The effectiveness of partial ozonation of return activated sludge for enhancing denitrification and waste sludge minimization were examined. A pair of nitrifying sequencing batch reactors was operated in either aerobic or alternating anoxic/aerobic conditions, with one control and one ozonated reactor in each set. The amount of solids decreased with the ozone dose. Biomass in the anoxic/aerobic reactor was easier to destroy than in the aerobic one, generating approximately twice as much soluble chemical oxygen demand (COD) by cell lysis. Increased COD favoured production of extracellular polymers in ozonated reactors, enhancing flocculation and improving settling. Floc stability was also strengthened in prolonged operation in alternating treatment, resulting in declined solids destruction. Dewaterability was better in alternating reactors than in aerobic ones indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation. Ozone successively destroyed indicator estrogenic compounds, contributing to total estrogen removal from wastewater. Denitrification rate improved up to 60% due to additional carbon released by ozonation. Nitrification rates deteriorated much more in the aerobic than in the alternating reactor, possibly as a result of competition created by growth of heterotrophs receiving the additional COD. Overall, ozonation provided the expected benefits and had less negative impacts on processes in the alternating treatment, although after prolonged operation, benefits could become less significant. The alternating anoxic/aerobic reactor achieved twice the nitrification rates of its aerobic counterpart. Higher removal rates of estrogens were associated with higher nitrification rates, supporting the contention that the nitrifying biomass was responsible for their removal. The alternating treatment offered the better estrogen biodegradation. Microbial populations in both reactors were examined with fluorescent in situ hybridization. Dominance of rapid nitrifiers like Nitrosomonas and Nitrobacter (79.5%) in the alternating reactor, compared to a dominance of slower nitrifiers like Nitrosospira and Nitrospira (78.2%) in the aerobic reactor were found. The findings are important to design engineers, as reactors are typically designed based on nitrifiers’ growth rate determined in strictly aerobic conditions. / October 2008

Nitrous oxide (N₂O) is a powerful greenhouse gas, and its atmospheric concentration is increasing dramatically. N₂O is produced through the microbially-mediated processes of nitrification and denitrification. Since these processes have different substrates and isotopic enrichment factors, stable isotope analysis (δ¹⁵N and δ¹⁸O) of N₂O can be used to study the production of this important greenhouse gas. Although production in rivers accounts for a significant portion of the global N₂O budget, the isotopic composition of N₂O from this source is poorly characterized. Most of the previous work using stable isotopes of N₂O has been conducted in terrestrial or oceanic environments, and only one published study has measured δ¹⁵N and δ¹⁸O of N₂O produced in a riverine environment. The purpose of this research project was to use stable isotope analysis to characterize the processes responsible for N₂O production in the Grand River, Ontario, Canada, and to determine the spatial and temporal variability of the isotopic composition of the N₂O flux. To meet the study objectives, an offline “purge and trap” method was developed to collect and purify dissolved N₂O for stable isotope analysis. Using this method, δ¹⁵N and δ¹⁸O analysis of dissolved N₂O is possible for samples with concentrations as low as 6 nmol N₂O/L. Due to the isotopic effects of gas exchange and the back flux of tropospheric N₂O, there is a complex relationship between the δ¹⁵N and the δ¹⁸O of source, dissolved, and emitted N₂O in aquatic environments. A simple box model (SIDNO – Stable Isotopes of Dissolved Nitrous Oxide) was developed to properly interpret isotopic data for dissolved N₂O. Using this model, it was determined that the isotopic composition of emitted N₂O is much more representative of N₂O production in aquatic environments than the isotopic composition of dissolved N₂O. If the concentration, δ¹⁵N and δ¹⁸O of dissolved N₂O are measured, the magnitude and isotopic composition of the N₂O flux can be calculated. Sampling downstream of the major wastewater treatment plants (WWTPs) on the Grand River indicates that nitrification and denitrification in the river are strongly tied to diel changes in dissolved oxygen (DO) concentration. During the day, when DO concentrations are high, nitrification or nitrifier-denitrification is the dominant N₂O production pathway, with sediment denitrification also contributing to N₂O production. At night, when DO concentrations are low, denitrification in the sediments and at the sediment / water interface is the dominant production pathway. Using the SIDNO model, N₂O produced during the day was found to have a δ¹⁵N of -22‰ and a δ¹⁸O of 43‰. N₂O produced at night had a δ¹⁵N of -30‰ and a δ¹⁸O of 30‰. The isotopic composition of N₂O emitted from the Grand River is dominated by night-time production downstream of the Waterloo and Kitchener WWTPs during the summer. The flux and time weighted annual average isotopic composition of N₂O emitted from the Grand River is -18.5‰ and 32.7‰ for δ¹⁵N and δ¹⁸O respectively. These values are significantly more depleted than the only other published data for riverine N₂O production. If the Grand River is representative of global riverine N₂O production, these results will have significant implications for the global isotopic budget for atmospheric N₂O.

This study was made as a part of a feasibility study on a polishing wetland at Rimbo wastewater plant (wwp) in Norrtälje municipality. The wwp had to decrease the nitrogen discharge to reach the limit 15 mg tot-N/l. The nitrogen in the outlet was mainly in the form of nitrate, hence the wetland mainly ought to support denitrification. The proposed area for the wetland was situated right next to the wwp and was already in the municipalitys posession. One aim of this study was to examine what spieces of plants needed to achieve highest possible denitrification. Some different plant spieces for providing a good and interesting environment for birds and people were also proposed. Furthermore a massbalance model was developed for studying the important exchange processes in a wetland, to study the impact of an uneven streambed on the hyporheic water exchange and for trying to predict the wetlands nitrogen removal capacity. Proposed plants to support denitrification was different reeds such as Common reed (Phragmites australis), Bulrush (Typha), Reed Sweet-grass (Glyceria maxima) och Reed Canry-grass (Phalaris Arundinacea). Common reed is a durable species who can survive in deeper water up to 2 metres while the others need a shallower water about 0,5 m of depth. For the good of the birdlife, different spieces of Sedges (Carex) were chosen due to their ability to produce large amounts of nutrient rich seeds. Measurment in sediment cores from Ekeby wetland in Eskilstuna gave a potential denitrification capacity of 3,31 mg NO3-N m-3 sed s-1. The denitrification capacity was then used in a massbalance model were the theory of advective pumping in an uneven bedsurface also was implemented. Evaluation of the model results showed that an uneven bedsurface did not contribute to an increased nitrogen removal from the wetland, possibly due to a far too low advection and flow of the water. This was also a reason to why the distribution between denitrification from the water- and plant community vs the sediment was unbalanced. The model results showed that less than 1 % of the reduced nitrogen came from the sediment part, in contrast to current knowledge that says about 50%. The model and the participating exchange processes need to be further evaluated before the models prediction of nitrogen removal can be used in design of a wetland. Calculations and comparisons with other wetlands showed that with a well estimated, grown up and maintained wetland, there should be no problems in achieving the goal of nitrogen removal in Rimbo wetland. Such a wetland should also provide a good habitat for birds and animals and also be a good recreationarea for people to visit, properties that were appreciated as important effects in other wetlands studied in this work. / Detta arbete gjordes som en del av en förstudie för anläggande av en efterpolerande våtmark till reningsverket i Rimbo, Norrtälje kommun. Reningsverket behövde sänka sitt utsläpp av kväve till riktvärdet 15 mg tot-N/l. Huvuddelen av kvävet i utloppsvattnet förelåg i nitratform, varför denitrifikationen borde förstärkas genom att anlägga en våtmark. Det tilltänkta området för våtmarken ligger i anslutning till reningsverket och ägs idag av kommunen. I detta arbete undersöktes vilken växtlighet i våtmarken som var lämpligast för syftet att få en så bra denitrifikation som möjligt. Även olika växtarter för att ge en intressant miljö för fåglar och människor togs fram. Dessutom utvecklades en massbalansmodell som användes för att studera de utbytesprocesser som är viktiga i en våtmark, frågan hur en ojämn bottenmorfometri påverkar det hyporheiska vattenutbytet samt om det går att förutsäga reningskapaciteten i Rimbo våtmark. Lämpliga växter för denitrifikationen ansågs vara vassbildande växter, och då främst främst bladvass (Phragmites australis), men även kaveldun (Typha), jättegröe (Glyceria maxima) och rörflen (Phalaris Arundinacea). Bladvass är en mycket tålig växt som klarar stort vattendjup, medan de andra vassorterna behöver en grundare våtmark på ca 0,5 m. För fågellivets bästa ansågs starrväxter (Carex) vara viktiga arter då de producerar stora mängder frön. Mätning av denitrifikationspotentialen i sediment från Ekeby våtmark gav en hastighet för denitrifikationen i sedimentet på 3,31 mg NO3-N m-3 sed s-1. Denitrifikationen från sediment användes sedan i en massbalansmodell där även även teorin om advektivt pumputbyte vid ojämn bottenform implementerades. En utvärdering av modellresultaten kunde avgöra att en ojämn eller vågig bottenmorfometri inte skulle förbättra reningen i våtmarken. Detta beroende på bland annat för låg advektionshastighet och flöde. Detta låga flöde ned i sedimentet bidrog även till att fördelningen av kväveborttag från sediment respektive vatten- och växtdelen blev snedfördelad. Enligt modellen var det mindre än 1% av kvävet som togs bort från sedimentet medan all vetenskap tyder på närmare 50%. Modellen och de ingående utbytesprocesserna bör utvärderas och utvecklas ytterligare innan den kan användas som verktyg för att beräkna kvävereningen från en våtmark. Beräkningar och jämförelser med andra våtmarker visade dock att en väl beväxt, utförd och beskickad våtmark inte skulle ha några problem att sänka nitrathalten till riktvärdet. En våtmark skulle även utgöra en bra uppehållsmiljö för fåglar, djur och människor vilket anses som viktiga mervärden i våtmarker på andra platser i Sverige.

Nitrous oxide (N₂O) is a powerful greenhouse gas, and its atmospheric concentration is increasing dramatically. N₂O is produced through the microbially-mediated processes of nitrification and denitrification. Since these processes have different substrates and isotopic enrichment factors, stable isotope analysis (δ¹⁵N and δ¹⁸O) of N₂O can be used to study the production of this important greenhouse gas. Although production in rivers accounts for a significant portion of the global N₂O budget, the isotopic composition of N₂O from this source is poorly characterized. Most of the previous work using stable isotopes of N₂O has been conducted in terrestrial or oceanic environments, and only one published study has measured δ¹⁵N and δ¹⁸O of N₂O produced in a riverine environment. The purpose of this research project was to use stable isotope analysis to characterize the processes responsible for N₂O production in the Grand River, Ontario, Canada, and to determine the spatial and temporal variability of the isotopic composition of the N₂O flux. To meet the study objectives, an offline “purge and trap” method was developed to collect and purify dissolved N₂O for stable isotope analysis. Using this method, δ¹⁵N and δ¹⁸O analysis of dissolved N₂O is possible for samples with concentrations as low as 6 nmol N₂O/L. Due to the isotopic effects of gas exchange and the back flux of tropospheric N₂O, there is a complex relationship between the δ¹⁵N and the δ¹⁸O of source, dissolved, and emitted N₂O in aquatic environments. A simple box model (SIDNO – Stable Isotopes of Dissolved Nitrous Oxide) was developed to properly interpret isotopic data for dissolved N₂O. Using this model, it was determined that the isotopic composition of emitted N₂O is much more representative of N₂O production in aquatic environments than the isotopic composition of dissolved N₂O. If the concentration, δ¹⁵N and δ¹⁸O of dissolved N₂O are measured, the magnitude and isotopic composition of the N₂O flux can be calculated. Sampling downstream of the major wastewater treatment plants (WWTPs) on the Grand River indicates that nitrification and denitrification in the river are strongly tied to diel changes in dissolved oxygen (DO) concentration. During the day, when DO concentrations are high, nitrification or nitrifier-denitrification is the dominant N₂O production pathway, with sediment denitrification also contributing to N₂O production. At night, when DO concentrations are low, denitrification in the sediments and at the sediment / water interface is the dominant production pathway. Using the SIDNO model, N₂O produced during the day was found to have a δ¹⁵N of -22‰ and a δ¹⁸O of 43‰. N₂O produced at night had a δ¹⁵N of -30‰ and a δ¹⁸O of 30‰. The isotopic composition of N₂O emitted from the Grand River is dominated by night-time production downstream of the Waterloo and Kitchener WWTPs during the summer. The flux and time weighted annual average isotopic composition of N₂O emitted from the Grand River is -18.5‰ and 32.7‰ for δ¹⁵N and δ¹⁸O respectively. These values are significantly more depleted than the only other published data for riverine N₂O production. If the Grand River is representative of global riverine N₂O production, these results will have significant implications for the global isotopic budget for atmospheric N₂O.

Hydrogen sulphide (H2S) is a serious problem for many industries, including oil production and processing, pulp and paper, and wastewater treatment. In addition, H2S is usually present in natural gas and biogas. It is necessary to control the generation and release of H2S into the environment because H2S is corrosive, toxic, and has an unpleasant odour. In addition, the removal of H2S from natural gas and biogas is essential for preventing the emission of SO2 upon combustion of these gases. Physicochemical processes have been developed for the removal of H2S. These processes employ techniques such as chemical or physical absorption, thermal and catalytic conversion, and liquid phase oxidation. In comparison, biological processes for the removal of sulphide typically operate at ambient temperature and pressure, with the feasibility for the treatment of smaller streams, and the absence of expensive catalysts. The objective of the present work was to study the biooxidation of sulphide under denitrifying conditions in batch system and a continuous immobilized cell bioreactor using a mixed microbial culture enriched from the produced water of a Canadian oil reservoir. <p>In the batch experiments conducted at various initial sulphide concentrations, an increase in the sulphide oxidation and nitrate reduction rates was observed as the initial sulphide concentration was increased in the range 1.7 to 5.5 mM. An extended lag phase of approximately 10 days was observed when sulphide concentrations around or higher than 14 mM were used. This, when considered with the fact that the microbial culture was not able to oxidize sulphide at an initial concentration of 20 mM, indicates the inhibitory effects of sulphide at high concentrations.<p>The effect of the initial sulphide to nitrate concentrations ratio (ranging from 0.3 to 4.0) was also studied. As the initial sulphide to nitrate ratio decreased, the sulphide oxidation rates increased. The increasing trend was observed for initial nitrate concentrations in the range of 1.3 to 7.3 mM, corresponding to ratios of 4.08 to 0.83. The increase in nitrate reduction rates was more pronounced than that of the sulphide oxidation rates. However at nitrate concentrations higher than 7.3 mM (ratios lower than 0.83) the nitrate reduction rate remained constant. The percentage of sulphide that was oxidized to sulphate increased from 2.4% to 100% as the initial sulphide to nitrate ratio decreased from 4.08 to 0.42. This indicated that at ratios lower than 0.42, nitrate would be in excess and at ratios exceeding 4.08, nitrate would be limiting. In the continuous bioreactor systems, at sulphide loading rates ranging from 0.26 to 30.30 mM/h, sulphide conversion remained in the range of 97.6% to 99.7%. A linear increase in the volumetric oxidation rate of sulphide was observed as the sulphide loading rate was increased with the maximum rate being 30.30 mM/h (98.5% conversion). Application of immobilized cells led to a significant increase in oxidation rate of sulphide when compared with the rates obtained in a bioreactor with freely suspended cells. At nitrate loading rates ranging from 0.19 to 24.44 mM/h, the nitrate conversion ranged from 97.2% to 100% and a linear increase in volumetric reduction rate was observed as the nitrate loading rate was increased, with the maximum rate being 24.44 mM/h (99.7% conversion). <p>A second bioreactor experiment was conducted to investigate the effects of sulphide to nitrate concentrations ratio on the performance of the system. Sulphide conversion was complete at sulphide to nitrate ratios of 1.1 and 1.3, but decreased to 90.5% at the ratio of 3.1 and 65.0% at the ratio of 5.0, indicating nitrate was limiting for sulphide to nitrate ratios of 3.1 and 5.0. The increase in the sulphide to nitrate ratio (and the resulting limitation of nitrate) caused a decrease in the volumetric reaction rate of sulphide.<p>Nitrate conversion was complete at sulphide to nitrate ratios of 1.3, 3.1, and 5.0; however, at a ratio of 1.1, the conversion of nitrate dropped to 59.6%, indicating that nitrate was in excess, and sulphide was limiting. The volumetric reaction rate of nitrate decreased as the sulphide to nitrate ratio increased for ratios of 1.3, 3.1, and 5.0; this was due to the decrease in the nitrate loading rate. For sulphide to nitrate ratios of 1.1 and 1.3, 7.2% and 19.6% of the sulphide was converted to sulphate, respectively. At ratios of 3.1 and 5.0, no sulphate was generated. For ratios between 1.3 and 5.0, an increase in the ratio caused a decrease in the generation of sulphate.

Human actions have led to the destruction or degradation of natural habitats in virtually all parts of the Earth. Ecosystem restoration is one method to mitigate the effects of habitat loss. But restoration ecology is a young discipline and there is much left to be learned about how to effectively restore ecosystem functioning. This dissertation examines how soil amendments and planted herbaceous species diversity affect the restoration of ecosystem functions in wetlands, while also testing basic ecological questions that help us understand ecosystem function. Using data from the greenhouse and from the biodiversity and ecosystem function field experiment in Duke Forest, in Durham, NC, I examine how plant trait diversity, average plant traits, and environmental conditions influence nitrogen (N) removal from restored wetlands. Field data collected from a restored wetland in Charlotte, NC, enables me to examine how soil organic amendments influence the development of soil properties, processes, and plant communities. Finally, combining field data from both sites, I compare how soil properties influence denitrification potential in both restored wetlands. One unanswered question in the research relating biodiversity and ecosystem function is whether species diversity or species traits are more important drivers of ecosystem function. The first portion of my dissertation poses several hypotheses about how plant traits, plant trait diversity (calculated as a multivariate measure of plant trait diversity), and environmental conditions are likely to influence two ecosystem functions, biomass N and denitrification potential (DEA), and then examines these hypotheses in a restored wetland in the Piedmont of N.C. Using multiple linear regression, I demonstrate that functional diversity (FD), of traits important for plant growth had no effect on biomass N, but two plant traits, leaf area distribution ratio (LADR) and water use efficiency (WUE), had strong negative effects. Soil inorganic N also had a positive effect. For DEA, FD of traits related to denitrification also did not have a significant effect, but there was evidence of a weak positive effect. Two plant traits had positive effects on DEA, aboveground biomass and aboveground biomass C:N ratio; two traits, belowground biomass C:N ratio and root porosity, had negative effects. Soil inorganic N and soil organic matter also had positive effects on DEA. Results from a Principal Components Analysis (PCA) clustering plant species in trait-space, suggest that <em>Carex</em>, <em>Scirpus</em>, and <em>Juncus</em> species tend to be associated with traits that maximize biomass N, while there is no specific region of trait space or set of species that correspond to high DEA. Instead, there are multiple plant trait combinations that can lead to high DEA. These results suggest that, even though plant diversity (as measured by FD) does not significantly influence biomass N or denitrification, plant trait diversity is important to maintaining multiple ecosystem functions simultaneously. Restored wetlands tend to have lower levels of soil organic matter than natural reference wetlands. Low soil organic matter can limit nutrient cycling as well as plant survival and growth in restored wetlands. In the second portion of my dissertation, I examine how soil compost amendments influence the development of soil properties and processes as well as plant communities at a restored wetland in Charlotte, NC. Using two-way analyses of variance, multiple comparisons of means, and regression, I determine that available N and phosphorus (P) increase with increasing soil organic matter in both the low and high marsh. Total microbial biomass (MB) and microbial activity (measured by denitrification potential (DEA)) also significantly increase with increasing organic matter in both marsh communities, as does soil moisture. Neither total plant biomass (in the low marsh), nor plant species richness (in the high or low marsh) demonstrate any consistent patterns with soil organic matter level in the first three years post-restoration. These results suggest that compost amendments can positively influence some soil properties (i.e. soil available N, P, microbial biomass, and soil moisture) and some ecosystem functions including nutrient cycling (such as denitrification potential), but may have limited early impacts on plant communities. In restoration ecology there is a general assumption that restoring ecosystem structure will also restore ecosystem function. To test this fundamental assumption, I examine whether two restored wetlands demonstrate similar general relationships between soils variables (i.e. do the two systems have similar soil ecosystem structure), and whether the importance of each soil relationship is the same at both systems (i.e. do the two systems demonstrate the same soil function). I use structural equation modeling to both pose hypotheses about how systems function and to test them using field data. I determine that the same model structure of soil relationships is supported by data from these two distinct, yet typical urban restored wetland ecosystems (that is, the two systems have similar soil structure). At both systems higher soil organic matter is the most important predictor of higher DEA; however, most of the other relationships between soils variables are different at each system (that is, the two systems are not functioning in the same way). These results suggest that some fundamental relationships between soil properties and microbial functioning persist even when restored wetlands have very different land-use histories, plant communities, and soil conditions. However, restoring similar soil ecosystem structure does not necessarily lead to the restoration of similar soil function. Ultimately, I hope this research advances our understanding of how ecosystems function and improves future wetland restoration efforts. / Dissertation

<p>Whether through sea level rise, farmland abandonment, or wetland restoration, agricultural soils in coastal areas will be inundated at increasing rates, renewing connections to sensitive surface waters and raising critical questions related to environmental tradeoffs. Wetland restoration in particular is often implemented not only to promote wildlife habitat, but also to improve water quality through nutrient removal, especially in agricultural catchments. The microbial process of denitrification is the central mechanism of nitrogen removal in wetlands and flooded soils, and can be seen as a potential environmental benefit of flooding agricultural lands. While denitrification undoubtedly can remove nitrogen from soil and surface water, higher soil moisture or flooding in wetland soils can also increase the production of greenhouse gases, specifically nitrous oxide and methane, representing a potential environmental tradeoff. Understanding the likely benefits of denitrification and the likely greenhouse gas costs of wetland restoration could help inform environmental policies concerning wetland restoration. </p> <p>Determining whether restored wetlands are larger sources of greenhouse gases compared to contrasting land use types (agriculture and forested wetlands) was the first goal of this dissertation (Chapter 2). We measured gas fluxes from soil and water to the atmosphere, and related environmental variables, in four sites over two years to estimate fluxes of the three major greenhouse gases. We found that carbon dioxide was the major contributor to the radiative balance across all sites, but that in the agricultural site and one of the forested wetland reference sites, nitrous oxide was the second most important contributor. Many studies have shown that methane is more important that nitrous oxide in most freshwater wetlands, as we found in the other forested wetland reference site and in flooded parts of the restored wetland. Overall, we did not find higher greenhouse gas fluxes in the restored wetland compared to agricultural soils or forested wetlands.</p> <p>The controls over nitrous oxide are especially complex, because it can be produced by two complementary processes, nitrification and denitrification, which generally occur under different conditions in the environment. In Chapter 3, we determined the soil and environmental factors that best predicted nitrous oxide fluxes for a subset of our data encompassing gas fluxes measured in November 2007. We found that soil temperature and soil carbon dioxide flux, along with ammonium availability and denitrification potential, were good predictors of nitrous oxide (adj R<super>2</super>=0.81). Although the nitrous oxide model did not perform as well when applied to data from another sampling period, we expect to further develop our modeling efforts to include possible non-linear temperature effects and a larger range of environmental conditions. </p> <p>In Chapter 4, we present results of a stable isotope tracer experiment to determine the relative contribution of nitrification and denitrification to nitrous oxide fluxes in these different land use types, and to determine the response of these processes to changing soil moisture. We added two forms of nitrogen-15 to intact soil cores to distinguish nitrification from denitrification, and subjected the cores to drainage or to a simulated rain event. We found that across the range of soil moisture, the fraction of nitrous oxide produced by denitrification did not change, but within each soil type there was a response to the simulated rain. In mineral soils, the nitrous oxide fraction increased with increasing soil moisture, with the highest mole fraction [N₂O/(N₂+N₂O)] in the agricultural soils, while in the organic soils there was no change or even a decrease. The fraction of nitrous oxide derived from coupled nitrification-denitrification increased with increasing soil moisture, and was much higher than that from denitrification alone in the more organic soils. This suggests that, in these saturated acid-organic soils, nitrification plays an important and underappreciated role in contributing to nitrous oxide fluxes from freshwater wetlands. The results from the laboratory experiment were consistent with patterns we saw in the field and help explain the differential contribution of nitrification and denitrification to nitrous oxide fluxes in different land use types in coastal plain wetlands of North Carolina. </p> <p>Overall, we found that both nitrification and denitrification contribute to nitrous oxide fluxes in coastal plain wetlands in North Carolina, and that nitrification is an especially important source in acid-organic soils under both field-moist and saturated conditions. Although freshwater wetlands, with an average nitrous oxide mole fraction of 0.08, are generally seen as being insignificant sources of nitrous oxide, our study sites ranged from 0.10 to 0.30, placing them closer to agricultural fields (0.38; Schlesinger 2009). Although the ecosystems in our study produced more nitrous oxide than expected for freshwater wetlands, we found no significant tradeoff between the local water quality benefits conferred by denitrification and the global greenhouse gas costs in the restored wetland. These results suggest that, from a nitrogen perspective, wetland restoration in coastal agricultural lands has a net environmental benefit.</p> / Dissertation

Fixed nitrogen is important as a nutrient for organic matter formation and as an electron donor (nitrification) and acceptor (denitrification) for energy generation, but it is scarcely available in aquatic systems. Nitrification oxidizes ammonium to nitrite and nitrate. Denitrification uses these fixed species to form dinitrogen gas. The classic understanding of the nitrogen cycle requires dissolved oxygen for nitrification and assumes denitrification reduces nitrate to dinitrogen through various intermediates in anaerobic conditions. The global nitrogen budget is imbalanced with more marine denitrification measrued than previously estimated in the classic nitrogen cycle, suggesting alternative anaerobic nitrification and denitrification pathways exist. One alternative denitrification pathway is anammox, which directly oxidizes ammonium to dinitrogen with nitrite as the electron acceptor. Other alternative pathways for both nitrification and denitrification involve redox metals as catalysts. Manganese-catalyzed anaerobic nitrification and denitrification are thermodynamically favorable at neutral pH. However, experimental evidence for these processes is still lacking. This investigation seeks to uncover evidence of manganese-catalyzed nitrification and denitrification in saltmarsh sediments. Batch reactors with anaerobic sediment slurries from a saltmarsh in coastal Georgia were incubated in the presence and absence of colloidal manganese oxides and isotope-labeled ammonium and nitrate to trace dinitrogen formation. Results show that denitrification is more prominent in the manganese-treated reactors and that the classic denitrification pathway may not be substantial in shallow saltmarsh sediments. These data indicate that anammox and/or manganese-coupled denitrification are major contributors to the removal of fixed nitrogen. Ammonium removal in the manganese-treated reactors is accompanied by a high nitrite production compared to the nitrogen-only treatment, indicating manganese-coupled denitrification exists and/or anammox is promoted in the presence of manganese. Primary productivity is generally high in saltmarshes, but oxygen penetrates less than a few millimeters in the sediment. These observations suggest that oxygenic nitrification does not fuel denitrification below the sediment-water interface. The data show that manganese may play a role in the formation of nitrite and nitrate in oxygen-limited sediments.

The main contents of campus sewage are BOD and inorganic nutrients. Conventional secondary treatment processes can remove BOD efficiently, whereas the inorganic nutrients remain mostly left. Therefore, the effluents may cause eutrophication to the receiving water bodies. Using constructed wetland treatment system to reduce nutrients become more and more popular recently. Vertical flow type subsurface process is particularly efficient in nitrogen transformations. In this research we studied the nitrogen transformation dynamics by using different types vertical flow constructed wetland system with various natural materials as the media to treat the secondary effluents from a campus sewage treatment plant. Six self designed experiment columns with broken concrete blocks, oyster shells, different sizes of marble granules, and river sands were used for this study as vertical flow constructed wetland systems. The methods of operation included batch type, continuous flow with filled water and trickling filter type, which were tested by controlling the influent flows into those six test columns. The efficiencies of various combinations in treatments and their mechanisms were discussed in the study. The experimental results showed that the best ammonium nitrogen removal efficiency was measured equal to 46.6% in batch type operations, while the continuous flow with filled water type operation showed the best performance by using concrete blocks as the media (42.8%). However, the best ammonium nitrogen removal rate in the trickling operation was found in the column with media of 3 mm marble granules (91.1%). The medium of river sand obtained the best phosphorous removal rate by using a batch flow operation. Vegetating presented only minor contributions in the column with medium of smaller grain size materials. The optimum C/N ratios for denitification tests are 3.5 and 3 by using the media of concrete and oyster, respectively.

The aim of this investigation was to use hybrid constructed wetlands to treat the secondary effluents from NSYSU campus sewage treatment plant, which had high phosphate and ammonium nitogen and from a textile industrial wastewater treatment plant, which had high chemical oxygen demand(COD) . The purpose of this study is to design optimum operation, conditions and to select suitable types of filter media through optimum combinations of vertical flow (VF) and horizontal flow (HF) constructed wetland systems. The flow regimes for vertical flow operation in this study include continuous flow with filled water, trickling filter type and batch type, while the flow types for horizontal flow operation include high water level and low water level effluents. The experimental of results showed that the best ammonium nitrogen removal efficiency was found in trickling filter type, which was because high oxygen was provided under this flow pattern creating a suitable condition for nitrification , especially in V3 column(39.09%), while the best denitrification effect was fonnd in low water level horizontal operation, especially in H2 bed(42.56%). The experimental results of treating the Everest effluent from the wastewater treatment plant showed that the flow regime in V3 system had best removal of COD in batch type. In trickling filter and low water level type, the optimum hybrid of V3+H3 had the COD removal efficiency eqail to(33.3%)+(49.8%) respectirely .For the experimental results of tolerance of macrophyte, Hedycbium coronarium Koenig live well, but no significant removal efficiencies of nutrient was fund.