1. Mitigating Nitrous Oxide Emission – How to Achieve? Environmental Seminar 08/03/2009 Cheng-Yao Tsai University of California, Irvine

2. Motivation Green house gas emission concern N 2 O is reported as a green house gas with radiative efficiency about 300 times as high as that of CO 2. (IPCC, 2005) Indicator for nitrification failure N 2 O increases (from 16.5 to 186.3 ppm) before the failure of nitrification. (NH 3 increases from 3.4 to 41.2 mg/L) (Butler et al., 2008)

3. Nitrogen Cycle 1.Nitrogen fixation 2.Aerobic ammonium oxidation 3.Aerobic nitrite oxidation 4.Denitrification 5.Anaerobic ammonium oxidation 6.Anaerobic dissimilatory nitrate and nitrite reduction

4. Enzymes Required for Nitrification  Oxidation of NH 3 to NO 3 - NH 3 NH 2 OH NO 2 - NO 3 - HAOAMONXR AMO : Ammonia monooxygenase HAO : Hydroxylamine oxidoreductase NXR : Nitrite oxidoreductase (NOR in old papers!) -120kJ mol -1 -114kJ mol -1 -74kJ mol -1

5. Enzymes Required for Denitrification  Reduction of NO 3 - to N 2 NO 3 - NO 2 - NO N 2 O N 2 NARNIRNORNOS NAR : Nitrate reductaseNIR : Nitrite reductase NOR : Nitric oxide reductaseNOS : Nitrous oxide reductase 2 types3 types1 or ???

6. Anammox  Anammox : Anaerobic Ammonium Oxidation NH 4 + + NO 2 - N 2 + H 2 O Species:  Brocadia anammoxidans  Kuenenia stuttgartiensis  “ Candidatus ” Scalindua brodae  “ Candidatus ” Scalindua wagneri  “ Candidatus ” Scalindua sorokinii ???

7. Mechanisms of Anammox HH: Hydrazine hydrolase HAO: Hydrazine oxidoreductase HD: Hydrazine dehydrogenase Q: Quinone bc 1 : cytochrome bc 1 complex (Kuenen, 2008)

8. Source of Nitrous Oxide  Nitrification Byproducts of hydroxylamine oxidation or ammonia to hydroxylamine pathway  Denitrification Obligatory intermediates NH 3 NH 2 OH NO 2 - HAOAMO N2ON2O NO N 2 O NOR

9. Respiratory of Nitrous Oxide  Nitrous Oxide Reductase (NOS)

10. Environmental Factors on NOS  Adequate supply of copper. 1µM copper is required at least for N 2 O reduction. (Matsubara et al., 1982) 1.6mM to 2.0mM will poison pseudomonas syringae. (Trevors and Cotter, 1990)  NOS is sensitive to pH. pH<7 is soils drives the reduction of NO 3 - to N 2 O rather than to N 2. (Liu et al., 2008)

11. Operations to Affect N 2 O Emission  Oxygen concentration  C/N ratio  Ammonia loading rate  Hydraulic retention time (Hwang et al., 2006)

12. Bacterial Community  Aerobic Nitrification Autotroph: Ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) e.g. Nitrosomonas, Nitrosospira (AOB), Nitrobactor (NOB). Heterotroph: Paracoccus denitrificans, Alcaligenes faecalis, Pseudomonas putida  Anaerobic Nitrification (Anammox) Anammox bacteria

13. Bacterial Community  Denitrification Autotroph: AOB (cell maintenance-no growth) Heterotroph: Bacillus, Pseudomonas, Sprillum, Alcaligenes, Agrobacterium … and so on. Some are aerobic denitrifiers!  Pseudomonas putida can tolerate 5-6 mg/L O 2 and perform nitrate removal rate as high as 95.9%. (254.6 mg/L hour) (Kim et al., 2008)  Paracoccus denitrificans reduced added nitrate in an atmosphere of 92% O 2 by 27%. (Su et al., 2004) Not all bacterial species are capable to produce nitrous oxide reductase (NOS) !

14. Conclusion  In order to mitigate N 2 O production from wastewater treatment process, pH>7 Longer HRT (above 2 days) Adequate ammonia loading rate Carbon and copper supply Oxygen condition in anoxic zone (<80µM)  New operation system?

15. Thanks for your listening! Questions?