Advanced wastewater treatment plants must meet permit requirements for organics, solids, nutrients and indicator bacteria, while striving to do so in a cost effective manner. This requires meeting day-to-day fluctuations in climate, influent flows and pollutant loads as well as equipment availability with appropriate and effective process control measures. A study was carried out to assess performance and process control strategies at the Falkenburg Road Advanced Wastewater Treatment Plant in Hillsborough County, Florida. Three main areas for control of the wastewater treatment process are aeration, return and waste sludge flows, and addition of chemicals. The Falkenburg AWWTP uses oxidation ditches where both nitrification and denitrification take place simultaneously in a low dissolved oxygen, extended aeration environment. Anaerobic selectors before the oxidation ditches help control the growth of filamentous organisms and may also initiate biological phosphorus removal. The addition of aluminum sulfate for chemical phosphorus removal ensures phosphorus permit limits are met. Wasting is conducted by maintaining a desired mixed liquor suspended solids (MLSS) concentration in the oxidation ditches. For this study, activated sludge modeling was used to construct and calibrate a model of the plant. This required historical data to be collected and compiled, and supplemental sampling to be carried out. Kinetic parameters were adjusted in the model to achieve simultaneous nitrification-denitrification. A sensitivity analysis found maximum specific growth rates of nitrifying organisms and several half saturation constants to be influential to the model. Simulations were run with the calibrated model to observe relationships between sludge age, MLSS concentrations, influent loading, and effluent nitrogen concentrations. Although the case-study treatment plant is meeting discharge permit limits, there are several recommendations for improving operation performance and efficiency. Controlling wasting based on a target MLSS concentration causes wide swings in the sludge age of the system. Mixed liquor suspended solids concentration is a response variable to changes in sludge age and influent substrate. Chemical addition for phosphorus removal should also be optimized for cost savings. Finally, automation of aeration control using online analyzers will tighten control and reduce energy usage.

Increasing pressure is being placed on the dairy industry to reduce nitrogen losses from soil. Nitrification inhibitors are a management strategy that could be implemented on dairy farms to help reduce losses of nitrogen. Nitrification inhibitors work by temporarily inhibiting the microbial conversion of soil ammonium to nitrate. Past trials have indicated that nitrification inhibitors can increase grass production and decrease nitrate leaching; however, little is known about the long-term effects on other soil nitrogen processes such as denitrification. Denitrification rates in soils can be limited by the availability of substrate (carbon and nitrate) and by insufficient anaerobic microsites. The objective of this thesis was to establish whether the nitrification inhibitor, dicyandiamide (DCD), could decrease denitrification rates in dairy farm soils by limiting nitrate availability. A field trial was established at Dexcel's research farm near Hamilton, New Zealand on a Typic Orthic Allophanic Soil. Twenty replicated field plots were established in a paddock, ten plots acted as controls and ten plots had DCD applied to the soil once a month at a rate of 30 kg ha-1 yr-1. Denitrification rates were measured using the acetylene inhibition technique on intact soil cores. Ammonium and nitrate concentration, soil carbon availability, denitrifying enzyme activity and soil pH were measured from soil samples collected monthly. Two further field experiments and one laboratory experiment were undertaken. The distribution of denitrifying enzyme activity with soil depth was measured to ensure that the depth to which denitrification was sampled (15 cm) in the field experiment was sufficient. DCD degradation in the field during 20 days was measured to establish how long the effects of DCD might last. A laboratory study investigated whether DCD would decrease denitrifying enzyme activity in soil, when soil conditions were optimized for denitrification. More than 80% of the denitrifying enzyme activity occurred in the top 15 cm of the soil profile, indicating that the depth to which samples were collected was sufficient. There was no significant decrease in denitrification rates in the field experiment when DCD was added. Nitrification was partially inhibited as shown by a significant increase in soil ammonium (+14%) and a significant decline in soil nitrate (-17%) in the DCD-amended soils compared to the control soils. However, the decline in soil nitrate was not great enough for nitrate to limit denitrification. Nitrate concentrations were consistently greater than 5 mg NO3- kg-1 soil (the proposed threshold for declines in denitrification). The laboratory study supported the field study with DCD having no effect on denitrifying enzyme activity and nitrate concentrations remaining above 5 mg NO3- kg-1 soil. So while DCD reduced nitrification rates and the formation of nitrate, denitrification rates were not limited by nitrate availability. DCD was completely degraded in the soil 19 days after DCD application, with a half-life of 2.9 days, which may be a reason for the minor inhibition of nitrification. Denitrifying enzyme activity, carbon availability and soil pH were all unaffected by the application of DCD.

Aquatic sediments are the recipients of a continual rain of organic debris from the water column. The decomposition reactions within the sediment and the rates of material exchange between the sediment and water column are critically moderated by the transport processes within the sediment. The sediment and solute movement induced by burrowing animals – bioturbation and bioirrigation – far exceed abiotic transport processes such as sedimentation burial and molecular diffusion. Thalassinidean shrimp are particularly abundant burrowing animals. Living in high density populations along coastlines around the world, these shrimp build complex burrow networks which they actively maintain and irrigate.¶ I used a laser scanner to map thalassinidean shrimp (Trypaea australiensis) mound formation. These experiments measured rapid two-way exchange between the sediment and depth. Subduction from the sediment surface proved to be just as important as sediment expulsion from depth, yet this is not detected by conventional direct entrapment techniques. The experiments demonstrated that a daily sampling frequency was needed to capture the extent of the two-way exchange.¶ I derived a one-dimensional non-local model accounting for the excavation, infill and collapse (EIC) of burrows. Maximum likelihood analyses were used to test the model against 210Pb and 228Th profiles taken from sediment cores in Port Phillip Bay, Melbourne. The maximum likelihood approach proved to be a useful technique for quantifying parameter confidence bounds and allowing formal comparison with a comparable biodiffusion model. The EIC model generally outperformed the biodiffusion model, and in all cases best EIC model parameter estimates required some level of burrow infill with surface material. The EIC model was expanded to two and three dimensions, which allowed the representation of lateral heterogeneity resulting from the excavation, infill and collapse of burrow structures. A synthetic dataset generated by the two-dimensional model was used to demonstrate the effects of heterogeneity and core sampling on the mixing information that can be extracted from one-dimensional sediment core data.¶ Burrow irrigation brings oxygenated water into burrow depths, and can affect the nitrogen cycle by increasing the rates of coupled nitrification and denitrification reactions. I modelled the nitrogen chemistry in the annulus of sediment surrounding an irrigated burrow using a radially-symmetrical diffusion model. The model was applied to three published case studies involving thalassinidean shrimp experiments and to field data from Port Phillip Bay. The results highlighted divergences between current theoretical understanding and laboratory and field measurements. The model further demonstrated potential limitations of measurements of burrow characteristics and animal behaviour in narrow laboratory tanks. Activities of burrowing animals had been hypothesised to contribute to high denitrification rates within Port Phillip Bay. Modelling work in this thesis suggests that the model burrow density required to explain these high denitrification rates is not consistent with the sampled density of thalassinidean shrimp in the Bay, although dense burrows of other animals are likely to be important. Limitations of one-dimensional representations of nitrogen diagenesis were explored via comparisons between one-dimensional models and the full cylinder model.

Bioelectrochemical systems couple the oxidation of an electron donor at the anode with the reduction of an electron acceptor at the cathode, using microorganisms to catalyse one or both reactions. When the overall reaction is exergonic, a power output is generated and the system is referred to as microbial fuel cell (MFC); when power is added to the system and hydrogen is produced at the cathode through electrolysis of water, the system is referred to as microbial electrolysis cell (MEC). This PhD thesis is principally focused on the microbial fuel cells technology. Microbial fuel cells are regarded as a sustainable technology for electric energy generation from the oxidation of organic substrates contained in wastewater. The rising need for renewable energy sources and sanitation has encouraged intense research in this novel technology. Nevertheless, up untill now the interest has been primarily focused on the anodic oxidation of organic matter contained in wastewater. However, in addition to organics, wastewater also contains other pollutants, such as soluble nitrogen compounds, for which specific treatment is required. In conventional wastewater treatment systems, the organics available in the wastewater are typically used as electron donor during denitrification. However, a considerable fraction (>50%) of the chemical oxygen demand (COD) is still oxidized aerobically due to the large recirculation flows from the nitrification to the denitrification stages required in anoxic/aerobic configurations to allow for low nitrate levels in the final effluent. This increased COD demand is normally fulfilled by supplementary COD addition, with consequent increase of treatment costs. Alternatively, microorganisms can use inorganic carbon substrates and inorganic electron donors such as hydrogen for denitrification. However, the use of compressed hydrogen is hampered by its low solubility. As a solution, electrochemical hydrogen production permits in situ delivery of the electron donor and is advantaged by simplified control and dissolution of H2. The energy requirements to provide reducing power for denitrification can be decreased if bacteria use the electrode directly as electron donor without intermediate hydrogen production in bioelectrochemical systems. However, fundamental knowledge on bioelectrochemical denitrification is still lacking, therefore, this PhD thesis aims to fill some of these knowledge gaps and to solve some of the bottlenecks of the use of biocathodes. In particular, the goals of this work are: (i) to produce a suitable microbial community able to use the cathode as the sole electron donor during denitrification; (ii) to engineer a bioelectrochemical system able to couple the cathodic denitrification with the oxidation of organics at the anode; (iii) to characterize and quantify the electron losses during anodic and cathodic processes; (iv) to develop a bioelectrochemical system that maximises the nitrogen removal by integrating the nitrification stage into the cathode; finally, (v) to provide an insight into the structural properties of the biofilm performing nitrogen removal at the cathode. The results reveal that microbes can effectively utilize the electrode as electron donor for nitrate reduction to gaseous nitrogen at a redox potential that excludes intermediate production of hydrogen. Measurements revealed that acetoclastic methanogenesis and bacterial growth were responsible for causing the major electron losses at the anode. Adjusting the anodic potential did not achieve a significant overall reduction of the electron losses. At the cathode, the charge transfer efficiencies were instead very high, with the losses only due to the generation of nitrous oxide. Moreover, adjustments of the cathode potential resulted in higher efficiency. High carbon and nitrogen removal was obtained with a COD demand for denitrification as low as 2.4 g per g nitrogen denitrified, which is much lower than typically observed in heterotrophic–based nitrogen removal technologies (>7 g g 1). Nitrogen was removed at rates up to 0.256 kg N m-3 d-1, which is comparable to other autotrophic denitrification processes. Simultaneous nitrification and denitrification was observed in a combined system with cathodic aeration, at bulk dissolved oxygen (DO) levels up to 5 mg L-1, which is considerably higher than normally considered feasible for the process. Confocal laser scanning microscope analysis revealed the existence of a structured biofilm where putative nitrifying organisms occupied the outer layers in contact with the aerated bulk liquid, and putative denitrifying organisms occupy the layers closer to the electrode. These findings are significant in the field of bioelectrochemical systems as they help to unravel some of the complex questions relating to biocathodes. Additionally, the system provides an attractive option to achieve a very high level of nitrogen removal from wastewater with low COD/N ratios due to the selective utilisation of the COD for the denitrification reaction via the electrical transfer of reducing equivalents from the anode to the cathode. However, this research creates new questions, particularly regarding the mechanisms of electron transfer at the cathode. Also a number of practical design and optimisation challenges need to be overcome before wider applications can be considered.

L'objectif principal de ce travail a porté sur l'optimisation du dimensionnement et de la gestion des installations de traitement des eaux usées par boues activées fonctionnant à basse température (10-12°C) et soumise à une contrainte de traitement poussé sur l'azote. Dans ce but, nous avons étudié la faisabilité de la nitrification à des charges massiques stabilisées supérieures à 0.1 kgDBO5.(kgMVS.j)-1. Le fonctionnement d'une installation pilote alimentée par un effluent synthétique, puis par un effluent urbain réel, a été étudié pour différentes charges massiques stabilisées à une température de 11 +/- 1°C. Les résultats très détaillés acquis en continu sur deux périodes de six mois ont suggéré le rôle et la hiérarchie des facteurs influençant la capacité de nitrification. Ils ont permis d'adapter l'outil de simulation dynamique Activated Sludge Model n°1 (ASM1). La double démarche expérimentale et numérique mise en oeuvre a permis de dégager les rôles des conditions de fonctionnement (âge des boues, charge volumique en azote, durée de présence d'oxygène) et des propriétés de l'effluent à traiter (ratios caractéristiques, part des différentes fractions) sur les performances de traitement de l'azote et sur la composition de la boue. Les valeurs limites des paramètres de gestion (charge massique maximale, durée d'aération journalière), permettant à différentes configurations d'installation (bassin unique, réacteur avec zone d'anoxie en tête) de respecter une concentration en azote total inférieure à 10 mgN/L dans le rejet, ont pu être dégagées. Des stratégies de gestion dans le cas de variations de flux importantes en entrée d'installation (cas des zones touristiques de montagnes) ont pu être évaluées (fonctionnement à charge massique variable par adaptation de la durée d'aération, ou bien utilisation d'un bassin d'aération à volume variable).

<p>Two ecological models of nitrogen processes in treatment wetlands have been evaluated and compared. These models have been implemented, simulated, and visualized in the Modelica language. The differences and similarities between the Modelica modeling environment used in this thesis and other environments or tools for ecological modeling have been evaluated. The modeling tools evaluated are PowerSim, Simile, Stella, the MathModelica Model Editor, and WEST. </p><p>The evaluation and the analysis have been performed using McCall’s factors for software quality (McCall et al, 1977), a correlation analysis and the Constant Comparative Method (Glaser&Strauss, 1999). The results show that the modeling tools and the models can both be separated into two categories: Simple Components and Complex Components for the modeling tools, and Simple Models and Complex Models for the models. The major difference between the Simple Components and the Complex Components is the higher possibility of the Complex Components to create and reuse separate components and the higher complexity in these components. The similarities between the categories are that they are consistent, easy to overview and use, if no new components are to be created. The major difference between the Simple Models and the Complex models lies in the number of functions and in the possibility of reuse and expansion. The similarities between all the models are that they are all consequent, logical, valid, specialized, and easy to use if the user has programming skill. </p><p>To conclude thisthesis, the nitrogen decrease in a constructed treatment wetland can well be simulated using the Nitrification/Denitrification model expressed in Modelica and the MathModelica Model Editor. However, some changes to the Model Editor are recommended to make the creation of the model easier. The most important of these changes are the addition of a tutorial, the ddition of useful error handling and messages, and the removal of unnecessary Visio features.</p>

Research performed at the Division of Environmental Microbiology has over the last years resulted in the isolation of possible bacterial key-organisms with efficient nutrient removal properties (Comamonas denitrificans, Brachymonas denitrificans, Aeromonas hydrophila). Effective use of these organisms for enhanced nutrient removal in wastewater treatment applications requires the strains to be retained, to proliferate and to maintain biological activity within theprocess. This can be achieved by immobilization of the organisms using an appropriate system.Two putative immobilization systems, agar entrapment and biofilm formation, wereassessed. Surface attached biofilm growth provided better results with respect to cell retention,proliferation and microbial activity than immobilization in agar beads. Thus, biofilm physiology was further characterized using simplified systems of single, dual or multi strain bacterial consortia containing the key-organisms as well as other wastewater treatment isolates. Mechanisms for initial adherence, biofilm formation over time, dynamics and characteristics of extracellular polymeric substances (EPS) and exopolysaccharides, nutrient removal activity as well as the effect of bacterial interactions were investigated. The results showed that all theassessed bacterial strains could form single strain biofilm providing that a suitable nutrientsupply was given. Production of EPS was found to be critical for biofilm development and both EPS and polysaccharide residue composition varied with bacterial strain, culture conditions and biofilm age. Denitrification and phosphorus removal activity of the keyorganisms was maintained in biofilm growth. Co-culturing of two or more strains resulted in both synergistic and antagonistic effects on biofilm formation as well as the microbial activitywithin the biofilm. Bacterial interactions also induced the synthesis of new polysaccharideswhich were not produced in pure strain biofilms.The complexity of single and mixed strain biofilm development and the implications of interactions on biofilm performance were underlined in this study. The data presented can be useful for modeling of biofilm systems, serve as a tool for selection of bacterial strain combinations to use for bioaugmentation/bioremediation or provide a base for further experiment design. / QC 20100622

Bacteria play important roles in the transformation of nutrients in wetlands, but few studies have examined parameters affecting variation in bacterial community composition between wetlands. We compared the composition of eubacterial and denitrifying bacterial biofilm communities in 32 agricultural constructed wetlands in southern Sweden, and the extent to which wetland environmental parameters could explain the observed variation. Structure and richness of the eubacterial 16S rRNA gene and three denitrifying bacterial enzyme genes (nirK, nirS and nosZ), analysed by molecular fingerprinting methods, varied among the constructed wetlands, which could be partly explained by different environmental parameters. Results from the enzyme gene analyses were also compared to determine whether the practice of using a single denitrifying bacterial gene could characterize the overall community composition of denitrifying bacteria. We found that nirK was more diverse than both nirS and the nosZ, and the band structure and richness of the three genes were not related to the sam environmental parameters. This suggests that using a single enzyme gene may not suffice to characterize the community composition of denitrifying bacteria in constructed agricultural wetlands. / <p>Included in doctoral thesis: Milenkovski, Susann. Structure and Function of Microbial Communities in Constructed Wetlands - Influence of environmental parameters and pesticides on denitrifying bacteria. Lund University 2009.</p>

No description available.

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.