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Title: Review of the Production and Control of Disinfection By-Products (DBP


1
Review of the Production and Control of
Disinfection By-Products (DBPs)
2
Goals of DBP Review
  • Review Disinfection By-Product MCLs
  • Review How DBPs are Formed
  • Review Water Sources and ID Conditions that
    Contribute to a DBP Problem
  • Identify Measuring Parameters Associated with NOM
    and TOC
  • Identify DBP Best Management Practices
  • Review DBP Troubleshooting Guide
  • Conduct Interactive Role Playing Exercise

3
DEP MCL Requirements for DBPs TTHM, HAA5,
Chlorite and Bromate
  • TTHM .080 mg/l
  • HAA5 .060 mg/l
  • Chlorite 1.0 mg/l
  • Bromate 0.010 mg/l
  • associated with the use of Chlorine Dioxide
  • naturally occurring precursor in systems
    near saltwater, associated with use of Ozone

4
Disinfection Byproducts Formation
NOM Cl2 THMs HAAs Other DBP
Compounds
  • Disinfection 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 DBPs 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)

5
Sources of Natural Organic Material (NOM) in
Surface Water
  • Rain Events wash organic matter into receiving
    body.
  • Flooding reverses flow gradients in upper
    aquifers
  • Cavities and Fissures in Karst Conditions allow
    surface intrusion
  • Poor Sanitary Conditions, i.e., broken seals,
    abandoned wells, poor locations, result in
    intrusion
  • Ground Water that has high NOM content is
    indicative of the intrusion from Surface Water
  • Sedimentation, biogrowth or poor flushing
    practices in distribution systems increase
    organics concentration.

6
Use of Different Carbon Surrogates
  NOM Species   Description   Significance
TOC Total amount of all forms of Organic Carbon Present Good overall indicator of potential DBP problems
DOC The TOC passing through a 0.45 micron filter is dissolved Better indicator of the reactive portion of the TOC
UV254 Used to identify light absorption of reactive humic components Identifies the reactive potion of the DOC
SUVA Ratio of UV254 to DOC Best 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 GW
  • If Surface water mixes with ground water, each
    well may experience different levels of TOCs.
  • The humic content can be approximated by using
    SUVA.

8
Organic Carbon (TOC) or Precursors in Natural
Waters mg/l
Mean Surface Water 3.5
Sea Water
Ground Water
Surface Water
Swamp
Wastewater
Wastewater Effluent
.1 .2 .5 1.0 2 5 10 20 50 100
200 500 1000
9
Typical Values of TOC for Various Waters
Type of Water Range in mg C/l
Sea Water 0.5 5.0
Most Ground Water 0.1 5.0
Surface Water 1.0 20
Swamp Water 75 300
Effluents Biotreatment 8.0 20
Wastewater 50 1000
WMD Inter-Mediate Median Floridan Medianmg C/l
NWFWMD 6.1 lt1.0
SRWMD lt1.0 2.0
SJRWMD 5.5 3.3
SWFWMD 9.8 16.8
SFWMD 6.3 1.9
STATE 4.8 2.2
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, Floridas
    primary source of drinking water, from potential
    contamination

N
11
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.

Light areas indicate Karst features
12
Reducing the Production of Disinfection
By-Products
  • Eliminating Sources of Surface Water into
    Production Wells
  • Selecting Well Blends with Lower DBPs
  • Removing Precursor Material within treatment
    process
  • Changing the Point(s) of Chlorine Application
  • Lowering the Chlorine Dose and/or Residual
  • Using Alternate Disinfection Strategies
  • Ensuring the WTP processes are absent of organic
    growth (ie. Ion Exchange and Activated Carbon
    Systems)
  • Ensuring Water Tank Turnover
  • Reducing Distribution System Water Age
  • Flushing water in slow moving areas and at
    dead-ends
  • Removing sediment that creates chlorine demand
  • Removing biofilm that converts inorganic to
    organic materials

13
Coagulation to Remove TOC
TOC Removal using Enhanced Coagulation for
Surface Water Plants (TT)
  • TOC Alkalinity (CaCO3)
  • Mg C/L 0-60 60-120 gt120
  • 2.0 to 4.0 35 25 15
  • 4.0 to 8.0 45 35 25
  • gt8.0 50 40 30

Florida Source Waters
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
  • Permanganate
  • Long Used for Taste and Odor
  • Removes color forming substances which are the
    same constituents that cause DBP formation
  • Range 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 reported
  • Limitation is that can not be used in systems
    with High Sulfide Levels or with changing
    conditions
  • Activated Carbon Filter
  • With Source Water TOC from 2 to 4 mg C/L
    Activated Carbon Systems typically remove gt50
  • 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 present
  • Concentration of Chlorine added and how well it
    is mixed
  • Bromide Ion Concentration
  • Presence of H2S, Iron and NH3
  • Age of Water System (amt of CI pipeline)
  • Warmer Temperatures
  • Longer Contact Times (MRT)
  • Presence of Sediment in Tanks

16
Oxidation/Reduction Only
DBPs Remain
DBP Production
Chloramines
Breakpoint Chlorination Curve
17
Steps in the Formation of DBPs with Free
Chlorine
  1. Inorganic reducing constituents such as H2S, Fe
    Mn and NH3 compounds react first (oxidation
    reduction reaction).
  2. When Iron, Sulfide or NH3 are present, they exert
    the major Chlorine Demand
  3. Iron concentrations are required in the Secondary
    Standard submittal but Sulfide or NH3 are not.
  4. If there are products of Biological Metabolism
    such as Nitrite this will also react. (Important
    in Nitrification)
  5. Any readily soluble Organic Materials in the
    water (TOC) will then react forming DBPs.
  6. Further Free Chlorine addition will not destroy
    DBPs.
  7. Disinfection jar test can be used to identify
    reducing constituents but will not identify by
    specific constituent.

18
Example of Calculating CL2 Demand
Water Quality actual mg/l CL2 Multiplier Total CL2 Demand
Fe 0.3 0.64 0.19
Mn 0.06 1.3 0.07
H2S 0.2 2.1 0.42
NO2 0.1 5 0.50
NH3 0.1 10 to 12 1.20
Org-N 0.05 1 0.05
TOC 1.0 0.1 0.10
Chlorine Demand Chlorine Demand 2.53
Note Actual amount of oxidant must be about
15 20 higher
19
DEP H2S Treatment Requirements
Potential Impact Water Quality Ranges Water Treatment
Low Total Sulfide lt 0.3 mg/l Direct Chlorination
Moderate pH lt 7.2 pH gt 7.2 Total Sulfide lt 0.6 mg/l Total Sulfide lt 0.6 mg/l Aeration Aeration w/ pH adjustment
Significant pH lt 7.2 pH gt 7.2 Total Sulfide lt 0.6 mg/l Total Sulfide lt 0.6 mg/l Forced Draft Forced Draft w/ pH adjustment
Very Significant Total Sulfide lt 3.0 mg/l Packed Tower w/ pH adjustment
20
DEP Iron Treatment Requirements
  • State Secondary Standards require Iron to be lt
    0.30 mg/l in the finished water
  • Thus water systems with iron concentration
    greater than 0.3 mg/l would need to install
    filters
  • Iron may be sequestered up to a concentration of
    1.0 mg/l
  • In an aeration system Iron is removed by raising
    the pH while H2S is removed better at lower pHs

21
Treatment Issues with Sulfide and Iron in Unlined
CI Pipes
gt 0.3 mg/l Problematic because of colloidal solids
  • Sulfide is remove by lowering pH and filtering
  • Unreacted Sulfide will form blackwater with
    unlined CI pipes
  • Sulfate and Colloidal Sulfur can be reconverted
    to sulfide by bacteria in water tanks causing
    odor
  • Iron is removed by raising pH and filtering
    source water
  • Unfiltered Iron will result in red water
    complaints
  • Iron can also be a corrosion product from unlined
    CI pipes
  • Iron will result in staining

22
Chlorine Disinfecting Power and pH
Considerations in Water
  • Chlorine reacts with water
  • Producing hypochlorous acid (HOCl) and the
    hypochlorite ion (OCl-)
  • Chlorine is more reactive at lower pHs.
  • Low pH forms gt HAA5s, High pH forms gt TTHMs

Old Hypochlorite contributes to DBP formation
because doses must be higher!
Hypochlorite (pH 12.5) raises pH at high dose
levels!
HOCL
OCL-
6 7 8 9
pH
23
Sources of Chlorine and Bromine in DBP Compounds
  • Chlorine
  • Free Chlorine
  • Improper NH3 application
  • Poor Chemical Mixing
  • Chloramine Breakdown
  • Bromine
  • Bromide from Saltwater or Brackish Water
    Intrusion
  • Drought Conditions
  • Presence of Free Chlorine

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 PPM
Florida Source Water often apporach 4 mg/l TOC
25
Chlorine Detention Time Small System
Ave Demand
Time Paced Control
Water 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 gt70 inland)
    Bromodichloromethane
  • Bromoform (can be gt70 coastal)
    Dibromochloromethane
  • The 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.

27
Where TTHMs are Formed
  • High Water Age (MRT)
  • Storage Tanks with poor water turnover
  • Low Demand Areas
  • Stagnant Slow Moving Water Areas
  • Dead Ends Pipelines (MRT)
  • Note Unlined CI Pipe (systems in existence
    before 1949) require higher residual chlorine
    levels

Unlined 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 waters
  • containing natural organic materials.
  • These 5 compounds are regulated as HAA5s.
  • Monochloroacetic Acid
  • Monobromoacetic Acid
    Dichloroacetic Acid
  • Dibromoacetic Acid
  • Trichloroacetic Acid
  • These compounds will begin to degrade a few days
    after formation.
  • They can not be removed by air stripping.

29
Where HAA5s are Found
  • Low Demand Areas
  • Toward Middle System Areas w/ high Chlorine
    concentration and low movement
  • Near High Chlorine Dose and/or Residual Locations
  • High Bacterial Growth internal to system
  • HAA5 will degrade in systems with high water age,
    thus highest HAA5s are not found at MRT

30
Ratio of TTHM to HAA5
  • Ratios of TTHM to HAA5 should remain relatively
    constant
  • Large variations indicate a change of system
    conditions
  • Since HAA5s decay, an increase in HAA5 levels
    indicates that water age has declined
  • An increase in both would mean that Cl residuals
    are too high
  • Trending of changes can be very valuable for
    troubleshooting

31
Chlorine Dose and Its Effect on DBP Production
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 Potential Simulated Dist. Sys. Test

TOX 100 N/A
TTHM 23 7
HAA5 33 11
Other DBPs 44 N/A
Water Age
After Watson and Montgomery AWWA Water Quality
and Treatment, 1999
TOX Total Organic Halides
33
Formation of DBP in a Typical Water Treatment and
Distribution System
50 Treatment
50 Distribution
34
Identifying the Point of DBP Production in a
Water System
  1. DBPs are equally produced in the treatment plant
    and in the WD system.
  2. It is important to note where the DBPs are
    produced (extra sampling) to identify effective
    corrective actions.
  3. Typically DBP problems occur at MRT Locations.
  4. 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 predict

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
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
residual
CL Residual
CL dose
Franchi and Hill, 2002
38
Typical Distribution System Water Age (Days)
Population Miles of WM Min RT MRT
gt 750,000 gt 1,000 1 day 1 wk
lt 100,000 lt 400 1 day 2 wks
lt 25,000 lt 100 1 day 1 mo.
AWWA Water Age for Ave and Dead End Conditions
39
Flushing Objectives Used in Water Distribution
Systems
Unidirectional Flushing gt 2.5 fps velocity that
removes solid deposits and biofilm from pipelines
Conventional Flushing lt 2.5 fps velocity that
reduces water age, raises disinfectant residual
removes coloration

40
Removing Sediment and Biofilm from Water Mains by
Unidirectional Flushing
  • Sediment deposits and most biofilm can be removed
    if cleansing velocities can be achieved
  • The 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
    customers plumbing
  • To 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 Potential
Note HAA5
pH
Franchi et al. 2002
Amy 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 growth
  • Sediments contain significant concentrations of
    organic nutrients and exert a disinfectant demand
    leading to higher Cl doses
  • Sediments provide protective layers for biofilms
    which allow pathogens to repair
  • Sediments encourage the growth of slow growing
    nitrifying bacteria that lower Cl residual
  • Bacteria contribute organics that lead to the
    formation of DBPs
  • Bacterial growth lead to turbidity, taste and
    odor problems that require higher Cl dose
  • Storage Tank Water Movement 1.) Daily goal
    of 50 storage volume removed, 2.) Minimum of 20
    - 30 , and Target of every 3 days

43
DEP Flushing Removal Requirements
44
Use of Disinfectant Strategies
  • Reduce Dosing Concentration of Disinfectant
  • Change Points of Application
  • Change forms of Disinfectant
  • Use of Multiple Disinfectants
  • Change Disinfectant
  • Use of Orthophosphate in WD systems that use
    Unlined CI Pipe

45
Advantages in the Use of Chloramine
  • Chloramines Not As Reactive With Organic
    Compounds so significantly less DBPs will form
  • Chloramine Residual are More Stable Longer
    Lasting
  • Chloramines Provides Better Protection Against
    Bacterial Regrowth in Systems with Large Storage
    Tanks Dead End Water Mains when Residuals are
    Maintained
  • Since Chloramines Do Not React With Organic
    Compounds Less Taste Odor Complaints
  • Chloramines Are Inexpensive
  • Chloramines Easy to Make

46
Chloramine Disadvantages
  • Not As Strong As Other Disinfectants
  • eg. Chlorine, Ozone, Chlorine Dioxide
  • Cannot 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 pH
  • Forms of Chloramine such as Dichloramine cause
    Treatment Operating Problems
  • Excess Ammonia Leads to Nitrification
  • Problems 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 nitrate
  • Occurs in dark areas, at pH gt 7, with at warm
    temperatures and long detention
  • Nitrification problems occur with systems that
    use chloramine which contains excess ammonia that
    when released can support the nitrification
    process
  • Nitrite (intermediate product) will consume free
    chlorine and chloramine disinfectants
  • Must ensure that disinfectant residual levels are
    adequate (gt 1.5 ppm chloramine with 2.0 to 2.5
    recm.)

48
Nitrification Monitoring Indicators
  • Higher Water Temperatures and
  • Depressed Disinfectant Levels
  • Elevated DBPs
  • Elevated Bacterial Counts (HPC)
  • Elevated Nitrate/Nitrite Levels for
    Chloramination Systems
  • High Corrosion Potential
  • Direct Nitrification Monitoring ineffective

HPC use organic carbon as food, include total
coliform Not to exceed 500/ml in 95 of samples
49
Troubleshooting DBP Problems Quantitative
Approach to DPB Reduction Interactive Portion of
Presentation
Bobs Handouts
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