Chloramines: How to Dose, What to Worry About

Chloramines: How to Dose,
What to Worry About
Presented by:
Debra Cerda
Drinking Water Quality Team
Public Drinking Water Section
TCEQ Public Drinking Water Conference
August 9-10, 2005
Topics
! What are Chloramines?
! Why Change to Chloramines?
! Chemistry in Water
< Of Chlorine
< Of Chloramines
! Ratios & Dosing
< Chlorine to Ammonia
< Dosing for Different Types of Ammonia
Topics (continued)
!
!
!
!
The Balance & What’s at the Extremes?
Health Effects
One Extreme: Disinfection Byproducts
Other Extreme: Nitrification
< Why be concerned?
< What is it?
< How to prevent?
Bonus Topics
!
!
!
!
What to Look for & Where to Measure
What to Do “When Ratios Go Wrong”
Sources of NH3
Sequence of Injection
What Are Chloramines?
! Chloramines -family of compounds
used for disinfection.
< Monochloramine -NH2Cl
< Dichloramine - NHCl2
< Nitrogen trichloride - NCl3
! Chlorine + Ammonia = Chloramines
What Are Chloramines?
! Used in water treatment plants since 1930's
! Less effective than most other disinfectants
and a weaker oxidant
! Use of chloramines results in decreased
formation of many disinfection byproducts
(DBPs)
Why Change to Chloramination?
Disinfection Byproducts of Chlorine
! TTHM = Total Trihalomethanes
– Methane with three “halogens” on it
– Halogen - Chlorine or Bromine molecule
! HAA5 = Haloacetic acids (group of 5)
– Acetic acid with 1, 2, or 3 halogen
molecules
– Five are regulated
! Others not discussed today: HKs, HANs, CH
How do they form?
Every silver lining has a cloud
! Cl2 + Precursor = DBP
< Chlorine reacts with carbon to form DBPs
– Total Organic Carbon (TOC) is a surrogate
for disinfection by-product precursors
< More contact TIME leads to more DBPs
< Higher TEMPERATURE makes more
DBPs
! NOTE: You may not have to switch from
chlorine if you optimize process control!!
Special note for Texas:
We have naturally occuring BROMIDE here
! Bromide Ion [Br-]
– LOTS in E. Texas and
Gulf (0.2 to 1.2 mg/L)
Bromide
Bromide
! Cl2 + Precursor (+Br-) = DBP
< If you have more Br- . . . more DBPs
Bromine’s Contribution to DBPs
! The Br! concentration in the source water is
important, but is rarely measured. A few
generalizations are helpful in assessing the likely
relative concentration of bromide:
Why Change to Chloramination?
Other Disinfectants have Byproducts
! Chlorine Dioxide
< Chlorite (ClO2) - Acute respiratory
! Ozone
< Bromate (BrO3) - Strongly carcinogenic
Starting With the Basics:
Chlorination and Chloramination in
Water
Chemistry in Water: Chlorine
! Dissolution, Hydrolysis, and Dissociation
Cl2 + H2O º HOCl + Cl- + H+
H+
Cl -
(-)
H
O
Cl
O
Cl
Breakpoint Chlorination
! Addition of chlorine in quantities sufficient to
first satisfy the chlorine demand (including the
demand from nitrogen compounds originally in
water), and then produce a free chlorine residual
! Results in free chlorine residual
< Allows disinfectant properties of free
chlorine to be fully utilized
< Chloramination in drinking water treatment
occurs following breakpoint chlorination
1. Readily oxidizable, simple
components of source water
consume chlorine
2. Chlorine reacts with organic and
inorganic nitrogen in source water;
monochloramine is formed
2
1
Combined Chlorine Residual
3. Transition zone - free chlorine
residual created and destroyed at
same rate; monochloramine formed
4. Residual is destroyed; di- and trichloramine formed and destroyed.
4
2
3
1
Combined Chlorine Residual
5. Breakpoint - all available
nitrogen has been oxidized; free
chlorine begins to persist
6. Free chlorine residual
increases
6
4
2
3
Breakpoint!
5
Free Chlorine Residual
(HOCl and OCl -)
1
Combined Chlorine Residual
Breakpoint Chlorination & TCEQ
! Breakpoint chlorination (of raw water
constituents) when chloramines are used as
primary disinfectant
< NH3 is added after this (raw water) breakpoint
< Combines with free chlorine residual to form
NH2Cl.
< Ammonia (NH3) dose depends on free
chlorine residual, NOT chlorine dose
Applying the Concepts: Ratios
! If Cl2 goes in upstream (and it should for SW)
< Chlorine residual (not dose) measured
< Ammonia dose determined
! Why don’t we use chlorine dose?
< Free chlorine reacts with chemicals other than NH 3 in
source water
< Iron, manganese, hydrogen sulfide, organic matter
< Reactions result in:
– A reduction in color, taste, and odor
– Decreased amount of chlorine (HOCl) available to
form chloramines
Applying the Concepts: Ratios
! Other factors
< How much excess Cl2 was present
< pH - Effectiveness of chloramine
disinfection fairly consistent for pH 7 -9
Applying the Concepts: Ratios
! Goal is to get a good Cl2:NH3 ratio
< One mole of chlorine matched with one
mole of ammonia to form
monochloramine, NH2Cl
Chloramination Chemistry
H
Cl
N
H
H
H
N
H
H
H
O
Cl
H
Cl
Cl
H
N
H
Cl
Cl
Cl
N
N
H
Cl
O
Applying the Concepts: Ratios
! The key is the chlorine to ammonia ratio
! Forms of Chlorine:
< Sodium Hypochlorite
< Gaseous Chlorine
! Forms of Ammonia (NH3):
< Anhydrous Ammonia (gas)
< Ammonium Hydroxide
< Ammonium Sulfate (solid)
< Ammonium Sulfate (liquid)
Chlorine: Ammonia
(Cl2:NH3) Ratio
! Molecular weight
< Cl2 has a molecular weight of 71
< NH3 has a molecular weight of 17
418
. lbsCl2
1 mol Cl 2
71 lbs Cl 2
=
=
1 lb NH3
1 mol NH 3
17 lbs NH 3
(for anhydrous ammonia gas)
Cl2:NH3 . 4:1 (by weight) to form NH 2Cl
NH3 dose = ¼ of the Cl2 residual
Chlorine: Ammonia
(Cl2:NH3) Ratio
!
Cl2:NH3 = 4:1 most commonly used for water treatment
< At higher ratios:
– NHCl2 and NCl3 concentrations increase
– Higher production of DBPs
< At lower ratios (less chlorine):
– Chloramine is present as NH2Cl
– Lower production of DBPs
– Increased corrosion of copper and brass
– Excess NH3 can lead to nitrification in
distribution system
Other Ammonia Sources
! Ammonium hydroxide
< Solid
! NH4OH
O
H
H
H
N
H
H
H
H
N
H
H
O
O
S
O
O
H
H
! Ammonium sulfate
< Liquid or Solid
H
N
H
Chlorine: Ammonium Hydroxide
Cl2:NH4OH Ratio
! Ammonium hydroxide
< Cl2 has a molecular weight of 71
< NH4OH has a molecular weight of 35
1 mol Cl 2
71 lbs Cl 2
2.02 lbs Cl 2
=
=
1 mol NH 4 OH
35 lbs NH 4 OH
1 lb NH 4 OH
(for pure solid ammonium hydroxide)
Cl2:NH4OH . 2:1 (by weight) to form NH 2Cl
NH4OH dose = ½ of the Cl2 residual
Chlorine: Solid Ammonium Sulfate
Cl2:(NH4)2SO4 Ratio
! Ammonium sulfate
< (NH4)2SO4 has a molecular weight of 132
< Ammonium sulfate ((NH 4)2SO4) has more
“ammonia” (NH 3) than ammonium hydroxide
(NH4OH)
< Two molecules of Cl2 are needed
2 molCl2
1 mol(NH4 )2 SO4
142 lbsCl2
=
132 lbs(NH4 )2 SO4
108
. lbsCl2
=
1 lb(NH4 )2 SO4
(for pure solid ammonium sulfate)
Cl2 :(NH4)2SO4 . 1:1 (by weight) to form NH 2Cl
(NH4)2SO4 dose = the free Cl2 residual
Liquid Chemicals (like LAS)
! Concentration is usually reported on a weight to weight
(w/w) basis
< 38% (w/w) ammonium sulfate means that 1 lb of the
solution contains 0.38 lb of pure ammonium sulfate
((NH4)2SO4)
< In other words, it is diluted, so we need to account for
that in ratio
! Adjust the dose for feedstock concentration
108
. lbsCl2
1 lb ( NH4 )2 SO4
038
. lb ( NH4 ) 2 SO4
041
. lbs Cl 2
X
=
1 lb LAS
1 lb LAS
38% LAS dose = 2.5 X the free Cl2 residual
The Balance
& What’s at the Extremes?
! If ratio has excess chlorine , higher disinfection
byproducts (DBPs like TTHMs, HAA5s)
! If ratio has excess ammonia, nitrification
! Balance it out (work with the ratios)
Balancing Risk
Risk of
waterborne
disease
Risk of
cancer
RISK
DISINFECTION
Health Effects
Chloramines
! The ingestion of chloramines in drinking
water poses little health risk to healthy
people.
! Sensitive populations:
< Dialysis patients
< Aquatic organisms
Health Effects
Chloramines
! Dialysis
< Method of cleaning the blood of people with
kidney problems
< Membrane system with blood on one side,
tap water on the other; contaminants in blood
transferred to water
< Similarly, compounds (i.e., chloramine) are
transferred from the water to the blood
Health Effects
Chloramines
! Chloramines in the blood cause damage to red
blood cells, which can lead to hemolytic anemia
< Dialysis patients are exposed to large
amounts of water (70 - 80 times the
amount normally ingested)
< Therefore, dialysis patients could have
high exposure to chloramines if water
not filtered
Health Effects
Chloramines
! Aquatic organisms
< Both chloramines and NH3 are toxic and
can be fatal to fish
< Chloramines bind to iron in blood cells
and inhibit oxygen-carrying capacity
Health Effects
Chloramines
! Reducing the risk to sensitive populations
< Chloramines can be removed from water by:
– Granular activated carbon (GAC)
– Green sand zeolite
– Ascorbic acid (Vitamin C)
< Notifying dialysis facilities and fish hobbyists
and stores of changes to water due to
chloramination can reduce risks
– Allows implementation of treatment devices
Health Effects
Chloramines
! TCEQ approves use of chloramines on
case-by-case basis
– To receive approval, water utility must issue
public notice to customers and notify hospitals
and dialysis centers 14 days before converting to
chloramines (a greater warning period is
probably in best public/utility interest).
Health Effects
DBPs of Chloramines
! Chloramination creates fewer DBPs than free
chlorine
! Some DBPs are formed in higher amounts with
chloramines:
< Cyanogen chloride
– Irritation of eyes, skin, and respiratory tract
< N-nitrosodimethylamine (NDMA)
– Mutagenic, probable human carcinogen
– Greater health concern than THMs
– Present in higher concentrations in chloraminated
water than in chlorinated water
Health Effects
DBPs
! NDMA not currently regulated, but due to
potential health effects, some work is currently
in progress to identify ways to remove NDMA
from water
<
Air stripping, reverse osmosis, adsorption are NOT
effective means for removal
! UV appears to be effective
< Required dosage is higher than needed for viral
<
inactivation
Modifications to UV systems / operation could be
needed
One Extreme:
Disinfection Byproducts (DBPs)
! TTHM = Total Trihalomethanes
< 0.080 mg/L MCL based on RAA
< Carcinogenic, miscarriage (?)
! HAA5 = Haloacetic acids
< 0.060 mg/L MCL based on RAA
< Carcinogenic
! Stage 2 Disinfection Byproduct Rule-Locational
Running Annual Average (RAA)
Other Extreme:
Nitrification
! Chemical Issues
Biological Issues
Disinfection Depletion
Nitrite/Nitrate Formation
Dissolved Oxygen Depletion
Reduction in pH and
Alkalinity
DBP Formation due to
Mitigation Techniques
HPC Increase
AOB Increase
NOB Increase
Other Extreme:
Nitrification
Chemical Issues
Disinfection Depletion
Nitrite/Nitrate Formation
Dissolved Oxygen Depletion
Reduction in pH and
Alkalinity
DBP Formation due to
Mitigation Techniques
Biological Issues
HPC Increase
AOB Increase
NOB Increase
Other Extreme:
Nitrification
! Nitrite/Nitrate are acute health risks to infants up
to six months of age
< Methemoglobinemia (blue baby syndrome)
! Nitrite and bacterial growth consume
disinfectant
< Potential for violating Total Coliform Rule
! 1996 report estimated 63% of chloraminating
utilities showed signs of nitrification in
distribution system
Nitrification
! Microbial process by which reduced
nitrogen compounds (primarily ammonia)
are sequentially oxidized to nitrite (NO2-)
and nitrate (NO3)
Nitrification
! Ammonia converted to nitrite by ammoniaoxidizing bacteria (AOBs)
AOB
NO2-
NH3
! Can then be converted to nitrate by nitrite oxidizing bacteria (NOBs)
NOB
NO2-
NO3
Nitrifying Bacteria
! Ammonia-oxidizing Bacteria
< Nitrosomonas most frequently identified
< Nitrosococcus and Nitrosospira
! Nitrite-oxidizing Bacteria
< Nitrobacter
– Slow grower = process usually incomplete
Sources of Free Ammonia
! Naturally occurring
! Ammonia addition for chloramination
< Chloramine usage increase to reduce
trihalomethanes and haloacetic acid
formation
! Chloramine decay (Autodecomposition)
< Monochloramine optimal
Breakpoint Curve
Monochloramine
5:1
3:1
4:1
>8:1
7:1
Added chlorine (fixed N)
Increased Risk of Nitrification
! With temperature
! With increasing distance into distribution
system
! Older pipes (tuberculation)
! Absence of sunlight
! As disinfectant demand increases
! Note: Nitrifying bacteria observed growing
with chloramine residual as high as 1.5
mg/L
Growth Conditions for Nitrifying
Bacteria
! Temperature
B
B
< Optimal 25 -30 C; Range of
nitrification 8B -26B C
! pH
< Optimal 7.0-8.0; Range 6.6-9.7
! Chlorine to ammonia-nitrogen ratio of 3:1
! Inadequate disinfectant residuals
How to Minimize Nitrification
! Be PRO-active, not RE-active!
! Nitrification Monitoring Strategy
! Develop optimal preventative maintenance
program
! Optimize process control (Bonus slides)
Nitrification
- Monitoring Strategy ! Parameters
< Heterotrophic Plate Counts (HPCs)
< Free and total ammonia
< Nitrite and nitrate
< Disinfectant dose and residual
< Temperature
< pH
< DO, alkalinity, TOC, DOC
< Fish
Nitrification Monitoring Strategy
! Sampling locations:
< Raw water
< Finished water
< Reservoirs
< Dead-end mains
< Routine coliform monitoring stations
Nitrification Monitoring Strategy
! Use this data to establish baseline
! Watch for trends, for example:
< PH decreasing
< HPC increasing
< Free ammonia decrease
< Disinfectant demand increasing and
residual decreasing
< Nitrite increase
Preventative Measures
! Short term
< Periodic changes to free chlorine
< Flushing programs
! Moderate
< Reservoirs- Drain, clean, and inspect
< “Pigging”- mechanically clean D.S.
! Long term
< Booster stations to increase chloramine
residual
< Reservoir design and retrofitting
Flushing Program
“Shock” the System
! A reversion back to free chlorine may be needed
each year for at least two weeks
! Notify before and after the flush
< TCEQ so DBP samples delayed until the
NH2Cl levels are reestablished.
< The public to inform them of potential
changes in the water quality and how it
benefits them
Flushing Program
Unidirectional Flushing
! Proactively cleans the distribution system
by displacing poor quality with high
quality water while removing sediments
and biofilms within system through
scouring action
Uni-directional Flushing
! Before starting:
< Distribution Modeling- models the
hydraulic and water quality behavior of
water distribution piping systems.
< EPA NET 2.0- FREE public domain
software
Benefits of Controlling Nitrification
! Disinfectant residual persists throughout
the system
! Better protection against bacterial
regrowth
! Lower chlorine and ammonia doses
! Lower maintenance and monitoring costs
! Public health protection
Minimizing Nitrification
- Summary ! Monitor water quality
! Limit growth conditions by controlling free
ammonia
! Shock or flush system periodically to remove
bioaccumulation
Acronyms
! AOB - Ammonia-oxidizing bacteria
! DO - Dissolved oxygen
! DOC - Dissolved organic carbon
! FAA - Free Available Ammonia
! HPC - Heterotrophic plate count
! NH3-N - Ammonia as nitrogen
! NO2- - Nitrite
! NH2Cl - Monochloramine
! TOC - Total organic carbon
! NOB - Nitrite-oxidizing bacteria
! UDF - Unidirectional flushing
Bonus Slides
Applying the Concepts . . .
in a practical way
! What do we need to measure to control the
process?
! Where is the best spot to test for it?
! What results are we looking for?
! What do we do if we don't get them?
What to Measure
! Free chlorine
< To find out how much NH3 to apply
! Free Ammonia
< To find out if we applied too much NH3
! Monochloramine (our target disinfectant)
! Total Chlorine
< To find out if we made any di- or trichloramines
Plant Schematic
Cl2
Cl2
Clarifier
Mixer
NH3
Cl2
NH3
Distribution
Clearwell
Where to Measure FAC
Cl2
Cl2
Clarifier
Mixer
FAC
FAC
NH3
Cl2
NH3
Distribution
Clearwell
Where to Measure NH2Cl
Cl2
Cl2
Clarifier
Mixer
NH2Cl
NH3
Cl2
NH2Cl
NH3
Distribution
Clearwell
Where to Measure FAA
Cl2
Cl2
Clarifier
Mixer
FAA
FAA
NH3
FAA
Cl2
NH3
Distribution
Clearwell
Where to Measure TAC
Cl2
Cl2
Clarifier
Mixer
TAC
TAC
NH3
TAC
Cl2
NH3
Distribution
Clearwell
What to Look For
!
!
!
!
!
!
FAC = Target NH2Cl before adding NH3
Little change in FAA after NH2Cl forms
FAA < 0.1 – 0.2 mg/L
NH2Cl at the target
Little change in TAC after NH2Cl forms
TAC = NH2Cl
“When Ratios Go Wrong”
What to Do (Where to Start)
! NH2Cl too high
< Reduce NH3
< Reduce Cl2
• FAA too high
– Reduce NH3
– Increase Cl2
IT'S A BALANCING ACT
• TAC dropped after
NH3 addition
– Increase NH3
– Reduce Cl2
•
TAC > NH2Cl
– Reduce Cl2
Sources of Ammonia (NH3)
! Anhydrous ammonia
< NH3(g)
! Ammonium hydroxide
< NH4OH
! Liquid ammonium sulfate (LAS)
< (NH4)2SO4
Anhydrous NH3
! Description
< Gaseous form compressed into liquid.
< Least expensive form of NH3.
< Most commonly used.
! Storage
< Never store Cl2 gas and NH3 gas in same
room -potential formation of NCl3 (toxic).
< TCEQ requires that anhydrous NH3 systems
be housed and fed in separate enclosure from
Cl2 system.
Anhydrous NH3 - Feeders
! Feeders
< Direct feed
– NH3 injected directly to the water stream
– Not common in Texas
– Used for low-pressure water streams, low
NH3 feed rates
< Solution feed
– NH3 mixed with dilution water prior to
injection to water stream
– Most common method in Texas
– Used for high-pressure water streams, high
NH3 feed rates
Anhydrous NH3 - Safety
! Adequate ventilation should be provided in storage
facilities.
– Forced-air ventilation must be installed.
– The switch for ventilation should be located
outside enclosure so that ventilation can be turned
on prior to entering the enclosure.
– A ventilator must operate under positive pressure.
– Intake fan draws air into bottom of
enclosure.
– NH3 discharged through high-level vent
(unless containment / treatment desired).
< NH3 gas is lighter than air and will accumulate
near the ceiling.
Anhydrous NH3 - Safety
! Safety equipment:
< Safety shower and eye wash fountain
< Industrial gas mask
< One-piece rubber or neoprene suits
< Rescue harness
< High-pressure water system with fog nozzles
< Vapor detection units at high points in storage
and feeder areas
Ammonium Hydroxide (NH4OH)
! Description
< Formed by reaction of NH3 with water.
< NH3 + H2O 6 NH4OH
< Sold as 29-30% NH3 mixtures.
! Storage
< Corrosive to some materials (i.e., copper,
galvanized surfaces).
< Usually stored in steel or fiberglass tanks.
< Should be kept cool due to low boiling point.
< The NH3 vapors that form at high
temperatures should be controlled.
Ammonia Hydroxide (NH4OH)
! Feeders
< Direct feed of NH4OH to water stream
< Stainless steel diffusers with backpressure
! Safety
< Safer than anhydrous NH3 since use of
pressurized container not required
< NH3 vapors that form above NH4OH are
potent
– Adequate ventilation must be provided
– Vapor detection units located at high points
in storage area
Liquid Ammonium Sulfate (LAS)
! Description
< (NH4)2SO4
! Storage
< Corrosive
< Storage equipment and feed systems should
be resistant to H2SO4
< Should not be stored near reactive chemicals
(i.e., Cl2 or lime) or sources of heat
Lime
LAS
LAS
! Feeders
< Direct feed of LAS to water stream
< Design similar to NH4OH
< Diffuser with backpressure
! Operation and maintenance
< Control of corrosion and scaling, as necessary
! Safety
< NH3 gas can be emitted from LAS.
< Provide sufficient ventilation.
< Safety equipment (i.e., goggles) should be
used when handling LAS
Sequence of Injection
! Prechlorination (adding Cl2 before NH3)
< Achieves a free chlorine residual, which results
in:
– Increased disinfection (esp. viruses) compared
to preformed chloramines.
– Removal of color, taste and odors.
– Potential for DBP formation.
< Most common method of chloramine production.
! TCEQ requires that Cl2 (or ClO2, O 3) be used
upstream of NH3 to get any viral inactivation credit
for chloramine.
Sequence of Injection
! Preammoniation
< NH3 added before NH3
< Reduces DBP formation, but also disinfection
capability, removal of color, taste, and odor
< Not allowed by TCEQ unless another disinfectant is
applied prior to NH3.
! Concurrent addition
< Add NH3 and Cl2 at same time.
< DBP formation lower than prechlorination
< Disinfection capability higher than
preammoniation
< Not allowed by TCEQ unless another
disinfectant is applied prior to NH3
Sequence of Injection
! Preformed chloramines
< Mix NH3 and Cl2 in separate tank prior to
addition to water stream.
< NH2Cl solutions degrade with time and
are difficult to preserve.
< This method can result in higher
concentrations of NCl3.
< As a result, the use of preformed
chloramines is not common.
Sequence of Injection
! Systems who use ammonia MUST inject a
strong oxidizer (usually chlorine)
UPSTREAM from the ammonia.
< Chlorine, chlorine dioxide, ozone
! Per EPA rule (footnote in table in guidance)
! There is no TCEQ minimum distance
between injection points
Sequence of Injection
! SWTPs who inject ammonia into raw water
< Should switch immediately to correct
sequence.
< Get no inactivation credit for
chloramine on their SWMORs during
the time when ammonia was fed first.
< Must resubmit SWMORs and get
violations
For More Info, Contact:
Debra Cerda, DWQ Team
Dcerda@tceq.state.tx.us
(512) 239-6045
Amanda Jigmond, TROT Team
Ajigmond@tceq.state.tx.us
(512) 239-6006
Marlo Berg, TROT Team
(512) 239-6967
Mberg@tceq.state.tx.us