Nitrous oxide (N2O) is a potent greenhouse gas mainly emitted from agriculture. In the biological process of denitrification, intermediates of the nitrogen cycle are reduced under oxygen limiting conditions thereby releasing N2O. Denitrification is influenced by various environmental factors and both bacteria and fungi are capable of denitrification. The ultimate aim of this thesis was to determine the significance of fungal and bacterial denitrification in arable soil and to investigate influences of soil pH and physical disturbance on potential denitrification rates and denitrifying communities. Long-term pH plots combined with a disturbance gradient have been utilised to investigate fungal and bacterial denitrification distinguished by application of selective inhibitors. Highest N2O production was measured from slightly acidic soil and soil with reduced disturbance. Fungi and bacteria contributed to N2O production with bacterial denitrification as dominant source. Fungal denitrification remained unaffected by soil pH and disturbance whereas bacterial denitrification was influenced by these factors. Bacterial denitrification was positively correlated with concentrations of fatty acids which suggested that these fatty acids were common to bacteria involved in N2O production in the soils investigated here. Bacterial community structure changed with soil pH and disturbance whereas fungal community structure was only influenced by disturbance. Bacterial denitrifier communities (nitrite reductases nirK and nirS) changed over the pH gradient but only the nirK community was affected by disturbance. This indicated that groups of bacterial denitrifiers follow different ecological strategies. Gene abundance of nirK and nirS was also correlated to concentrations of the fatty acids associated with denitrifying bacteria in the soils investigated here. In conclusion, fungal denitrification was significant in arable soil but remained unchanged by soil pH and disturbance. Therefore, fungal denitrification is important in agricultural ecosystems and should be considered when developing mitigation strategies for N2O production especially under conditions favourable for fungal denitrification.

Dissertation submitted in compliance with the requirements for the Master's Degree in Technology: Biotechnology, Technikon Natal, 2001. / Up until now extensive work has been done to develop kinetic models and related software that can be used successfully to simulate and design nitrification denitrification (ND) and nitrification denitrification biological excess phosphorus removal (NDBEPR) systems for efficient nitrogen removal. The denitrification kinetics of these systems have primarily been determined and attributed to the ordinary heterotrophic bacteria, now also known as the OHO fraction, otherwise not involved in biological excess phosphorus removal. However, denitrification kinetics determined for ND systems have been found to vary considerably at times when applied to NDBEPR systems because of varying OHO active fraction estimates and the unexplained occurrence of anoxic phosphorus removal and anysuccess achieved to date has been some what fortuitous. Ultimately variations in process performance and kinetics are attributable to inadequate control and lack of understanding of the ecological, physiological and biochemical activities of constituent microorganisms. There is growing concern and movement towards a better understanding of the microbial community within activated sludge in order to gain optimal control of the process. / M

O principal objetivo desse trabalho foi desenvolver uma nova configuração de biofiltro aerado submerso utilizado no pós-tratamento do efluente de reator UASB, capaz de realizar nitrificação e desnitrificação em um único sistema. Em busca de bases operacionais dessa nova configuração, a pesquisa foi inicialmente conduzida com três reatores seqüenciais. Esses reatores foram dispostos nas seqüências I e II, respectivamente. Os resultados obtidos com esses sistemas seqüenciais levaram a concepção do projeto da nova configuração do biofiltro proposto (BF definitivo). Os resultados da seqüência I mostraram alto potencial para conversão de nitrogênio amoniacal e total, e também alta eficiência na remoção da matéria orgânica carbonácea. Esse sistema, porém, não apresentou potencial para desnitrificação. Na seqüência II foi realizada recirculação entre dois reatores do sistema (anóxico e aeróbio) para aumento de tal potencial. O maior potencial de desnitrificação, nessa seqüência, foi observado para razão de recirculação, Rc, igual a 2,65 e com o uso de 40%, em volume, de esgoto sanitário bruto como fonte de carbono. Sob essas condições operacionais, para concentração média afluente ao sistema igual a 33,74 mg de \'N-\'NH IND.3\'/L as concentrações efluentes médias de \'N-NH IND.3\', \'N-NO IND.2\'POT.-\' e \'N-NO IND.3\'POT.-\' foram, respectivamente, iguais a 0,16, 0,0026 e 9,72 mg/L. Os resultados do BF definitivo mostraram que a nova configuração proposta é viável como unidade de pós-tratamento de efluente de reator UASB, promovendo nitrificação e desnitrificação em um único sistema, além de alta eficiência de remoção da matéria orgânica. Em todas as fases dessa pesquisa, praticamente, todos os resultados obtidos atenderam ao padrão de lançamento de nitrogênio amoniacal estabelecido pela legislação ambiental. / The main objective of this work was developing a new configuration of submerged aerated biofilter used in UASB reactor post-treatment, with nitrification and denitrification in a single system. Searching operational bases of this new configuration, this research was initially driven by three sequential reactors. These reactors were arranged in the sequences I and II, respectively. The results obtained with these sequential systems took the conception of the project of the new configuration of the proposed biofilter (definitive BF). The results of the sequence I showed high ammoniacal and total nitrogen conversion potential, and also high carbonaceous organic matter removal efficiency. This system, however, not presented potential for denitrification. In the sequence II recirculation between two reactors (anoxic and aerated) of the system was made for such potential increasing. The higher denitrification potential, in this sequence, was observed with recirculation reason, Rc, equal to 2,65 and using 40%, in volume, of raw sanitary sewage as carbon source. Under these operational conditions, for average affluent concentration of 33,74 mg of \'N-NH IND.3\'/L the average effluent concentrations of \'N-NH IND.3\', \'N-NO IND.2\'POT.-\' e \'N-NO IND.3\'POT.-\' were, respectively, equal to 0,16, 0,0026 and 9,72 mg/L. The results of the definitive BF showed that the new proposed configuration is feasible as effluent UASB post-treatment unity, with nitrification and denitrification in a single system, besides high organic matter removal efficiency. Practically in all the phases of this research, all the results obtained attended to the launch standard of ammoniacal nitrogen established by the environmental legislation.

A presente dissertação apresenta e discute os resultados do trabalho experimental cujo objetivo foi avaliar a remoção de nitrogênio na forma de mitrato (N-NO3-) pelo processo de desnitrificação biológica em reator anóxico horizontal de leito fixo (RAHLF) contendo matrizes de espuma de poliuretano, em escala de laboratório, utilizando gás metano como fonte de carbono e único doador de elétrons adicionado ao sistema. Para concentrações iniciais de N-NO3- de 20 mg/L e 40 mg/L no substrato sintético, foi possível obter diminuição das concentrações iniciais em 85% e 50%. No entanto, os altos níveis de redução de N-NO3-, obtidos sob condições limitantes de metano, deram suporte à hipótese de que parte da remoção do N-NO3- foi realizada mediante a utilização de compostos reduzidos de enxofre ou nitrogênio, tais como: S0, HS- ou NH4+, provavelmente formados sob condições anóxicas, simultaneamente com o processo de desnitrificação. Foi possível verificar, também, a influência da relação carbono (mg/L CH4 / nitrogênio (mg/L N-NO3-) no estabelecimento das rotas metabólicas de desnitrificação predominantes, quais sejam, a redução dissimilativa do nitrogênio à amônia (RDNA) ou a desnitrificação. Adicionalmente, foram realizados ensaios em reatores tipo batelada, com o objetivo de se medir o consumo de metano. Porém, os resultados não foram satisfatórios, provavelmente em razão da diversidade microbiana presente no inóculo. Foram realizadas análises de microscopia óptica e de fluorescência, assim como de DGGE, para avaliar a diversidade e as alterações nas populações microbianas ao longo do RAHLF e do tempo de experimento. Os diferentes sistemas utilizados apresentaram limitações relacionadas à baixa solubilidade do gás metano no meio líquido, à resistência à transferência de massa da fase gasosa para a líquida e desta última para a biomassa aderida à espuma. / This study presents and discusses experimental work results conducted with the purpose of evaluating nitrate - nitrogen (N-NO3-) removal by biological denitrification process in a lab scale horizontal flow fixed bed anoxic reactor (RAHLF), using methane gas as sole carbon source and electron donor. Support media for microorganisms were polyurethane foam matrixes. For initial N-NO3- concentrations of 20 mg/L and 40 mg/L present in synthetic substrate, it was possible to obtain 85% and 50% removal respectively. These high reduction rates, obtained under limiting conditions of methane, sustained the idea of part of the N-NO3- removal being accomplished by reductive sulfur or nitrogen species utilization, such as: S0, HS- or NH4+, probably formed under anoxic conditions simultaneously to denitrification process. It was possible to verify also carbon (mg/L CH4) / nitrogen (mg/L N-NO3-) ratio effect in denitrification metabolic paths establishment, i.e. dissimilative reduction of nitrogen to ammonia or denitrification itself. In addition, batch tests where conducted with methane consumption measuring purpose. Yet, results where not satisfactory probably due to great microbial diversity present in inoculum. Optical microscopy and fluorescence exams where developed, as well as, DGGE, in order to evaluate diversity and alterations in bacterial populations as a function of reactor\'s length and time. Different systems used in experimental work presented limitations due to low methane gas solubility in bulk liquid and mass transfer resistance from gas to liquid phase and from this to fixed biomass.

The inputs and losses of nitrogen from Great Basin arid soils were studied using the acetylene reduction and 15N techniques. Filamentous blue-green algae were observed to be the predominant algal group in the soil crusts. The bacterial association with this group of algae suggest a phycosphere-like effect, thus allowing heterotrophic nitrogen fixation and denitrification to occur. Up to 17.5 mg N/100 g soil was found to have been fixed in surface soils (0 to 3 em) during a three week incubation period, while 45.9 mg N/100 g soil was fixed in a five week incubation period. Ammonium sulfate and ammonium sulfate plus plant material amendments reduced the gain in nitrogen by 41 to 100 percent. 15 + 15 - Fifty to sixty percent of the applied NH4-N and N0 3-N was denitrified during the first week of incubation while 70 to 80 percent of the NH 4-N was lost in a three- to five-week incubation period. These data suggest that a potential for heterotrophic nitrogen fixation exists, and under optimal conditions, significant gains in soil nitrogen may be achieved. However, in the presence of allelochemic agents, the potential gain in soil nitrogen may be reduced or inhibited. In addition, the denitrification potentials of these soils may also limit the input of nitrogen. The application of protein ( casein) to these soils resulted in an ammonification rate of 50 to 60 percent. 15 Fixed N2 indicated a 21 to 48.8 percent ammonification rate, thus suggesting that the mineraliztion of NH 4 was the rate limiting step for nitrogen loss. Ammonia volatilization accounted for less than a five percent nitrogen loss, regardless of experimental conditions. The inhibitory effects of plant material and litter extracts, and ''N-Serve" on heterotrophic nitrogen fixation has been assessed. The data suggest that the nitrogen fixing population is sensitive to the inhibitory effects of such agents .

Nitrate (NO3) loadings from stormwater runoff promote eutrophication in surface waters. Low Impact Development (LID) is a type of best management practice aimed at restoring the hydrologic function of watersheds and removing contaminants before they are discharged into ground and surface waters. Also known as rain gardens, a bioretention system is a LID technology that is capable of increasing infliltration, reducing runoff rates and removing pollutants. They can be planted with visually appealing vegetation, which plays a role in nutrient uptake. A modified bioretention system incorporates a submerged internal water storage zone (IWSZ) that includes an electron donor to support denitrification. Modified (or denitrifying) bioretention systems have been shown to be capable of converting NO3 in stormwater runoff to nitrogen gas through denitrification; however, design guidelines are lacking for these systems, particularly under Florida-specific hydrologic conditions. The experimental portion of this research investigated the performance of denitrifying bioretention systems with varying IWSZ medium types, IWSZ depths, hydraulic loading rates and antecedent dry conditions (ADCs). Microcosm studies were performed to compare denitrification rates using wood chips, gravel, sand, and mixtures of wood chips with sand or gravel media. The microcosm study revealed that carbon-containing media, acclimated media and lower initial dissolved oxygen concentrations will enhance NO3 removal rates. The gravel-wood medium was observed to have high NO3 removal rates and low final dissolved organic carbon concentrations compared to the other media types. The gravel-wood medium was selected for subsequent storm event and tracer studies, which incorporated three completely submerged columns with varying depths. Even though the columns were operated under equivalent detention times, greater NO3 removal efficiencies were observed in the taller compared to the shorter columns. Tracer studies revealed this phenomenon was attributed to the improved hydraulic performance in the taller compared to shorter columns. In addition, greater NO3 removal efficiencies were observed with an increase in ADCs, where ADCs were positively correlated with dissolved organic carbon concentrations. Data from the experimental portion of this study, additional hydraulic modeling development for the unsaturated layer and unsaturated layer data from other studies were combined to create nitrogen loading model for modified bioretention systems. The processes incorporated into the IWSZ model include denitrification, dispersion, organic media hydrolysis, oxygen inhibition, bio-available organic carbon limitation and Total Kjeldahl Nitrogen (TKN) leaching. For the hydraulic component, a unifying equation was developed to approximate unsaturated and saturated flow rates. The hydraulic modeling results indicate that during ADCs, greater storage capacities are available in taller compared to shorter IWSZs Data from another study was used to develop a pseudo-nitrification model for the unsaturated layer. A hypothetical case study was then conducted with SWMM-5 software to evaluate nitrogen loadings from various modified bioretention system designs that have equal IWSZ volumes. The results indicate that bioretention systems with taller IWSZs remove greater NO3 loadings, which was likely due to the greater hydraulic performance in the taller compared to shorter IWSZ designs. However, the systems with the shorter IWSZs removed greater TKN and total nitrogen loadings due to the larger unsaturated layer volumes in the shorter IWSZ designs.

The influence of effluent addition on denitrification potential in the Thredbo Wetland was observed by comparing an area of the wetland receiving secondary treated effluent with another area receiving no effluent addition. Physico-chemical measurements (Eh, pH and temperature) of the soil were conducted in both sampling areas to characterise the denitrifying environment. Levels of nitrate plus nitrite and ammonium ion in the soil from 0-30cm depth were recorded on a seasonal basis to identify the role of effluent addition and vertical distribution of inorganic nitrogen species in controlling the distribution of denitrification potential in the soil. Denitrification potentials of soils and decaying plant material were evaluated by the acetylene blockage technique. This involved laboratory incubations under optimum conditions of pH, temperature, nitrate concentration, carbon supply, and diffusion. The influence of these physico-chemical factors on denitrification was also investigated. It was found that the effluent addition caused higher denitrification potential in soils and surface decaying plant material by raising soil temperature, lowering Eh, and increasing concentrations of nitrate plus nitrite and ammonium ions. The highest denitrification potential was recorded in the decaying plant material on the soil surface. The highest soil denitrification potential occurred in the 0-6cm depth segment. Carbon supply and pH had no influence on denitrification potential whilst low temperature (5ºC), and restricted diffusion limited denitrification. In terms of tertiary water treatment denitrification in Thredbo Wetland makes a significant-contribution to the removal of nitrogen year-round. However, total nitrogen removal could be increased by increasing the residence time of water in the wetland thereby encouraging greater spatial and temporal interaction between the denitrifiers and the wastewater nitrogen.

<p>Wetlands water quality is influenced by the anthopogenic activities in the catchments’ areas. Wastewaters from the urban storm, agricultural runoff and sewage treatment often end up in wetlands before flowing to rivers, lakes and the sea. A lot of pollutants are readily transported in these wastewaters, thus subjecting the wetland ecosystem into a continuous resilience. Importantly, heavy metals like Cu, Zn, and Pb etc. are constituents of such pollutants in the wastewaters.</p><p>The study has as a specific objective to investigate the effects of heavy metal Cu, Zn and Pb on denitrification, an important ecosystem process and service. In a wetland situation, denitrification is a permanent nitrogen removal process accounting for about 90% of the total nitrogen removal.</p><p>The research was carried out in the laboratory and sediment samples were taken from a constructed wetland in Linkoping. We employed acetylene inhibition technique in obtaining N2O as a product resulting from nitrate reduction. The treatments (Cu, Zn and Pb) levels were 100 mg/kg, 250 mg/kg, 500 mg/kg and 1000 mg/kg of sediment, in three replicates and a control.</p><p>Samplings of the assay were taken within 24hours. Gas chromatography was used to analyse and quantify N2O in the various samples. A linear regression analysis was carried out with Windows Excel and SPSS to compare the various treatments with the control at 95% confidence level.</p><p>The results show that there were no inhibitions of denitrification at 100 mg/kg sediment treatment level for any of the element. Inhibition of denitrification was observed at treatment levels 500 mg/kg and 1000 mg/kg of sediment. The rate of nitrate reduction was compared from the slope of the regression curve. The rate for Cu at 500 mg and 1000 mg /kg of sediment was moderately related to that of the control, Zn shows a similar trend but a higher rate in some samples, while Pb shows more inhibition.</p>

Thesis (Dr. rer. nat.)--Philipps-Universität Marburg, 2002. / Title from PDF t.p. (viewed on Apr. 24, 2007). Includes bibliographical references (p. 143-163).

Thesis (Ph.D.)--York University, 2004. Graduate Programme in Geography. / Typescript. Includes bibliographical references (leaves 182-194). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ99255