Mitigating Nitrous Oxide Emission – How to Achieve? Environmental Seminar 08/03/2009 Cheng-Yao Tsai University of California, Irvine
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 ppm) before the failure of nitrification. (NH 3 increases from 3.4 to 41.2 mg/L) (Butler et al., 2008)
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
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 kJ mol kJ mol -1
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 ???
Anammox Anammox : Anaerobic Ammonium Oxidation NH NO 2 - N 2 + H 2 O Species: Brocadia anammoxidans Kuenenia stuttgartiensis “ Candidatus ” Scalindua brodae “ Candidatus ” Scalindua wagneri “ Candidatus ” Scalindua sorokinii ???
Mechanisms of Anammox HH: Hydrazine hydrolase HAO: Hydrazine oxidoreductase HD: Hydrazine dehydrogenase Q: Quinone bc 1 : cytochrome bc 1 complex (Kuenen, 2008)
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
Respiratory of Nitrous Oxide Nitrous Oxide Reductase (NOS)
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)
Operations to Affect N 2 O Emission Oxygen concentration C/N ratio Ammonia loading rate Hydraulic retention time (Hwang et al., 2006)
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
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) !
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?
Thanks for your listening! Questions?