase organics concentration.Natural Organic Matter makes up the humic content in source waters. NOM is either hydrophilic (more soluble in water) or hydrophobic (less soluble and a more aromatic fraction.) Hydrophobic matter is easier to remove in the treatment process.
6 Use of Different Carbon Surrogates NOM SpeciesDescriptionSignificanceTOCTotal amount of all forms of Organic Carbon PresentGood overall indicator of potential DBP problemsDOCThe TOC passing through a 0.45 micron filter is dissolvedBetter indicator of the reactive portion of the TOCUV254Used to identify light absorption of reactive humic componentsIdentifies the reactive potion of the DOCSUVARatio of UV254 to DOCBest indicator of reactive portion of the TOC
7 Raw Water Considerations DBP Problem analysis always starts with a well investigation!Generally surface waters or ground waters under the direct influence of surface water (UDI) will have higher levels of organic materials (TOC.)Surface waters have higher treatable humic content than GWIf Surface water mixes with ground water, each well may experience different levels of TOCs.The humic content can be approximated by using SUVA.Because organic material in the water is a natural process of plant decay, surface waters will have a higher contents of NOM than ground waters. About 90% of the TOC concentration in a water supply is dissolved. For this reason TOC is a good surrogate for measuring the waters organic content.In many instances groundwater sources obtained from wells may also contain high levels of organic constituents from surface water interconnections. If the treatment plant is using a blended source from several wells, the individual wells, even if located relatively close together, can have very different organic contaminant characteristics.The type of organic content in the water will influence how the water is treated. A further refinement of the TOC analysis used to determine effective treatment is the SUVA test. SUVA stands for Specific Ultraviolet Absorption. The test uses UV radiation which when absorbed at a specific wavelength is proportional to the humic organic concentration of the water. SUVA is used to determine if enhanced coagulation is appropriate.
8 Organic Carbon (TOC) or Precursors in Natural Waters mg/l Mean Surface Water 3.5Sea WaterGround WaterSurface WaterSwampWastewaterWastewater Effluent
9 Typical Values of TOC for Various Waters Type of WaterRange in mg C/lSea Water0.5 – 5.0Most Ground Water0.1 – 5.0Surface Water1.0 – 20Swamp Water75 – 300Effluents Biotreatment8.0 – 20Wastewater50 – 1000WMDInter-MediateMedianFloridanMedianmg C/lNWFWMD6.1<1.0SRWMD2.0SJRWMD5.53.3SWFWMD9.816.8SFWMD6.31.9STATE4.82.2Kavanaugh published these representative values for various waters in a paper published in the AWWA Journal. What can be identified from the chart is that ground waters are significantly lower in TOC than surface waters. Thus groundwater treatment plants that are influenced by surface waters will exhibit a higher level of TOC.
10 Thickness and Extent of Intermediate Aquifer Confinement The Confining Unit restricts flow of groundwater between the Surficial Aquifer and Floridan Aquifer when present.Protects underlying Floridan Aquifer, Florida’s primary source of drinking water, from potential contaminationIn this map the lack of intermediate (Hawthorn) confinement is most visible in the Western part of North Florida generally following Interstate 75.In areas where confinement is absent surface water impacts are of greater concern since they will be immediate.N
11 Karst Features N Light areas indicate Karst features Karst is a type of topography that is characterized by depressions caused by the dissolution of limestone.These features include caves, sinkholes, springs, and other openings.In karst areas, interactions between surface water and groundwater are extensive and groundwater quality can degrade quickly.NAlthough confinement is protecting the Upper Floridan from the effects of surface water contamination, Karst features are much more prevalent and can provide direct conduits in areas of water withdrawal for the introduction of contaminants.Light areas indicate Karst features
12 Reducing the Production of Disinfection By-Products Eliminating Sources of Surface Water into Production WellsSelecting Well Blends with Lower DBPsRemoving Precursor Material within treatment processChanging the Point(s) of Chlorine ApplicationLowering the Chlorine Dose and/or ResidualUsing Alternate Disinfection StrategiesEnsuring the WTP processes are absent of organic growth (ie. Ion Exchange and Activated Carbon Systems)Ensuring Water Tank TurnoverReducing Distribution System Water AgeFlushing water in slow moving areas and at dead-endsRemoving sediment that creates chlorine demandRemoving biofilm that converts inorganic to organic materialsThere are four methods for controlling disinfection by-products. These methods are ranked according to their effectiveness starting with those things that the operator should consider first.
13 Coagulation to Remove TOC TOC Removal using Enhanced Coagulation for Surface Water Plants (TT)TOC Alkalinity (CaCO3)Mg C/L >1202.0 to % % %4.0 to % % %> % % %Florida Source WatersThis slide shows the amount of TOC that can be removed for different TOC and alkalinity concentrations in a raw water using enhanced coagulation. While conventional coagulation jar testing is concerned with removal of colloidal materials. enhanced coagulation is used to determine the amount of coagulant that is most effective for TOC removal.Typically Alum is used and requires sedimentation/filtration Lime can also be used but has less ability due to high pH
14 Other Means to Remove TOC PermanganateLong Used for Taste and OdorRemoves color forming substances which are the same constituents that cause DBP formationRange of dosage vary on water quality with .25 mg/l to 20 mg/l.Average dosage is 2 to 4 mg/l with 30% TOC removal efficiencies reportedLimitation is that can not be used in systems with High Sulfide Levels or with changing conditionsActivated Carbon FilterWith Source Water TOC from 2 to 4 mg C/L Activated Carbon Systems typically remove >50%Activated Carbon comes in two forms:Powdered Activated Carbon (PAC)Granular Activated Carbon (GAC)Removal mechanisms are the same
15 Factors Affecting Disinfection By-Product Production w/ Cl2 Turbidity and the type of NOM presentConcentration of Chlorine added and how well it is mixedBromide Ion ConcentrationPresence of H2S, Iron and NH3Age of Water System (amt of CI pipeline)Warmer TemperaturesLonger Contact Times (MRT)Presence of Sediment in TanksIn surface waters as the turbidity increase so does the concentration of organic material or TOC. The TOC concentration is the largest driver of the formation of DBP. This is why it is so important to remove TOC prior to the addition of disinfectant.The concentration of chlorine will also influence the reactions.Higher pHs affect the development of DBPs. For this reason softening plants operating at high pH levels. will have a higher DBP formation potential than a plant using conventional coagulation treatment for the same source water.Higher temperatures result in higher potential for DBP. This is very important in surface water plants because as the temperature of the source water increases more algae is produced raising the potential for more TOC in the raw water.Longer contact times between the chlorine and the organic material will produce more DBP.
16 Breakpoint Chlorination Curve Oxidation/Reduction OnlyDBPs RemainDBP ProductionChloraminesThe breakpoint chlorination curve is shown to illustrate the progression of chlorine reactions that occur when chlorine is added to water containing contaminants. The X axis illustrates chlorine being added to a fixed quantity of contaminated water. The Y axis illustrates the measured chlorine residual concentration of chlorine available.Not that at point 1 no residual chlorine is available. As the chlorine is added inorganic contaminants in the water combine with the chlorine until they have all been reduced at shown at point 2. As chlorine is continued to be added it is reacting with organic materials present in the water. At point 3 all ammonia and organic material has been combined and we see the combined “chlorine residual” at point 3.As more chlorine is added it breaks down the chloramines and some chlororganics releasing ammonia. Not all chlororganics are broken down and some are the regulated DBP compounds that we are concerned with.When all the reactive combined chlorine compounds are destroyed, we have reached “breakpoint chlorination.” At this point we will have “free available chlorine.”To prevent the formation of disinfection by-products ammonia can be added to the water prior to chlorine addition to produce chloramine. Chloramine prevents additional chlororganics including DPBs from forming. This process is often used in water treatment and is called “chloramination.”Breakpoint Chlorination Curve
17 Steps in the Formation of DBPs with Free Chlorine Inorganic reducing constituents such as H2S, Fe & Mn and NH3 compounds react first (oxidation reduction reaction).When Iron, Sulfide or NH3 are present, they exert the major Chlorine DemandIron concentrations are required in the Secondary Standard submittal but Sulfide or NH3 are not.If there are products of Biological Metabolism such as Nitrite this will also react. (Important in Nitrification)Any readily soluble Organic Materials in the water (TOC) will then react forming DBPs.Further Free Chlorine addition will not destroy DBPs.Disinfection “jar test” can be used to identify reducing constituents but will not identify by specific constituent.The production of disinfection byproducts is well understood. In fact there are over 500 disinfection byproducts that have been identified to date. Currently EPA regulates only 4 THMs and 5 HAAs. There are many substances that cause chlorine demand. These substances can substantially reduce the amount of available chlorine available for disinfection.In a typical treatment plant, 30 minutes of chlorine contact time is required for optimal disinfection with good mixing. However, water supply treatment dosages must be established on the basis of maintaining a residual concentration of chlorine in the treated water. For this reason excess additional chlorine is often added to ensure a 0.20 PPM residual in all parts of the distribution system. This requires higher doses of chlorine at the plant which then causes the production of DBPs within the water distribution system.
18 Example of Calculating CL2 Demand Water Qualityactual mg/lCL2 MultiplierTotal CL2DemandFe = 0.30.64*0.19Mn = 0.061.30.07H2S = 0.22.1*0.42NO2 = 0.150.50NH3 = 0.110 to 121.20Org-N = 0.0510.05TOC = 1.00.10.10Chlorine Demand2.53* Note: Actual amount of oxidant must be about 15% – 20% higher
20 DEP Iron Treatment Requirements State Secondary Standards require Iron to be < 0.30 mg/l in the finished waterThus water systems with iron concentration greater than 0.3 mg/l would need to install filtersIron may be sequestered up to a concentration of 1.0 mg/lIn an aeration system Iron is removed by raising the pH while H2S is removed better at lower pH’s
21 Treatment Issues with Sulfide and Iron in Unlined CI Pipes > 0.3 mg/l Problematic because of colloidal solidsSulfide is remove by lowering pH and filteringUnreacted Sulfide will form “blackwater” with unlined CI pipesSulfate and Colloidal Sulfur can be reconverted to sulfide by bacteria in water tanks causing odorIron is removed by raising pH and filtering source waterUnfiltered Iron will result in “red water” complaintsIron can also be a corrosion product from unlined CI pipesIron will result in staining
22 Chlorine Disinfecting Power and pH Considerations in Water Chlorine reacts with waterProducing hypochlorous acid (HOCl) and the hypochlorite ion (OCl-)Chlorine is more reactive at lower pHs.Low pH forms > HAA5s, High pH forms > TTHMsWhen chlorine is added to water it combines with the water to form hydrochloric and hypochlorous acid. The hypochlorous acid (HOCl) is a weak acid and ionizes into the hypochlorite ion (OCl-) and the Hydrogen (H+) ion.The hypochlorous acid and the hypochlorite ion provide the disinfecting power of chlorine. The presence of each component HOCl and OCl- are dependant on the pH of the water. The lower the pH the more HOCl will be present and the stronger the disinfection power. The importance of this phenomenon is that as the pH rises less chlorine residual is needed to provide pathogen killing power.Old Hypochlorite contributes to DBP formation because doses must be higher!Hypochlorite (pH 12.5) raises pH at high dose levels!%HOCL%OCL-pH
23 Sources of Chlorine and Bromine in DBP Compounds Free ChlorineImproper NH3 applicationPoor Chemical MixingChloramine BreakdownBromineBromide from Saltwater or Brackish Water IntrusionDrought ConditionsPresence of Free ChlorineThe production of THMs by the addition of chlorine to water containing TOC is well understood. In the case of chloramine, THMs can be produced if the chlorine is added prior to the ammonia, if the mixing process is inefficient or if the chloramine has a long retention time in the water. Monochloramine will slowly hydrolyze releasing free chlorine. The DBP production capability of Chloramine is 5 to 35%.Bromide is found in higher concentrations in salt or brackish water. Intrusions from these sources will result in higher levels of bromide which in the presence of strong oxidants will breakdown into compounds that react similar to free chlorine and are more reactive. Drought conditions typically result in higher levels of salts in surface waters and in pulling water from deeper groundwater zones that contain higher levels of TDS. Bromide concentrations in these instances will be higher. The presence of free chlorine in the distribution system will continue to react with Bromide producing more bromine oxidants.
24 Effect of the Addition of Free CL at MCL+ Level with TOC Note that TTHM growth is directly proportional to the excess amount of chlorine present (in concentrations above 1 mg/l) and the excess TOC that is available for reaction.This relationship is steady as Cl residuals approach 1.5 mg/l.Note the 300% increase in the amount of TTHM made when chlorine and TOC are increased by 50%.CL at 4.3 PPMNumerous studies have been conducted that illustrate the reaction of chlorine with organic material. Here we can see that the formation of TTHM rises significantly with high dosages of free chlorine applied to water with concentrations of TOC that are typically found. Note to that the formation of HAA5 does note increase at the same rate ant that at normally found concentrations the HAA5 concentration has already leveled off.Florida Source Water often apporach 4 mg/l TOC
25 Chlorine Detention Time Small System Ave DemandTime Paced ControlWater Systems experience both Seasonal and Diurnal Demand Changes.Colder months require less chlorine dose.Wet and hot periods cause longer detention periods.In times when demand exceeds average demand, a time-paced Cl feed system overfeeds chlorine.Flow Paced Control
26 Production of Total Trihalomethanes (TTHMs) Trihalomethanes (TTHMS) are produced by the reaction of chlorine with organic constituents found in natural waters.The 4 Trihalomethane compounds of concern are:Chloroform (typically >70% inland) BromodichloromethaneBromoform (can be >70% coastal) DibromochloromethaneThe sum of the concentrations of these four compounds are Total Trihalomethanes (TTHMs)However, Chloroform or Bromoform will always constitute the higher portion of the TTHMs.Bromoform is produced in coastal areas due to brackish intrusion and varies by well. Bromoform is formed by the reaction of Cl on Bromide.Chloroform is present in inland areas and varies by well.Trihalomethanes are a particular class of products that form by the reaction of chlorine with the organic constituents found in the natural waters.Although there are many trihalomethanes that form when organic material comes in contact with free chlorine, only four THM compounds are regulated. The four regulated trihalomethanes are chloroform, bromoform, Bromodichloromethane andDibromochloromethane. The sum of the concentrations of these compounds is known as TTHMs.
27 Where TTHMs are Formed High Water Age (MRT) Storage Tanks with poor water turnoverLow Demand AreasStagnant & Slow Moving Water AreasDead Ends Pipelines (MRT)Note: Unlined CI Pipe (systems in existence before 1949) require higher residual chlorine levelsUnlined CI Pipe Tuberculation with Bacterial Growth producing Organic Precursors
28 Production of Haloacetic Acids Like THMs, Haloacetic Acids are produced by the addition of free chlorine to waterscontaining natural organic materials.These 5 compounds are regulated as HAA5s.Monochloroacetic AcidMonobromoacetic Acid Dichloroacetic AcidDibromoacetic AcidTrichloroacetic AcidThese compounds will begin to degrade a few days after formation.They can not be removed by air stripping.Production of haloacetic acids are also formed in a similar fashion as trihalomethanes. When chlorine is added to water containing organic materials both Trihalomethanes and Haloacetic Acids will form. Although there are many haloacetic acids, EPA has chose to regulate the 5 compounds that are most commonly formed and pose the biggest health threat.Haloacetic acids develop more slowly under normal conditions of temperature and pH than Thrihalomethanes. Like THMs, Haloacetic acids will continue to form as long as free chlorine is present. Under high temperatures that occur in summer months and when free chlorine is not available, HAAs will biodegrade.
29 Where HAA5s are Found Low Demand Areas Toward Middle System Areas w/ high Chlorine concentration and low movementNear High Chlorine Dose and/or Residual LocationsHigh Bacterial Growth internal to systemHAA5 will degrade in systems with high water age, thus highest HAA5s are not found at MRT
30 Ratio of TTHM to HAA5Ratios of TTHM to HAA5 should remain relatively constantLarge variations indicate a change of system conditionsSince HAA5’s decay, an increase in HAA5 levels indicates that water age has declinedAn increase in both would mean that Cl residuals are too highTrending of changes can be very valuable for troubleshooting
31 Chlorine Dose and Its Effect on DBP Production This chart shows the increase in TTHMs and HAA5s associated with increasing the dose of free chlorine. A doubling of the chlorine dose causes a 60% rise in the production of HAA5s and a 23% rise in TTHMs in a short contact period.Typical Chlorine Doses may range between 2 mg/l to 4 mg/l with Chlorine Residual leaving the plant at an average near 1.5 mg/l.Often Chlorine Residual Concentration can be lowered proving significant reductions in DBP production.
32 DBP Formation Potential Indicates Significance of DBP Problem DBP Yield%Formation PotentialSimulatedDist. Sys. TestTOX*100%N/ATTHM23%7%HAA533%11%Other DBPs44%Tests have been performed on the potential for DBP formation based on 100% chlorine reaction with Organic Compounds. As can be seen from this chart a little over 50% of the DBP produced will be either THMs or specific Haloacetic acids that are regulated. The other 44%+ are unknown compounds.The other interesting feature of this chart is that organic compounds in source water contain both fulvic and humic compounds and thus under simulated conditions do not react with all the organic material present. The actual reactive constituents will fall somewhere between the ranges shown depending on the chlorine concentration, the contact time, pH and temperature. Long contact times in the presence of free chlorine can eventually approach the upper limits shown on the chart.Water Age* TOX = Total Organic HalidesAfter Watson and Montgomery AWWA Water Quality and Treatment, 1999
33 Formation of DBP in a Typical Water Treatment and Distribution System
34 Identifying the Point of DBP Production in a Water System DBPs are equally produced in the treatment plant and in the WD system.It is important to note where the DBPs are produced (extra sampling) to identify effective corrective actions.Typically DBP problems occur at MRT Locations.Proactive DBP Strategies should be targeted.
35 Effects of Moving the Point of Disinfection Moving the Point of Disinfection acts in three ways:Decreases significantly the time that the highest free chlorine concentration is in contact with organic material.Treatment, especially coagulation, sed. and filtration removes a portion of the TOC.In combining 1 & 2 above, the dose requirement for chlorine is lower and easier to predictMoving the point of disinfection is effective because TOC is being removed at each step in the treatment process. By moving the application point from a pre-chlorination point to a post sedimentation point in this example both THM and HAA5s have been reduced by over 50%!Surface Water Process Treatment provides significant TOC reduction. However, any treatment process used provides some level of TOC reduction.
36 Effective Chlorination System Modification Strategies DisinfectionLocationActionBenefitChlorine FeedReduce chlorine feed rates while maintaining proper chlorine residualsFewer DBPs formed in the water system. No / little cost for this option.Chlorine Injection PointChange point of chlorine injection to reduce the age of chlorinated waterFewer DBPs formed in the water system. Small cost for this option.Chlorine Injection BoostersAdd chlorine injection point(s) to boost Chlorine residuals in the distribution system instead of at the plantLower total chlorine added at the plant site. Fewer DBPs formed in the distribution system.Alternate Disinfection / ApplicationUse of chloramines in distribution systems with long detention times or selective use of preoxidation or oxidant such as NaMnO4Fewer DBPs formed in the water system. Costs for this option could be significant.Because in excess of 90% of the water treatment plants use chlorine as the primary disinfectant, adopting modifications to disinfection strategies can be very effective in reducing the production of DBP. These modifications are generally much more cost effective than changing treatment processes or using alternative disinfectants.
37 Water Age and DBP Production Other than Reducing Cl dose and residual levels, reducing water age is the most effective method available for reducing TTHM concentrations.There are two slopes present in TTHM development, The first is most significant and is related to Cl dose, the second is slower and related to Cl residualCL ResidualCL doseThis plot shows the relationship to TTHM formation and residence time. Note that the chloramine shows little change in TTHM formation until after a period of a couple of days. In this case the chloramine has been biodegraded to free chlorine and is now producing TTHMs at the same rate as the free chlorine.Franchi and Hill, 2002
38 Typical Distribution System Water Age (Days) PopulationMiles of WMMin RTMRT> 750,000> 1,0001 day~ 1 wk< 100,000<~ 2 wks< 25,000<~ 1 mo.Many water distribution systems have extremely high water ages. Water with high water age will frequently not have enough chlorine residual leading to growth of bacteria in dead end distribution lines and in storage tanks. The sediment that has been deposited in the dead end lines and in the water tanks will contain concentrations of compounds that will support biological growth.AWWA: Water Age for Ave and Dead End Conditions
39 Flushing Objectives Used in Water Distribution Systems Conventional Flushing< 2.5 fps velocity that reduces water age, raises disinfectant residual removes coloration&Unidirectional Flushing> 2.5 fps velocity that removes solid deposits and biofilm from pipelines
40 Removing Sediment and Biofilm from Water Mains by Unidirectional Flushing Sediment deposits and most biofilm can be removed if cleansing velocities can be achievedThe velocity that needs to be developed is 2.5 to 5 fps; these velocities will cause pressure drops and movement of sediment including rust to customer’s plumbingTo achieve these types of velocities without problems, a planned unidirectional approach must be used that valves off piping to force water to a certain location
41 Effects of pH on the Production of DBPs in Distribution System TTHM and HAA% Formation PotentialNote:HAA5pHThe graph on the left shows the effects of pH in the production of THMs over a 150 hour period. It can be seen that as the pH rises more TTHMS are produced.The plot on the right shows the same situation compared to HAA5 production. It can be observed that HAA5s are less susceptible to pH increases and actually have decreased. This is due to the biodegredation of the HAA5 over a long period of time.Franchi et al. 2002Amy et al. 1987
42 Problems with Water Turnover and Sediments in Tanks Increasing Bacterial Growth: 1. ) protection from UV, 2.) moderate high Temp., 3.) mildly alkaline pH (7.4 – 8.4) , 4.) O2 present and 5.) substrate for growthSediments contain significant concentrations of organic nutrients and exert a disinfectant demand leading to higher Cl dosesSediments provide protective layers for biofilms which allow pathogens to repairSediments encourage the growth of slow growing nitrifying bacteria that lower Cl residualBacteria contribute organics that lead to the formation of DBPsBacterial growth lead to turbidity, taste and odor problems that require higher Cl doseStorage Tank Water Movement: 1.) Daily goal of 50% storage volume removed, 2.) Minimum of 20% - 30% , and Target of every 3 daysSediments are the ideal place for development of biofilm since all conditions needed for bacterial growth are provided. Bacteria that are slow growing can colonize in these biofilms and produce compounds that exert high chlorine demands. Since the bacteria are protected from chlorine by the biofilm typical chlorination practices will not be effective.These biofilms can cause other problems too such as turbidity, taste and odor problems that may be pronounced in certain areas of the distribution system.Removal of the sediments that support these conditions is the most effective way of addressing the problem.
43 DEP Flushing Removal Requirements Flushing ProgramSuggestedActions/DEP RuleBenefits toTreatment SystemWritten Flushing ProceduresSubmit a Written Water Main Flushing Program.DEP RuleSampling is during normal operating conditions, and is not valid if you ONLY flush the day you are collecting samplesTreatment Components in Contact With WaterClean & remove biogrowths, calcium or iron / manganese deposits, & sludgeDEP Rule (2)Improves water quality, reduces chlorine demand & regrowth in the water system.Reservoirsand Storage TanksClean & remove biogrowths, Ca or Fe / Mn deposits, & sludge from storage tanks.DEP Rule (2) FACImproves water quality, reduces chlorine demand & biological regrowth in the water system.WaterDistribution MainsBegin systematic flushing of water system from treatment plant to system extremities.Dead-End Water MainsFlushing (every other day) or Automatic Flushing.Improves water quality,& reduces biological regrowth.Disinfection By-Product Management begins with an aggressive bio-film cleaning and flushing program for storage tanks, treatment units and the entire water system. As water ages more Disinfection By-Products are formed. Anything over two to three days old can be a problem. DEP has included requirements in FAC to ensure that DBP potentials are minimized. To ensure compliance and protection from potential DBP formation, FRWA recommends these proactive steps.
44 Use of Disinfectant Strategies Reduce Dosing Concentration of DisinfectantChange Points of ApplicationChange forms of DisinfectantUse of Multiple DisinfectantsChange DisinfectantUse of Orthophosphate in WD systems that use Unlined CI PipeExcess free chlorine in the presence of organic materials in the water will result in higher levels of DBP. For this reason use of chlorine prior to removal of TOC should be minimized. Fortunately chlorine is more effective in warmer weather and smaller doses may still be effective.Another method found to be successful is to change the points of application to minimize the contact with untreated surface water. DBP formation has found to be reduced as much as 50% when disinfection follows the coagulation process.Some water systems have elected to use chloramines instead of chlorine. Chloramines are significantly less reactive but still provide for the inactivation of pathogens. Chloramines are produced by the addition of ammonia.Some systems have elected to use multiple disinfectants. For example, free chlorine may be used as the primary disinfectant and chloramines are used to provide disinfectant residual. Injection of ammonia with chlorine forms chloramines and has a much lower potential of forming Disinfection By-Products, like Trihalomethanes.Because of the inability to control the production of DBP, alternatives disinfectants such as Ozone; Chlorine Dioxide; Potassium Permanganate; Ultraviolet Light; and Advanced Oxidation Processes.
45 Advantages in the Use of Chloramine Chloramines Not As Reactive With Organic Compounds so significantly less DBPs will formChloramine Residual are More Stable & Longer LastingChloramines Provides Better Protection Against Bacterial Regrowth in Systems with Large Storage Tanks & Dead End Water Mains when Residuals are MaintainedSince Chloramines Do Not React With Organic Compounds; Less Taste & Odor ComplaintsChloramines Are InexpensiveChloramines Easy to Make
46 Chloramine Disadvantages Not As Strong As Other Disinfectantseg. Chlorine, Ozone, & Chlorine DioxideCannot Oxidize Iron, Manganese, & Sulfides.Sometimes Necessary to Periodically Convert to Free Chlorine for Biofilm Control in the Water Distribution System (Burn lasting 2 to 3 weeks)Chloramine Less Effective at High pHForms of Chloramine such as Dichloramine cause Treatment & Operating ProblemsExcess Ammonia Leads to NitrificationProblems in Maintaining Residual in Dead Ends & Other Locations
47 Nitrification Concerns in Water Storage Tanks with the Use of Chloramine Nitrification is the conversion of ammonia to nitrite then to nitrateOccurs in dark areas, at pH > 7, with at warm temperatures and long detentionNitrification problems occur with systems that use chloramine which contains excess ammonia that when released can support the nitrification processNitrite (intermediate product) will consume free chlorine and chloramine disinfectantsMust ensure that disinfectant residual levels are adequate (> 1.5 ppm chloramine; with 2.0 to 2.5 recm.)Nitrification is a common problem faced by utilities using chloramines for distribution system residual maintenance. Nitrification involves the growth of ammonia-oxidizing bacteria and the resulting production of nitrite, which exerts a chloramine demand. This can lead to a loss of chloramine protection. Once the conditions that favor nitrification have been established it will be difficult to bring the situation under control. For this reason, if chloramines are being used, tank residuals should be measured frequently and a drop in residual is a signal to initiate corrective actions
48 Nitrification Monitoring Indicators Higher Water Temperatures andDepressed Disinfectant LevelsElevated DBPsElevated Bacterial Counts (HPC)*Elevated Nitrate/Nitrite Levels for Chloramination SystemsHigh Corrosion PotentialDirect Nitrification Monitoring ineffective* HPC use organic carbon as food, include total coliform; Not to exceed 500/ml in 95% of samples
49 So far we have used only qualitative approaches to control the development of DBP compounds. The qualitative approach consists of adhering to treatment techniques and operations that have been shown to be successful in reducing DBP concentrations. These consists of general rules for keeping free chlorine residuals in check, reducing precursors by sound treatment techniques and reducing contact time by state regulated flushing programs and sediment removal.In this section we will briefly discuss the use of Troubleshooting guides. These guides provide treatment plant operators with a systematic and quantitative approach (use of metrics and trending) for identifying the root causes of DPB formation and minimizing the conditions that lead to their development.Troubleshooting DBP Problems Quantitative Approach to DPB Reduction Interactive Portion of PresentationBob’s Handouts