vuv photolysis of nitrate and formation of nitrite › resources › 2018_iuva_americas_conference...

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

2

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

4

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−

5

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

7

DIC: NaHCO3

Nitrate : 10ppm

NaNO3-N

DOC: SRNOM

DIC 0ppm 2ppm 4ppm 6ppm

0ppm ✓ ✓ ✓ ✓

4ppm ✓ ✓

12ppm ✓ ✓ ✓ ✓

48ppm ✓ ✓

Experimental design

8

DOC

Methodology

PH adjustmentAlkalinity

determinationDOC

measurementAbsorbance

measurement

Ion concentration

detection

9

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

11

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.

14

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.

15

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.

16

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

17

Acknowledgement

• Dr. Mohseni

• Research group members

• RES’EAU WaterNET and all the partners

• NSERC