Disinfectant Residual Stability
Issues and Possible Control
Strategies in Desalinated
Seawater
Yan Zhang,
g Tai J. Tseng,
g Cynthia
y
Andrews-Tate, Robert
AndrewsC. Cheng, Kevin L. Wattier
DXV Water Technologies, LLC
L
Long
Beach
B
h Water
W t Department
D
t
t
1
Long Beach Water Department
• California’s 6th most p
populous
p
city
y
•
•
•
•
•
(~500,000 residents)
70,000
,
AF/yr
y of drinking
g water
8,000 AF/yr of reclaimed water
Operate
p
largest
g
GW treatment p
plant in US
900+ miles of drinking water lines
750+ miles of sewer lines
2
LBWD’s Resource Mix
2010
2015
Conservation
15%
Groundwater
44%
Reclaimed
R
l i d
9%
Imports
32%
Desal
Conservation
ti
10% C
15%
Groundwater
33%
Reclaimed
12%
Imports
%
30%
3
LBWD’s Desalination Program
z A $20 M, 1010-year investment
z Leverage various partnerships for technical input and other support
z Federal/State/Local Funds
Pretreatment
•Under Ocean Floor Intake and
Discharge
NF2 or RO
•Prototype
•UV/ClO
UV/ClO2
Post treatment / Distribution
•Mitigation of WQ impacts due to
i t
integration
ti off new source
4
Predicted Impacts of Desalinated Water
on Disinfectant Residual Stability
6 Raw seawater has bromide 6565-67 mg/L (mean
level in US drinking water source is 63 µg/L)
6 High bromide is predicted to decrease
disinfectant (chloramine) stability, mechanism not
well understood
HOCl + NH3 Æ NH2Cl
HOCl + Br- Æ HOBr
HOBr + NH3 Æ NH2Br
Catalyst??? Br-
NH3
Possible Control Strategies
6 Reduce bromide levels in permeate
ƒ What
Wh t bromide
b
id llevell iis acceptable?
t bl ?
6 Reboost residual after initial decay
6 Changing disinfection practice
ƒ Switch to chlorine
ƒ Preforming chloramine before contacting with
permeate
HOCl + NH3 Æ NH2Cl
HOCl + Br- Æ HOBr
HOBr + NH3 Æ NH2Br
Catalyst???
BrNH3
Research Objectives
6 Establish a critical bromide level in permeate
water
t where
h
chloramine
hl
i stability
t bilit iis nott
impacted
6 Evaluate other options (e.g., preforming
chloramine and reboosting chlorine) for
situations where low bromide levels can not
be achieved economically
Overall Objective-establish feasible
control
t l strategies
t t i
7
Research Approach
6 Base waterwater-permeate water from desalination
Prototype
yp Plant
6 Bench scale testing
ƒ 100% permeate water, 4 mg/L target chloramine dose
ƒ Monitor
M it chloramine
hl
i d
decay vs. diff
differentt b
bromide
id llevels
l
ƒ Testing effectiveness of other control strategies: preforming
chloramine and reboosting chlorine
6 Demonstration scale pipe loop testing
ƒ 50:50 blending of permeate and existing distribution system
water ((DSW),
), 22-2.5 mg/L
g target
g dose
ƒ Monitor chloramine decay in different pipe materials (iron,
copper, cement lined pipes, etc) after 8 hour target stagnation
time
ƒ Compare decay in DSW and blending water
8
Bromide Levels in Testing Water
Prototype Plant
Pipe Loop Testing
6 Bromide in permeate: 0.140.14-3.68 ppm
6 Bromide in pipe loops: 30 – 900 ppb
9
Critical Bromide Levels
-Bench Scale
S
Testing
10
5
chlora
amine resid
dual, mg/L
L
4.5
4
3.5
3
150 ppb bromide
25
2.5
250 ppb bromide
2
450 ppb bromide
1.5
750 ppbb bbromide
id
1150 ppb bromide
1
0
4
8
12
16
20
24
Time, hour
11
5.5
chloraamine resid
dual, mg/L
5
4.5
4
3.5
3
150 ppb bromide
2.5
250 ppb bromide
2
450 ppb bromide
750 ppb bromide
1.5
1150 ppb bromide
1
0
4
8
12
16
20
24
Time, hour
12
4.5
chloram
mine residu
ual, mg/L
4
3.5
3
2.5
150 ppb bromide
2
250 ppb bromide
450 ppb bromide
1.5
750 ppb bromide
1150 ppb bromide
1
0
4
8
12
16
20
24
Time, hour
13
6 Bromide ≤ 250 ppb: ≤ 11% chloramine
decayed after 8 hours
6 Bromide
B
id = 450 ppb:
b ≤ 22% chloramine
hl
i
decayed after 8 hours
6 Bromide ≥ 750 ppb: > 30% chloramine
decayed after 8 hours
14
Critical Bromide Levels
-Pipe Loop Testing
6 Bromide had no impact
p
on chloramine decay
y in
cast iron and copper pipes
ƒ Iron and copper species dominated decay
15
Chloramine Residual with Blend Water after
8 hour Stagnation
Chloram
mine resid
dual, mg/L
L
3.5
3
2.5
2
Influent
Chloramine
1.75
1.5
1
0.86
0.89
05
0.5
0
Iron
Copper
Cement lined ductile
n=110
n=112
n=113
16
Critical Bromide Levels
-Pipe Loop Testing
6 Bromide had no impact
p
on chloramine decay
y in
cast iron and copper pipes
ƒ Iron and copper species dominated decay
6 Bromide impact on chloramine decay in cement
lined (CML) pipes depends on the level
17
Chloramine Residual with Blend Water in
Cement Lined Pipes after 8 hour Stagnation
3
C
Chloramin
e residuall, mg/L
25
2.5
Influent
Chloramine
2
1.5
1
0.5
0
0
200
400
600
Bromide, ppb
800
1000
18
Chloramine Residual with Blend Water in
Cement Lined Pipes after 8 hour Stagnation
3
Chloramine residual
chloramine residual (without DSW decay)
C
Chloramine
e residual, mg/L
25
2.5
Influent
Chloramine
2
1.5
1
Minimum
Decay
0.5
Medium
Decay
0
0
200
400
600
Bromide, ppb
800
1000
19
Chloramine Residual Water in Cement
Lined Pipes after 8 hour Stagnation
2.5
∆ decay by DSW
∆ decay by blend water
∆C
Chloramin
ne decay, mg/L
2
Minimum Medium
Decay
Decay
1.5
5
1
0.5
0
0
200
400
600
800
1000
-0.5
Bromide, ppb
20
In 50:50 blend water:
6 Bromide ≤ 300
300--350 ppb had very minimum
decay (residual > 2 mg/L after 8 hour)
6 Bromide
B
id 350
350--500 ppb
bh
had
d medium
di
llevell off
decay (residual 1.51.5-2 mg/L after 8 hour)
Bromide < 1 mg/L in permeate
is operationally acceptable for
50:50 blending situation
21
Other Control Strategies
g
6 Preformingg chloramine
6 Reboosting Chlorine after initial decay
22
chlorramine res
sidual, mg
g/L
45
4.5
4
3.5
chlorine + ammonia, 0.8
mg/L Bromide
3
pref ormed chloramine, 0.8
mg/L Bromide
2.5
chlorine + ammonia,, 1.2
mg/L Bromide
2
0
8
16
24
32
40
48
Time, hour
23
4.5
chloramin
ne residua
al, mg/L
4
chlorine + ammonia,
0.9 mg/L Bromide
pref ormed chloramine,
0.9 mg/L Bromide
chlorine + ammonia,
2.7 mg/L Bromide
3.5
3
2.5
2
1.5
0
8
16
24
Time, hour
32
40
48
24
6 When bromide ≤ 1.2 mg/L: preforming
chloramine and reboosting were effective in
maintaining residual
6 When bromide = 2.7 mg/L: reboosting was
not effective
25
Conclusions
6 What’s an acceptable bromide level?
ƒ < 300 ppb: minimum decay
ƒ 300
300--500 ppb: medium decay
ƒ >500 ppb: strong decay
6 Other strategies work?
ƒ Preforming
P f
i and
d reboosting
b
ti were effective
ff ti when
h
bromide < 1.2 mg/L
ƒ At extremely high bromide level (2
(2.7
7 mg/L)
mg/L),
reboosting not effective
26
Acknowledgement
6 Fundingg ppartners:
ƒ US Bureau of Reclamation
ƒ CA Dept
p of Water Resources
ƒ Los Angeles Dept of Water and Power
6 LBWD WQ Lab and treatment pplant staff
27