Vacuum UV Photolysis of Nitratecontaining water and the Effect of Water Matrix on Formation of Nitrite

Transcription

1 Vacuum UV Photolysis of Nitratecontaining water and the Effect of Water Matrix on Formation of Nitrite Mengqi(Maggie) Han, Dr. Madjid Mohseni Department of Chemical and Biological Engineering University of British Columbia Redondo Beach, California Feb 27 th, 2018

2 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.) 2

3 Vacuum UV 185nm radiation VUV lamp Pros of VUV: H e e H H H 2 O e A simple approach Highly effective for the degradation of most pollutants Chemical/Oxidant free No generation of solid residuals Two primary reactions: H 2 O hv OH + H = 0.33 H 2 O hv OH + H + + e aq = (2014. AOP chapter, KG.Linden & M.Mohseni) 3

4 Health concern Challenge: nitrite formation Methemoglobinemia (blue baby syndrome) A possibility of forming nitrosamine which is known to cause cancer. Canadian drinking water guideline set a MCL for NO 3 -N at 10 mg/l and NO 2 -N at 1 mg/l VUV: faster formation of nitrite caused by sharp increased absorption spectra of NO 3, NO2, when λ < 250 nm The UV visible absorption spectra of NO 3- and NO 2 - (1999. J. Bolton) 4

5 Possible pathway of nitrate to nitrite 1. NO 3 e aq OH H (NO 3 ) 2 NO 3 H NO 3 O 2 H 2 O NO NO 2 N 2 O 3 NO 2 N 2 O 4 2. NO 3 [NO 3 ] ONOO N 2 O 3 NO 2 OH ONOO 3. NO 3 [NO 3 ] NO 2 5

6 How to control nitrite formation? The factors that effect on nitrite formation: Lamp type Water condition Wavelength Initial nitrate concentration UV dose Water matrix Temperature ph 6

7 Water matrix Dissolved Inorganic Carbon (DIC) Sulfate Dissolved Organic Carbon (DOC) Water matrix Chloride 7

8 Experimental design Nitrate : 10ppm NaNO 3 -N DOC: SRNOM DIC: NaHCO 3 DOC DIC 0ppm 2ppm 4ppm 6ppm 0ppm 4ppm 12ppm 48ppm 8

9 Methodology PH adjustment Alkalinity determination DOC measurement Absorbance measurement Ion concentration detection 9

10 Experimental setup Copper ballast 2. Aluminum lamp housing 3. Low pressure mercury lamp 4. Nitrogen gas ports 5. Teflon collimation tube 6. Shutter 7. Spectrosil quartz cell plated in a copper made cuvette holder 8. Magnetic stir plate 9. Laboratory jack stand 10

11 The effect of DOC and DIC on nitrite formation 11

12 nitrite concentration(ppm) 3 DOC effect N10 N10 DOC2 N10 DOC4 N10 DOC UV dose(mj/cm 2 ) C NO2 increases with the increasing of C DOC. DOC as strong OH radical scavenger can compete with NO 2. NOM [NOM]* HO k = M 1 s 1 NO 2 NO 2 12

13 nitrite concentration(ppm) DOC effect with 2mM TBA N10 N10 DOC2 N10 DOC4 N10 DOC Tert-butanol (TBA) as OH radical scavenger, can increase the formation of nitrite Water matrix Experimental rate constant (ppm/min) UV dose(mj/cm 2 ) DOC DOC with 2mM TBA N N10 DOC N10 DOC N10 DOC

14 Nitrite concentration (ppm) DIC effect N10 N10 DIC4 N10 DIC12 N10 DIC The low concentration of DIC shows insignificant effect on nitrite formation. 2. C NO2 is decreased at high concentration of DIC The increased CO 2(aq) can react with peroxynitrite (OONO - ), which acts as a precursor of nitrite, finally form OONOCO 2 and nitrite concentration can be reduced UV dose (mj/cm 2 ) NO 48% Several step ONOO 3 NO 2 CO 2(aq) ONOOCO 2 14

15 nitrite concentration(ppm) DIC effect with 2mM TBA N10 TBA2mM N10 DIC12 TBA2mM N10 DIC4 TBA2mM N10 DIC48 TBA2mM TBA as OH radical scavenger can increase C NO2. However, the effect of DIC as OH radical scavenger is insignificant Water matrix Experimental UV dose (mj/cm 2 ) rate constant (ppm/min) DIC N N10 DIC N10 DIC N10 DIC DIC with 2mM TBA 15

16 Nitrite concentration(ppm) N10 DOC6 N10 DOC6 DIC4 N10 DOC6 DIC12 N10 DOC6 DIC DIC effect with DOC6ppm In DOC contained water, C NO2 has no changes with DIC increase. In both DOC and DIC contained water, DOC effect will be dominant on nitrite formation UV dose(mj/cm 2 ) Experimental rate constant (ppm/min) Water matrix DIC N N10 DIC N10 DIC N10 DIC DIC with 6ppm DOC 16

17 Conclusion DOC Lead to more nitrite formation C NO2 will increase with the increase of C DOC DIC DOC&DIC Insignificant effect on C NO2 C NO2 will decrease only at high DIC concentration DOC will be the dominant factor/parameter on nitrite formation The effect of DIC at high concentration becomes insignificant 17

18 Acknowledgement Dr. Mohseni Research group members RES EAU WaterNET and all the partners NSERC

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