Transcript Reducing Disinfection Byproducts (DBP)

Review of the Production and
Control of Disinfection ByProducts (DBP’s)
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Goals of DBP Review
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Review Disinfection By-Product MCL’s
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
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DEP MCL Requirements for DBP’s
TTHM, HAA5, Chlorite and Bromate
– TTHM
– HAA5
– Chlorite
– Bromate
.080 mg/l
.060 mg/l
1.0 mg/l*
0.010 mg/l **
* associated with the use of Chlorine Dioxide
** naturally occurring precursor in systems
near saltwater, associated with use of Ozone
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Disinfection Byproducts
Formation
NOM + Cl2
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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 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)
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Sources of Natural Organic Material
(NOM) in Surface Water
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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
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concentration.
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
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Raw Water Considerations
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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.
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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
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Typical Values of TOC for
Various Waters
Type of Water
Range in
mg C/l
Sea Water
0.5 – 5.0
WMD
NWFWMD
Most Ground
Water
0.1 – 5.0
Surface Water
1.0 – 20
Swamp Water
75 – 300
Effluents
Biotreatment
8.0 – 20
Wastewater
50 – 1000
InterFloridan
Mediate Median
Median mg C/l
6.1
<1.0
SRWMD
<1.0
2.0
SJRWMD
5.5
3.3
SWFWMD
9.8
16.8
SFWMD
6.3
1.9
STATE
4.8
2.2
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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 contamination
N
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Karst Features
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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
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Reducing the Production of
Disinfection By-Products
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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
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Coagulation to Remove TOC
TOC Removal using
Enhanced Coagulation for Surface Water Plants (TT)
TOC
Mg C/L
Alkalinity (CaCO3)
0-60
60-120
>120
Florida Source Waters
2.0 to 4.0
4.0 to 8.0
>8.0
35%
45%
50%
25%
35%
40%
15%
25%
30%
Typically Alum is used and requires sedimentation/filtration
Lime can also be used but has less ability due to high pH
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Other Means to Remove TOC
Permanganate
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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
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With 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
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Factors Affecting Disinfection
By-Product Production w/ Cl2
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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
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Oxidation/Reduction Only
DBP
Production
DBPs
Remain
Chloramines
Breakpoint Chlorination Curve
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Steps in the Formation of DBPs
with Free Chlorine
1.
2.
3.
4.
5.
6.
7.
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 Demand
Iron 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.
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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
2.53
* Note: Actual amount of oxidant must be about 15% – 20% higher
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DEP H2S Treatment
Requirements
Potential Impact
Water Quality Ranges
Water Treatment
Low
Total Sulfide < 0.3 mg/l
Direct
Chlorination
Moderate
pH < 7.2 Total Sulfide < 0.6 mg/l
pH > 7.2 Total Sulfide < 0.6 mg/l
Aeration
Aeration w/ pH
adjustment
Significant pH < 7.2 Total Sulfide < 0.6 mg/l
pH > 7.2 Total Sulfide < 0.6 mg/l
Forced Draft
Forced Draft w/
pH adjustment
Very Significant
Packed Tower w/
pH adjustment
Total Sulfide < 3.0 mg/l
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DEP Iron Treatment
Requirements
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State Secondary Standards require Iron to be
< 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 pH’s
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Treatment Issues with Sulfide
and Iron in Unlined CI Pipes
> 0.3 mg/l
Problematic
because of
colloidal solids
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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
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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
Chlorine Disinfecting Power and
pH Considerations in Water
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Chlorine reacts with water
Producing hypochlorous acid (HOCl) and the
hypochlorite ion (OCl-)
Chlorine is more reactive at lower pHs.
Low pH forms > HAA5s, High pH forms > TTHMs
Old Hypochlorite
contributes to
DBP formation
because doses
must be higher!
%
%
OCL-
HOCL
pH
6
7 8
9
Hypochlorite (pH
12.5) raises pH at
high dose levels!
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Sources of Chlorine and
Bromine in DBP Compounds
Chlorine
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Free Chlorine
Improper NH3
application
Poor Chemical
Mixing
Chloramine
Breakdown
Bromine
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Bromide from
Saltwater or
Brackish Water
Intrusion
Drought Conditions
Presence of Free
Chlorine
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Effect of the Addition of Free
CL at MCL+ Level with TOC
CL at 4.3 PPM
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%.
Florida Source Water often apporach 4 mg/l TOC
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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.
Flow
Paced
Control
In times when demand exceeds
average demand, a time-paced Cl feed
system overfeeds chlorine.
Production of Total Trihalomethanes
(TTHMs)
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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)
Bromodichloromethane
Bromoform (can be >70% coastal)
Dibromochloromethane
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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.
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Chloroform is present in inland areas and varies by well.
Where TTHMs are Formed
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High Water Age (MRT)
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Storage Tanks with poor water
turnover
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Low Demand Areas
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Stagnant & Slow Moving Water
Areas
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Dead Ends Pipelines (MRT)
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Note: Unlined CI Pipe (systems in
existence before 1949) require
higher residual chlorine levels
Unlined CI Pipe
Tuberculation with
Bacterial Growth
producing Organic
Precursors
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Production of Haloacetic Acids
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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.
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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
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Ratio of TTHM to HAA5
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Ratios of TTHM to HAA5 should remain
relatively constant
Large variations indicate a change of system
conditions
Since HAA5’s 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
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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.
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DBP Formation Potential Indicates
Significance of DBP Problem
DBP Yield
%
TOX*
TTHM
HAA5
Other DBPs
Formation
Simulated
Potential Dist. Sys. Test
100%
23%
33%
44%
N/A
7%
11%
N/A
Water Age
* TOX = Total Organic Halides
After Watson and Montgomery AWWA Water Quality and 32
Treatment, 1999
Formation of DBP in a Typical Water
Treatment and Distribution System
~ 50%
Treatment
~ 50%
Distribution
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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.
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Effects of Moving the Point of
Disinfection
Moving the Point of Disinfection
acts in three ways:
Surface Water Process Treatment
provides significant TOC reduction.
However, any treatment process used
provides some level of TOC reduction.
1.
Decreases significantly the time
that the highest free chlorine
concentration is in contact with
organic material.
2.
Treatment, especially
coagulation, sed. and filtration
removes a portion of the TOC.
3.
In combining 1 & 2 above, the
dose requirement for chlorine
is lower and easier to predict
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Effective Chlorination
System Modification Strategies
Disinfection
Location
Chlorine Feed
Chlorine
Injection Point
Chlorine
Injection
Boosters
Alternate
Disinfection /
Application
Action
Benefit
Reduce chlorine feed
rates while maintaining
proper chlorine residuals
Fewer DBPs formed in the water
system. No / little cost for this
option.
Change point of chlorine
injection to reduce the
age of chlorinated water
Fewer DBPs formed in the water
system. Small cost for this
option.
Add chlorine injection
point(s) to boost Chlorine
residuals in the
distribution system
instead of at the plant
Use of chloramines in
distribution systems with
long detention times or
selective use of
preoxidation or oxidant
such as NaMnO4
Lower total chlorine added at the
plant site. Fewer DBPs formed in
the distribution system.
Fewer DBPs formed in the water
system. Costs for this option
could be significant.
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Water Age and DBP
Production
CL
dose
CL Residual
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
Franchi and Hill, 2002
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Typical Distribution System
Water Age (Days)
Population Miles of WM
Min RT
MRT
> 750,000 > 1,000
1 day
~ 1 wk
< 100,000 <
400
1 day
~ 2 wks
< 25,000 <
100
1 day
~ 1 mo.
AWWA: Water Age for Ave and Dead End Conditions
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Flushing Objectives Used in Water
Distribution Systems
Conventional Flushing
& Unidirectional Flushing
< 2.5 fps velocity that reduces
water age, raises disinfectant
residual removes coloration
> 2.5 fps velocity that removes
solid deposits and biofilm from
pipelines
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Removing Sediment and Biofilm from
Water Mains by Unidirectional Flushing
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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
customer’s 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
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Effects of pH on the Production of
DBPs in Distribution System
TTHM and HAA% Formation Potential
pH
Note:
HAA5
Amy et al. 1987
Franchi et al. 2002
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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
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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
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removed, 2.) Minimum of 20% - 30% , and Target of every 3 days
DEP Flushing Removal
Requirements
Flushing
Program
Suggested
Actions/DEP Rule
Benefits to
Treatment System
Written
Flushing
Procedures
Treatment
Components
in Contact
With Water
Submit a Written Water Main
Flushing Program.
DEP Rule 62-555.350
Sampling is during normal operating
conditions, and is not valid if you
ONLY flush the day you are
collecting samples
Clean & remove biogrowths,
calcium or iron / manganese
deposits, & sludge
DEP Rule 62-555.350(2)
Improves water quality, reduces
chlorine demand & regrowth in the
water system.
Reservoirs
and Storage
Tanks
Clean & remove biogrowths,
Ca or Fe / Mn deposits, &
sludge from storage tanks.
DEP Rule 62-555.350(2) FAC
Improves water quality, reduces
chlorine demand & biological
regrowth in the water system.
Water
Distribution
Mains
Begin systematic flushing of
water system from treatment
plant to system extremities.
Dead-End
Water Mains
Flushing (every other day)
or Automatic Flushing.
DEP Rule 62-555.350(2)
Improves water quality, reduces
chlorine demand & biological
regrowth in the water system.
Improves water quality,& reduces
biological regrowth.
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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
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Advantages in the Use of
Chloramine
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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
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Chloramines Easy to Make
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
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Nitrification Concerns in Water Storage
Tanks with the Use of Chloramine
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Nitrification is the conversion of ammonia to nitrite
then to nitrate
Occurs in dark areas, at pH > 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
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adequate (> 1.5 ppm chloramine; with 2.0 to 2.5 recm.)
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
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* HPC use organic carbon as food, include total coliform; Not to exceed
500/ml in 95% of samples
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Troubleshooting DBP
Problems
Quantitative Approach to DPB
Reduction
Interactive Portion of
Presentation
Bob’s Handouts
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