Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves [135]-139). Also available on the Internet.

Reproduction de : Thèse de doctorat : Chimie organique, minérale et industrielle : Poitiers : 2008. / Titre provenant de l'écran-titre. Bibliogr. 239 réf.

Thèse de doctorat : Géosciences : Nancy 1 : 2009. / Titre provenant de l'écran-titre.

Includes bibliographical references (p. 62-73).

Nitrifier denitrification is a poorly quantified microbial process leading to emissions of N2O from soils. Nitrous oxide emissions, particularly from agricultural soils, are currently being targeted for reduction due to the contribution of this gas to anthropogenic climate change. Measurements specific to nitrifier-denitrification are hampered by poor culturability of many of the strains involved, and the inability of single isotope labelling methods to distinguish it from denitrification carried out by other organisms, dual-labelling approaches and evidence form pure cultures suggest that its contribution to nitrous oxide emissions may be large. Environmental conditions favouring the pathway are unknown, leading to difficulties in mitigation or modelling. In this thesis data from both dual-labelling isotopic techniques and isotopomer measurements of the nitrous oxide emitted are used to determine whether isotopomer techniques can quantify nitrifier-denitrification in situ, and the conditions under which nitrous oxide emissions from the pathway are increased are investigated. Data is also presented on site preference (isotopomer ratio) from ammonia oxidation in several Nitrosospira strains for which this has previously not been measured. The capacity of Nitrosospira strains in pure culture to reduce N2O to N2, an environmentally neutral product of the nitrogen cycle, are investigated. Site preference results from this research suggest that nitrifier denitrification cannot be distinguished from heterotrophic denitrification by site preference, indicating that previously published data stating proportional outputs of N2O from dentrification may overestimate heterotrophic contributions. Several Nitrosospira strains are found to be capable of a reduction step from N2O to N2 in pure culture conditions. Nitrifier denitrification is found to respond to environmental factors of soil N-level, pH and rainfall events, and changes in site preference also occur under these conditions. Site preference is linked to microbial phylogeny for the strains of Nitrosospira tested, indicating a possible effect of enzyme structure above pathway level determination.

No description available.

In recent years there has been widespread interest in rearing aquatic organisms of nutritional and commercial value (Calaprice, 1976). The most hopeful prospect for marine prawn culture in the United Kingdom (Wickins, 1976), the Americas (Hanson & Goodwin, 1977) and South Africa probably lies in intensive culture under controlled conditions. A closed system approach, in which a captive body of water is circulated, provides the scope for water quality management which results ~n maximum water utilization and minimal discharge. On the other hand, direct utilization of sea-water in open systems presents problems for aquaculture since this water is subjected to diurnal and seasonal fluctuations in temperature, salinity and turbidity, as well as contamination from industrial, agricultural and maritime sources. Furthermore, large mariculture farms release enormous amounts of organic wastes which result in eutrophication and could lead to environmental deterioration of coastal waters (Gerhardt, 1978). It is well established that circulated sea-water develops an unusual ~on~c composition as a result of the metabolic activity of the prawns and of the nitrifying bacteria in the biological filter. The changes include elevated levels of ammonia, nitrite and nitrate and reduced pH. The presence of even sublethal levels of these nitrogenous compounds ~n closed systems have been found to affect growth of penaeid spec~es (Wickins, 1976). Ammonia and nitrite, which rapidly accumulate in the water, are usually maintained at nontoxic levels by nitrification in the biological filters (Spotte, 1974; Johnson & Sieburth, 1974). The chemolithotrophic bacteria responsible for nitrification are presently classified by their · cellular morphology and by the oxidation of either ammonia and nitrite (Watson, 1974). The predominant ammonia- and nitrite-oxidizing bacteria isolated from natural environments are Nitrosomonas europaea and Nitrobacter winogradskyi, respectively (Watson et aZ., 1981). Direct observation of nitrifying bacteria in natural environments, however, has been limited to studies involving light microscopy with immunofluorescent techniques (Fliermans et aZ., 1974; Fliermans & Schmidt, 1975). The electron microscopic observation of nitrifying bacteria ~sdifficult in natural microcosms with low levels of nitrification and with the presence of sunlight and anaerobic conditions conducive to the enrichment of other bacteria with a similar ultrastructure. However, in closed systems with extremely active nitrification but poor light conditions, the occurrence of morphologically similar forms in numbers that could be easily detected by electron microscopy is unlikely (Johnsort & Sieburth, 1976). Furthermore, the cyst-like colonies of the nitrifiers are unique and are not found with the methane-oxidizing bacteria with a similar ultrastructure (Davies & Whittenbury, 1970; Smith & Ribbons, 1970), whereas the thick cell wall of the cyanobacteria (Carr & Whitton, 1973) and the distinctive cell morphologies of the purple sulphur and purple nonsulphur bacteria (Pfennig, 1967) separate them from the nitrifiers. Therefore, closed systems with active nitrification provide the ideal environment to study the activities of nitrifiers in conjunction with their relative abundance, nature and diversity. In spite of the opportunity offered by closed systems, previous studies (Kawai et aZ., 1965; Wickins, 1976; Gerhardt, 1978; Mevel & Chamroux, 1981) on nitrification have been primarily indirect observations on rates of ammonia and nitrite oxidation to nitrate (Johnson & Sieburth, 1976). Studies on the enumeration and identification of nitrifiers ~n closed systems have been seriously neglected. Kawai et aZ. (1964) included the enumeration of nitrifiers in their study on nitrification while,in a qualitative study, an attempt to identify the in situ nitrifiers 1n closed systems (Johnson & Sieburth, 1976) was not very successful. This study was undertaken to investigate the three basic aspects of nitrification necessary for the understanding of such a process in closed systems, viz., the oxidation of ammonia and nitrite to nitrate, and the enumeration and identification of the nitrifying bacteria. Prior to determining the concentrations of the nitrogenous compounds in the culture water, various methods were evaluated for their accuracy and reproducibility with both sea-water and culture water samples. This approach is necessary in order to gauge the accuracy of results obtained by such methods. Enumeration of nitrifying bacteria was preceded by an investigation on the effect of incubation time on the maximum most probable number , estimate. Such an investigation was necessary because of the inconsistent approach to the enumeration of nitrifiers in previous studies (Wilson, 1927; Walker et al., 1937; Lewis & Pramer, 1958; Molina & Rovira, 1964; Meiklejohn, 1965; Smith et al., 1968). Incubation periods appear to have been chosen arbitrarily in previous investigations. Identifi~ation of nitrifying bacteria necessitates the isolation and purification of these organisms. Isolation of nitrifiers 1S a difficult and time-consuming task (Watson et al., 1981) and could be the main reason for not being included in previous studies on nitrification. Since the success of this study depended upon the isolation and purification of these chemolithotrophs, this aspect is de~lt with in detail. The changes most likely to be associated with nitrification in a closed system were also monitored 1n the culture water. These included pH, dissolved oxygen and biochemical oxygen demand. Apart from a biological sand filter, no other form of culture water treatment was effected during the investigation. The effect of growing the "sugpo" or jumbo tiger prawn, Penaeus monodon (Kinne, 1977) for 22 weeks in a captive body of sea-water was evaluated by comparing the survival and wet mass with those reported by other workers. This study differs greatly from previous reports on nitrification in closed systems because both the "causes" and "symptoms" of this important detoxifying process are investigated. It is intended that the findings of such a study would aid culturists in exploiting the nitrifying potential of closed systems to its utmost. / Thesis (M.Sc.)-University of Durban-Westville, 1984.

The purpose of this thesis was to compare ethinylestradiol (EE2) and nitrogen removal in a conventional membrane bioreactor (C-MBR) and a simultaneous nitrification-denitrification membrane bioreactor (SND-MBR). Two MBRs were operated in parallel for 450 days; various MBR operating parameters, total nitrogen removal, and estrogenic activity removal (EA) were measured. The SND-MBR was able to remove 59% of influent TN with an additional 21% removed via sludge wasting; the C-MBR had a TN removal efficiency of only 31%. The C-MBR and SND-MBR removed 57% and 58% of influent EA, respectively. Biodegradation was the dominant removal mechanism for both reactors with KBIO coefficients of 1.5 ± 0.6 and 1.6 ± 0.4 days-1 for the C-MBR and the SND-MBR, respectively. Adsorption removed approximately 1% of influent EA in each reactor. This indicates that SND was able remove greater amounts of TN with no observable impact on EA reduction and membrane operations.

This study examined the impact of active layer detachments (ALDs) on seasonal dissolved nitrogen (N) export from continuous permafrost headwater catchments at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut. Runoff samples collected throughout the summer of 2012 from an undisturbed catchment (Goose; GS) and from one that was disturbed by ALDs (Ptarmigan; PT) were analyzed for dissolved inorganic ions and species of total dissolved N (TDN), including dissolved organic N (DON) and dissolved inorganic N (DIN; ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-)). Rainfall samples were also collected for dissolved ions analyses. Select runoff and rainfall samples were analyzed for stable isotopes of nitrogen and oxygen in NO3- (δ15N-NO3- and δ18O-NO3-, respectively) to determine its origin streamwater. Data from 2012 were compared to predisturbance data to assess the long-term effects of ALDs on N export. ALDs increased the proportion of DIN/TDN in PT from 4% (predisturbance) to 37% in 2012. The increase in DIN/TDN in PT largely resulted from significantly higher NO3- in runoff. Values of δ18O and δ15N-NO3- as well as correlations between NO3- and major ions indicated that the higher NO3- in PT was due to the exposure of mineral soils in ALDs, which likely reduced NO3- sinks (e.g. plant uptake) and increased inputs of nitrified-NO3-. Values of δ18O-NO3- during initial runoff showed that NO3- supplied from the snowpack overwhelmed NO3- sinks in PT, leading to a twelve-fold higher peak NO3- concentration relative to GS. Low δ18O-NO3- values in runoff during stormflow indicated that inputs of DIN from rainfall (1545 ± 148 and 1838 ± 174 g N-DIN to GS and PT, respectively) supplied less than 30% of the NO3- in both streams, and that exceptionally high NO3- concentrations in PT resulted from flushing of mineralized-NO3- from the mineral soils. Seasonal DIN flux was 95% higher in PT relative to GS, because NO3- export from PT was 27 times that of GS. This is the first study to show that ALDs can have persistent impacts on DIN export from High Arctic watersheds, and that this results from enhanced export of mineralized-NO3-. / Thesis (Master, Geography) -- Queen's University, 2014-05-27 10:30:38.874

The purpose of this thesis was to compare ethinylestradiol (EE2) and nitrogen removal in a conventional membrane bioreactor (C-MBR) and a simultaneous nitrification-denitrification membrane bioreactor (SND-MBR). Two MBRs were operated in parallel for 450 days; various MBR operating parameters, total nitrogen removal, and estrogenic activity removal (EA) were measured. The SND-MBR was able to remove 59% of influent TN with an additional 21% removed via sludge wasting; the C-MBR had a TN removal efficiency of only 31%. The C-MBR and SND-MBR removed 57% and 58% of influent EA, respectively. Biodegradation was the dominant removal mechanism for both reactors with KBIO coefficients of 1.5 ± 0.6 and 1.6 ± 0.4 days-1 for the C-MBR and the SND-MBR, respectively. Adsorption removed approximately 1% of influent EA in each reactor. This indicates that SND was able remove greater amounts of TN with no observable impact on EA reduction and membrane operations.