Denitrification characterization

The technical and economic aspects of wet flue gas simultaneous desulfurization and denitrification systems are presented so that their practicality for utilization by utility industry can be assessed. The emphasis is on the kinetics of the systems based on the employment of ferrous chelates to promote the solubility of NO and the reactivity of NO with SO2 in scrubbing liquors. Analytical techniques are developed for characterizing reaction intermediates and products. Alternative approaches and novel ideas that could develop into a more efficient and cost-effective scrubber system employing metal chelate additives are discussed. 

This chapter focuses on the chemistry ofbiomimetic copper nitrosyl complexes relevant to the NO-copper interactions in proteins that are central players in dissimilatory nitrogen oxide reduction (denitrification). The current state of knowledge of NO-copper interactions in nitrite reductase, a key denitrifying enzyme, is briefly surveyed the syntheses, structures, and reactivity of copper nitrosyl model complexes prepared to date are presented and the insight these model studies provide into the mechanisms of denitrification and the structures of other copper protein nitrosyl intermediates are discussed. Emphasis is placed on analysis of the geometric features, electronic structures, and biomimetic reactivity with NO or NOf of the only structurally characterized copper nitrosyls, a dicopper(II) complex bridged by NO and a mononuclear tris(pyrazolyl)hydroborate complex having a Cu(I)-NO formulation. 

Figure 29.2 Schematic overview of the marine nitrogen cycle. A Important species, their oxidation state (vertical axis), and major biological transformations of nitrogen (arrows). B Typical values of the isotopic enrichment factor (e) are shown for reactions that have been characterized isotopically. Estimates of 6 were drawn from the available literature on N2-fixation and the of diazotrophs (Carpenter et al, 1997 Delwiche and Steyn, 1970 Hoering and Ford, 1960 Macko et al., 1987 Montoya et ah, 2002), denitrification (Barford et ah, 1999 Cline and Kaplan, 1975 Delwiche and Steyn, 1970 Mariotti et ah, 1981,1982 McCready et ah, 1983 Miyake and Wada, 1971 Voss et ah, 2001 Wada, 1980 ), nitrification (Delwiche and Steyn, 1970 Mariotti et ah, 1981 Miyake and Wada, 1971 Ybshida, 1988), N03 uptake (Montoya and McCarthy, 1995 Needoba et ah, 2003 Needoba and Harrison, 2004 Pennock et ah, 1996,1998 Wada and Hattori, 1978 Waser et ah, 1998a, 1998b ), NO2 uptake (Wada and Hattori, 1978 Wada, 1980), NH4 uptake (Cifuentes et ah, 1989 Montoya et ah, 1991 Pennock et ah, 1988 Wada, 1980 Wada and Hattori, 1978), and zooplankton excretion (Checkley and Miller, 1989).

Within the ODZ, nitrous oxide (N20), another major intermediate of denitrification (and a byproduct of nitrification), shows a trend of variability quite different from that of N02 (Fig. 6.15), but similar to that observed in the ODZs of the Pacific Ocean (Codispoti Christensen, 1985). That is, N20 concentration generally increases non-linearly with the depletion in 02 until the environment turns reducing thereafter, concomitant with the accumulation of secondary N02, a rapid fall in N20 concentration takes place. Accordingly, the SNM is characterized by a minimum in N20 concentration (<10nM), whereas the oxic-suboxic interfaces are characterized by peak N20 levels exceeding 50nM (Law Owens, 1990 Naqvi Noronha, 1991). Attempts have been made to evaluate the relative importance of nitrification, denitrification and coupling between the two processes as pathways for N20 production by... 

Nitrous oxide reductases are soluble, periplasmic Cu-containing enzymes encoded by nosZ that catalyze the final step in denitrification (Equation (10)). This reaction is difficult chemistry, since N2O is a poor ligand for transition metals, is kinetically inert, and none of the known metal/N20 complexes have been structurally characterized. No CU/N2O chemistry, other than that associated with N2OR, has been reported ... 

Horiba, Y, Khan, S.T. and Hiraishi, A. (2005) Characterization ofthe microbial community and culturable denitrifying bacteria in a solid-phase denitrification process using poly(-caprolactone) as the carbon and energy source. Microbes and Environments, 20, 25-33. 

---