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Redondo Beach, California
Feb 27th, 2018
Vacuum UV Photolysis of Nitrate-containing water and the Effect of
Water Matrix on Formation of NitriteMengqi(Maggie) Han, Dr. Madjid Mohseni
Department of Chemical and Biological Engineering
University of British Columbia
Micropollutants in surface water
• Micropollutants are the organic or mineral substances whose toxic, persistent and bio-accumulative properties may have a negative effect on the environment and/or organisms.
• They are present in many products that we consume daily. (drugs, cosmetics, textiles, electronics, pesticides etc.)
http://www.cipel.org/wp-content/uploads/2014/04/Eaudyssee_promo_courriel.jpg
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𝐻2𝑂ℎ𝑣∙ 𝑂𝐻 +∙ 𝐻 ∅ = 0.33
𝐻2𝑂ℎ𝑣∙ 𝑂𝐻 + 𝐻+ + 𝑒𝑎𝑞
− ∅ = 0.045
(2014. AOP chapter, KG.Linden & M.Mohseni)
Two primary reactions:
• A simple approach
• Highly effective for the degradation of most pollutants
• Chemical/Oxidant free
• No generation of solid residuals
Pros of VUV:
H e
VUV lamp
H2O
H
H ee
3
Vacuum UV – 185nm radiation
Challenge: nitrite formation
The UV visible absorption spectra of NO3- and NO2
- (1999. J. Bolton)
VUV: faster formation of nitrite caused by sharp increased absorption spectra of 𝑵𝑶𝟑
−, 𝑵𝑶𝟐
−,
when λ < 250 nm
• Methemoglobinemia (blue baby syndrome)
• A possibility of forming nitrosamine which is known to cause cancer.
• Canadian drinking water guideline set a MCL for NO3
−-N at 10 mg/L and NO2
−-N at 1 mg/L
Health concern
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Possible pathway of nitrate to nitrite
𝑁𝑂3−
𝑒𝑎𝑞−
∙ 𝐻
∙ 𝑂𝐻
(𝑁𝑂3∙)2−
𝑁𝑂3𝐻 ∙−
𝑁𝑂3 ∙
𝑂2
𝐻2𝑂𝑁𝑂2 ∙
𝑁2𝑂3
𝑁2𝑂4
𝑁𝑂2−
𝑂𝑁𝑂𝑂∙
𝑁2𝑂3𝑁𝑂2
−𝑂𝑁𝑂𝑂−
𝑁𝑂 ∙
∙ 𝑂𝐻
[𝑁𝑂3−]∗𝑁𝑂3
−
𝑁𝑂3− [𝑁𝑂3
−]∗ 𝑁𝑂2−
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1.
2.
3.
How to control nitrite formation?
• The factors that effect on nitrite formation:
Lamp type
Wavelength
UV dose
Water condition
Initial nitrate concentration
Water matrix
Temperature
pH
6
Water matrix
Water matrix
Dissolved Organic
Carbon (DOC)
Dissolved Inorganic
Carbon (DIC)Sulfate
Chloride
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DIC: NaHCO3
Nitrate : 10ppm
NaNO3-N
DOC: SRNOM
DIC 0ppm 2ppm 4ppm 6ppm
0ppm ✓ ✓ ✓ ✓
4ppm ✓ ✓
12ppm ✓ ✓ ✓ ✓
48ppm ✓ ✓
Experimental design
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DOC
Methodology
PH adjustmentAlkalinity
determinationDOC
measurementAbsorbance
measurement
Ion concentration
detection
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Experimental setup
1. Copper ballast2. Aluminum lamp housing3. Low pressure mercury lamp4. Nitrogen gas ports5. Teflon collimation tube6. Shutter7. Spectrosil quartz cell plated in
a copper made cuvette holder8. Magnetic stir plate9. Laboratory jack stand
1
23
44
5
67
8
9
10
The effect of DOC and DIC on nitrite formation
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0
0.5
1
1.5
2
2.5
3
0 300 600 900 1200 1500 1800
nit
rite
co
nce
ntr
atio
n(p
pm
)
UV dose(mJ/cm2)
DOC effect
N10 N10 DOC2 N10 DOC4 N10 DOC6
➢ 𝐶𝑁𝑂2− increases with the
increasing of 𝐶𝐷𝑂𝐶. ➢ DOC as strong OH radical
scavenger can compete with 𝑁𝑂2
−.
𝐻𝑂•
NOM
𝑁𝑂2− 𝑁𝑂2
•
[NOM]*
k = 1.0 × 1010 M−1s−1
12
0
0.5
1
1.5
2
2.5
3
0 400 800 1200 1600
nit
rite
co
nce
ntr
atio
n(p
pm
)
UV dose(mJ/cm2)
DOC effect with 2mM TBA
N10 N10 DOC2 N10 DOC4 N10 DOC6
Water matrixExperimental rate constant (ppm/min)
DOC DOC with 2mM TBA
N10 1.0 × 10−2 2.4 × 10−2
N10 DOC2 1.8 × 10−2 2.7 × 10−2
N10 DOC4 2.1 × 10−2 2.7 × 10−2
N10 DOC6 2.4 × 10−2 2.7 × 10−2
➢ Tert-butanol (TBA) as OH radical scavenger, can increase the formation of nitrite.
13
0
0.2
0.4
0.6
0.8
1
1.2
0 300 600 900 1200 1500 1800
Nit
rite
co
nce
ntr
atio
n (
pp
m)
UV dose (mJ/cm2)
DIC effect
N10 N10 DIC4 N10 DIC12 N10 DIC48
1. The low concentration of DIC shows insignificant effect on nitrite formation.
2. 𝐶𝑁𝑂2− is decreased at high
concentration of DIC.
𝑂𝑁𝑂𝑂−
𝑂𝑁𝑂𝑂𝐶𝑂2−
𝐶𝑂2(𝑎𝑞)
N𝑂3−
48%N𝑂2
−Several step
➢ The increased CO2(aq) can react with peroxynitrite (OONO-), which acts as a precursor of nitrite, finally form OONOCO2
and nitrite concentration can be reduced.
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0
0.5
1
1.5
2
2.5
0 400 800 1200 1600
nit
rite
co
nce
ntr
atio
n(p
pm
)
UV dose (mJ/cm2)
DIC effect with 2mM TBA
N10 TBA2mM N10 DIC4 TBA2mM
N10 DIC12 TBA2mM N10 DIC48 TBA2mM
➢ TBA as OH radical scavenger can increase 𝐶𝑁𝑂2−.
➢ However, the effect of DIC as OH radical scavenger is insignificant.
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Water matrixExperimental rate constant (ppm/min)
DIC DIC with 2mM TBA
N10 1.0 × 10−2 2.4 × 10−2
N10 DIC4 1.0 × 10−2 2.3 × 10−2
N10 DIC12 1.1 × 10−2 2.3 × 10−2
N10 DIC48 0.8 × 10−2 1.8 × 10−2
0
0.5
1
1.5
2
2.5
3
0 200 400 600 800 1000 1200 1400
Nit
rite
co
nce
ntr
atio
n(p
pm
)
UV dose(mJ/cm2)
DIC effect with DOC6ppm
N10 DOC6 N10 DOC6 DIC4 N10 DOC6 DIC12 N10 DOC6 DIC48
Water matrixExperimental rate constant (ppm/min)
DIC DIC with 6ppm DOC
N10 1.0 × 10−2 2.4 × 10−2
N10 DIC4 1.0 × 10−2 2.6 × 10−2
N10 DIC12 1.1 × 10−2 2.6 × 10−2
N10 DIC48 0.8 × 10−2 2.5 × 10−2
➢ In DOC contained water, 𝐶𝑁𝑂2− has no
changes with DIC increase.
➢ In both DOC and DIC contained water, DOC effect will be dominant on nitrite formation.
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Conclusion
DOC
Lead to more nitrite formation
𝐶𝑁𝑂2− will increase with the increase of 𝐶𝐷𝑂𝐶
DIC
Insignificant effect on 𝐶𝑁𝑂2−
𝐶𝑁𝑂2− will decrease only at high DIC concentration
DOC&DIC
DOC will be the dominant factor/parameter on nitrite formation
The effect of DIC at high concentration becomes insignificant
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Acknowledgement
• Dr. Mohseni
• Research group members
• RES’EAU WaterNET and all the partners
• NSERC