Mitigating Nitrous Oxide Emission – How to Achieve?

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 • N2O is reported as a green house gas with radiative efficiency about 300 times as high as that of CO2. (IPCC, 2005) • Indicator for nitrification failure • N2O increases (from 16.5 to 186.3 ppm) before the failure of nitrification. (NH3 increases from 3.4 to 41.2 mg/L) (Butler et al., 2008)

3. Nitrogen Cycle • Nitrogen fixation • Aerobic ammoniumoxidation • Aerobic nitrite oxidation • Denitrification • Anaerobic ammonium oxidation • Anaerobic dissimilatory nitrate and nitrite reduction

4. AMO HAO NXR NH3 NH2OH NO2- NO3- Enzymes Required for Nitrification • Oxidation of NH3 to NO3- -120kJ mol-1 -114kJ mol-1 -74kJ mol-1 AMO : Ammonia monooxygenase HAO : Hydroxylamine oxidoreductase NXR : Nitrite oxidoreductase (NOR in old papers!)

5. NO3- NO2- NO N2O N2 NAR NIR NOR NOS Enzymes Required for Denitrification • Reduction of NO3- to N2 2 types 3 types 1 or ??? NAR : Nitrate reductase NIR : Nitrite reductase NOR : Nitric oxide reductase NOS : Nitrous oxide reductase

6. ??? Anammox • Anammox : Anaerobic Ammonium Oxidation • NH4+ + NO2- N2 + H2O • 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 bc1: cytochrome bc1 complex (Kuenen, 2008)

8. AMO HAO NH3 NH2OH NO2- N2O NOR NO N2O Source of Nitrous Oxide • Nitrification • Byproducts of hydroxylamine oxidation or ammonia to hydroxylamine pathway • Denitrification • Obligatory intermediates

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 N2O 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 NO3- to N2O rather than to N2. (Liu et al., 2008)

11. Operations to Affect N2O 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: Paracoccusdenitrificans, Alcaligenes faecalis, Pseudomonas putida • Anaerobic Nitrification (Anammox) • Anammox bacteria

13. 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/LO2 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% O2 by 27%. (Su et al., 2004) Bacterial Community Not all bacterial species are capableto produce nitrous oxide reductase (NOS) !

14. Conclusion • In order to mitigate N2O 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?