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Nitrous oxide (N2O) is a potent greenhouse gas and ozone-depleting compound known to be emitted from wastewater treatment. Emissions of N2O results from the activity of the microorganisms employed in the transformation of reactive nitrogen species (NOx). N2O emissions from wastewater treatment are currently underestimated by United Nations (UN) and the United States (US) Environmental Protection Agency (EPA) guidelines, and treatment plants show differing rates of N2O emissions. Improving our understanding of the mechanisms that drive N2O production and subsequent emissions are essential for its mitigation. N2O is produced by a variety of microbial metabolic pathways; this thesis primarily focuses on N2O production via the denitrification pathway. Denitrification, conducted by heterotrophic bacteria is the Dissimilatory reduction of nitrogen oxides such as nitrate (NO3-) or nitrite (NO2-) to di-nitrogen gas (N2), using carbon as electron donors. The process occurs in a cascade reducing NO3-, to NO2-, nitric oxide (NO), N2O and finally N2. This process is catalyzed by several enzymes including, nitrate reductase (Nar, and Nap), nitrite reductase (Nir) nitric oxide reductase (Nor) and nitrous oxide reductase (NosZ). Denitrification is a widespread trait, and the pathway is encoded by a variety of genes, which produce functionally equivalent enzymes but form differing denitrifying phylogenies. For example, nitrite reductase is encoded by nirS and nirK the genes for the cytochrome-cd1 and copper-based dissimilatory nitrite reductases, respectively, while nitrous oxide reductase is encoded by either the truncated or non-truncated gene nosZII or nosZI respectively. It has been proposed that differences in the microbial population may explain the difference in N2O emission observed between treatment plants. This hypothesis is supported by the recent discovery of non-denitrifying N2O reducing organisms encoded by the gene nosZII. These organisms lack the preceding enzymes of the denitrifying pathway but retain the ability to reduce N2O, they have a high abundance in soils, and nosZII abundance shows a strong correlation with reduced N2O emissions. The understanding of denitrifying microbial ecology and its role in the production of N2O from wastewater treatment is currently limited. The primary aim of this thesis is to address the hypothesis: Denitrifying ecology determines the magnitude and rate of N2O accumulation in Wastewater treatment plant (WWTP) sludge. To address this hypothesis, a stepwise approach has been taken. 1) A survey of the microbial ecology of three New Zealand (NZ) WWTPs was conducted to determine denitrifying ecology by the distribution of denitrifying functional markers (nirS, nirK, nosZI, and nosZII) within each population. The following hypotheses were tested, a) denitrifying populations will differ between WWTPs, and b) Wastewater is a disadvantageous environment for non-denitrifying organisms (nosZII), and they will be under-represented. 2) Using the sludges from the surveyed WWTPs, sludge metabolism was examined under ideal denitrifying conditions for differences in NOx profiles including N2O accumulation. Accumulation of NOx intermediaries was correlated with the relative abundance of denitrifying functional markers, testing the hypotheses c) differing denitrifying populations accumulate different amounts of N2O, and d) N2O accumulation will correlate with non-denitrifying organism abundance. 3) As wastewater treatment plants are not stable environments and can suffer from process perturbations, sludges with now known populations, and NOx profiles under control conditions, were exposed to environmental shocks (pH and nitrite (NO2-). Testing the hypothesis: e) Within a specific range of environmental shock, denitrifying population structure will determine N2O accumulation. Survey of NZ microbial populations supports the hypotheses, showing differing total microbial and denitrifying populations, with low abundance of non-denitrifying N2O reducing organisms(nosZII). Analysis of the relative abundance of denitrifying functional markers suggests NZ WWTPs have a genetic predisposition to N2O emissions. Additional findings include the identification of co-occurring nirK and nirS in the same organisms in each treatment plant and the observation that NZ treatment plants show the opposite trend to most of the literature reports with a markedly dominant nirK over nirS population. Examination of the NOx profiles of the three sludges under ideal denitrifying conditions supports the hypotheses showing differing N2O accumulation in each sludge and increasing abundance of nosZII correlating with a decrease in the maximum N2O concentration. All sludges acclimatized to laboratory conditions quickly accumulating minimal N2O after just four sequence batch cycles. Analysis of changes in the rate of NO3- reduction and the Max N2O accumulation suggests that under stable conditions N2O accumulation will be minimal. Examination of the population's response to environmental shock supports the hypothesis, with different populations accumulating N2O when exposed to different environmental shocks. No population was susceptible to N2O accumulation under all conditions. Populations that exhibited NO2- accumulation were resistant to NO2- shock but more susceptible to changes in pH, while populations exhibiting minimal NO2- accumulation were sensitive to NO2- shock but more resistant to changes in PH accumulation. This research concludes that denitrifying microbial populations determine the accumulation of N2O in response to changes in environmental conditions. Denitrifying populations differ between WWTPs. However, results suggest, irrespective of the denitrifying microbial population's structure, stable conditions will result in minimal N2O accumulation. When exposed to environmental shock differing populations showed susceptibility to accumulated N2O under differing environmental conditions. These results suggest that management of N2O accumulation and subsequent emissions will need to be on a case by case basis. Emissions may be addressed by the introduction of a microbial population less susceptible to the N2O accumulation under the environmental conditions of a given treatment plant. Further research is required to test the feasibility of this management strategy.
Anthropogenic activity has clearly altered the N cycle contributing (among other factors) to climate change. This book aims to provide new biotechnological approach representing innovative strategies to solve specific problems related to the imbalance originating in the N cycle. Aspects such as new conceptions in agriculture, wastewater treatment, and greenhouse gas emissions are discussed in this book with a multidisciplinary vision. A team of international authors with wide experience have contributed up-to-date reviews, highlighting scientific principles and their environmental importance and integrating different biotechnological processes in environmental technology.
Nitrogen in the Marine Environment provides information pertinent to the many aspects of the nitrogen cycle. This book presents the advances in ocean productivity research, with emphasis on the role of microbes in nitrogen transformations with excursions to higher trophic levels. Organized into 24 chapters, this book begins with an overview of the abundance and distribution of the various forms of nitrogen in a number of estuaries. This text then provides a comparison of the nitrogen cycling of various ecosystems within the marine environment. Other chapters consider chemical distributions and methodology as an aid to those entering the field. This book discusses as well the enzymology of the initial steps of inorganic nitrogen assimilation. The final chapter deals with the philosophy and application of modeling as an investigative method in basic research on nitrogen dynamics in coastal and open-ocean marine environments. This book is a valuable resource for plant biochemists, microbiologists, aquatic ecologists, and bacteriologists.
This book systematically investigates the nitrogen removal characteristics of two screened aerobic denitrifying bacteria and their applications in nitrogen oxides emissions reduction. It reveals that Pseudomonas stutzeri PCN-1 possesses excellent capacity for aerobic nitrogen removal, regardless of whether nitrate, nitrite or N2O were taken as denitrification substrates. It also demonstrates that the rapid N2O reduction is due to the coordinate expression of denitrification genes. Further, the book discusses the bioaugmentation experiments conducted in denitrifying SBR and a pilot-scale Carrousel oxidation ditch, which confirmed that the strain could significantly enhance denitrification performance, reduce N2O emission and improve system stability. The second strain, P.aeruginosa PCN-2 accumulated negligible NO during aerobic nitrate and nitrite removal and efficiently removed NO from flue gas. This study is of great significance for potential applications of aerobic denitrification in mitigating nitrogen oxides emissions from biological nitrogen removal systems.
Nitrification and denitrification are essential processes for aquatic ecological system and vital for human health. While ammonia is applied for disinfection together with chlorine to produce chloramine, excessive ammonia may cause nitrification and bacteria growth in water transmission pipeline. Since excessive discharge may cause eutrophication and deterioration of aquatic system, nitrate is regulated for wastewater discharge in sensitive areas. Further, nitrate needs to be monitored and controlled in drinking water treatment to protect against methemoglobinemia in bottle-fed infants.
Aerobic Granular Sludge has recently received growing attention by researchers and technology developers, worldwide. Laboratory studies and preliminary field tests led to the conclusion that granular activated sludge can be readily established and profitably used in activated sludge plants, provided 'correct' process conditions are chosen. But what makes process conditions 'correct'? And what makes granules different from activated sludge flocs? Answers to these question are offered in Aerobic Granular Sludge. Major topics covered in this book include: Reasons and mechanism of aerobic granule formation Structure of the microbial population of aerobic granules Role, composition and physical properties of EPS Diffuse limitation and microbial activity within granules Physio-chemical characteristics Operation and application of granule reactors Scale-up aspects of granular sludge reactors, and case studies Aerobic Granular Sludge provides up-to-date information about a rapidly emerging new technology of biological treatment.
Progress in Environmental Engineering contains theoretical and experimental contributions on water purification, new concepts andmethods of wastewater treatment, and ecological problems in freshwater ecosystems. The issues dealt with in the book include: (i) Causes and control of activated sludge bulking and foaming (ii) e use of new support materials in activated sludge technology as a result of studies on wastewater treatment in a sequencing batch reactor with keramsite grains as the porous carrier in Moving Bed Sequencing Batch Biofi lm Reactors (iii) Greenhouse gas emissions from WWTPs especially mechanisms of N2O production in biological wastewater treatment under nitrifying and denitrifying conditions and strategies to mitigate N2O emissions from biological nitrogen removal systems as well as spatiotemporal variation of nitrous oxide emissions from reservoirs ( iv) Novel techniques of water protection against eutrophication and reclamation, in particular aspects of chemical methods of reclamation e.g. using lime for the inactivation of phosphate (v) A method for risk management in water distribution system operation and maintenance using Bayesian process. e proposed method makes it possible to estimate the risks associated with the possibility of partial or total loss of the ability of water supply system operation. Progress in Environmental Engineering includes unique contributions to understand selected aspects of environmental protection and proposes methods to eff ectively solve pollution problems. The book will be of interest to academia and professionals interested or involved in environmental engineering.
Nitrogen in the Environment: Sources, Problems, and Management is the first volume to provide a holistic perspective and comprehensive treatment of nitrogen from field, to ecosystem, to treatment of urban and rural drinking water supplies, while also including a historical overview, human health impacts and policy considerations. It provides a worldwide perspective on nitrogen and agriculture. Nitrogen is one of the most critical elements required in agricultural systems for the production of crops for feed, food and fiber. The ever-increasing world population requires increasing use of nitrogen in agriculture to supply human needs for dietary protein. Worldwide demand for nitrogen will increase as a direct response to increasing population. Strategies and perspectives are considered to improve nitrogen-use efficiency. Issues of nitrogen in crop and human nutrition, and transport and transformations along the continuum from farm field to ground water, watersheds, streams, rivers, and coastal marine environments are discussed. Described are aerial transport of nitrogen from livestock and agricultural systems and the potential for deposition and impacts. The current status of nitrogen in the environment in selected terrestrial and coastal environments and crop and forest ecosystems and development of emerging technologies to minimize nitrogen impacts on the environment are addressed. The nitrogen cycle provides a framework for assessing broad scale or even global strategies to improve nitrogen use efficiency. Growing human populations are the driving force that requires increased nitrogen inputs. These increasing inputs into the food-production system directly result in increased livestock and human-excretory nitrogen contribution into the environment. The scope of this book is diverse, covering a range of topics and issues from furthering our understanding of nitrogen in the environment to policy considerations at both farm and national scales.
For information on the online course in Biological Wastewater Treatment from UNESCO-IHE, visit: http://www.iwapublishing.co.uk/books/biological-wastewater-treatment-online-course-principles-modeling-and-design Over the past twenty years, the knowledge and understanding of wastewater treatment have advanced extensively and moved away from empirically-based approaches to a first principles approach embracing chemistry, microbiology, physical and bioprocess engineering, and mathematics. Many of these advances have matured to the degree that they have been codified into mathematical models for simulation with computers. For a new generation of young scientists and engineers entering the wastewater treatment profession, the quantity, complexity and diversity of these new developments can be overwhelming, particularly in developing countries where access is not readily available to advanced level tertiary education courses in wastewater treatment. Biological Wastewater Treatment addresses this deficiency. It assembles and integrates the postgraduate course material of a dozen or so professors from research groups around the world that have made significant contributions to the advances in wastewater treatment. The book forms part of an internet-based curriculum in biological wastewater treatment which also includes: Summarized lecture handouts of the topics covered in book Filmed lectures by the author professors Tutorial exercises for students self-learning Upon completion of this curriculum the modern approach of modelling and simulation to wastewater treatment plant design and operation, be it activated sludge, biological nitrogen and phosphorus removal, secondary settling tanks or biofilm systems, can be embraced with deeper insight, advanced knowledge and greater confidence.