Littérature scientifique sur le sujet « Denitrification processe »

Mixotrophic denitrification has showed great potential for treating wastewater with a low C/N ratio. Mixotrophic denitrification is the process combining autotrophic denitrification and heterotrophic denitrification in one system. It can compensate the disadvantage of the both denitrifications. Instead of using sodium acetate and glucose as carbon source for the heterotrophic denitrification, agriculture solid wastes including rice straw (RS), wheat straw (WS), and corncob (CC) were employed in this study to investigate their potential as carbon source for treating low C/N wastewater. The carbon releasing pattern of the three carbon rich materials has been studied as well as their capacity in denitrification. The results showed that the highest denitrification occurred in the corncob system which was 0.34 kg N/(m3·d). Corncob was then selected to combine with sulfur beads to build the mixotrophic denitrification system. The reactor packed with sulfur bead on the top and corncob on the bottom achieved 0.34 kg N/(m3·d) denitrification efficiency, which is higher than that of the reactor packed with completely mixed sulfur bead and corncob. The autotrophic denitrification and heterotrophic denitrification were 42.2% and 57.8%, respectively. The microorganisms in the sulfur layer were Thermomonas, Ferritrophicum, Thiobacillus belonging to autotrophic denitrification bacteria. Kouleothrix and Geothrix were mostly found in the corncob layer, which have the function for fiber hydrolysis and denitrification. The study has provided an insight into agriculture solid waste application and enhancement on denitrification of wastewater treatment.

This study investigated operational performance and microbial communities in the integrated acidification-denitrification bioreactor and the followed methanogenesis process. Industrial wastewater, cassava stillage (CS) was used as the carbon source amended with or without nitrate. The results showed that acidification and denitrification could occur simultaneously in a single acidification-denitrification reactor, and denitrificatoin did not suppress the acidogenic activity. Both denitrification and DNRA could contribute to nitrate reduction and proportions of them were about 60% and 40% respectively at the tested condition of COD/NO3-Nof 50. The introduction of nitrate into acidogenic phase did not have any effect on the followed methanogenic process. Microbial communities sampled from two systems were analyzed by culture-independent techniques based on PCR-DGGE. The relative abundance of acid-producing bacteria (primarily Parabacteroides distasonis and Chloroflexi) in the nitrate-amended reactor further confirmed that the addition of nitrate did not suppress the activity of acid-producing bacteria. Bacteria involved in denitrification and DNRA were also detected. The archaeal communities in methanogenic reactors of two systems showed no significant differences. And Methanoculleus and Methanolobus were the dominant bacteria in the culture.

We found anoxic zones in aerated activated sludge flocs, and demonstrated denitrification under normal operating conditions. Sulfate reduction was not found. Micro-environments and microbial conversions in flocs from bulking and non-bulking activated sludge were determined with microsensors for H2S, O2, NO2− and NO3−. Denitrification and sulfate reduction rates were mmeasured with 15N- and 35S-tracer techniques. We showed that under normal reactor conditions (ca. 20% air saturation) anoxic zones develop within flocs allowing denitrification. The denitrification rates amounted to 40% of the rates under anoxic conditions. At 100% air saturation no anoxic zones were found and no denitrification occurred. However, in flocs from bulking sludge (at 20% air saturation) anoxic zones were absent and denitrification did not occur. In bulking sludge only at total anoxia was denitrification found. Confocal microscopy showed that flocs from bulking sludge were much looser than those from non-bulking sludge. The absence of anoxic zones and of denitrification was attributed to the open floc structure, allowing advective oxygen transport. Sulfate reduction was not detected in any of the sludges tested by microsensors or by tracer techniques even under anoxic conditions. this indicates that the sulfur cycle (sulfate reduction and sulfide oxidation) does not play a role in mineralization processes and bulking in activated sludge. Preliminary molecular work (in situ hybridization with the 16S-rRNA probe SRB385) indicated the presence of small amounts of sulfate reducing bacteria in all sludges. Either the probe is not specific or the sulfate reducers present are not active under reactor conditions.

An unusually high concentration of nitrate (NO3) ranging between 291 and 6790 mg/L (as N) was observed during a review of solute data for brine samples from the inland Sabkha Matti. A multi-tracer approach considering water chemistry, stable nitrate isotopes (δ15N and δ18O), and the radioactive isotope of hydrogen (tritium, 3H) was utilized to evaluate the nitrate sources and transformation in this hydrogeological setting. The results suggested that the source of the high nitrate levels is related to a leakage from a manure/septic system near the proximal eastern edge of the Sabkha. Moreover, the impact of Sabkha’s characteristics on biological denitrifications was evaluated in this study. The results suggest that denitrification was not a major process in Sabkha Matti. Several factors may contribute to the limitation of denitrification on the brine samples including high dissolved oxygen contents, high salinity and chloride.

National and international regulations require a minimum nitrogen removal efficiency of 70% in most public sewage treatment plants. Unlike in activated sludge plants, selective denitrification in trickling filters was not possible until now. Therefore the aim was to employ trickling filter plants for selective denitrification, using innovative technology that involved minimum capital expenditure. For selective denitrification, it is necessary to prevent as much as possible the transfer of oxygen into the trickling filter while feeding the nitrate to be removed, a process similar to upstream denitrification in the activated sludge process. In a test operation conducted in several sewage treatment plants for over a year, the new process with selective denitrification in a covered trickling filter has given successful results. The denitrification efficiency of this system is comparable to that of upstream denitrification in the activated sludge process. Thus, selective denitrification in the trickling filter is a practical alternative to other nitrogen removal processes, while maintaining the established advantages offered by the trickling filter process.

Mature landfill leachate is a complex and highly polluted effluent with a large amount of ammonia nitrogen, toxic components and low biodegradability. Its COD/N and BOD5/COD ratios are low, which is not suitable for traditional nitrification and denitrification processes. Anaerobic ammonia oxidation (anammox) is an innovative biological denitrification process, relying on anammox bacteria to form stable biofilms or granules. It has been extensively used in nitrogen removal of mature landfill leachate due to its high efficiency, low cost and sludge yield. This paper reviewed recent advances of anammox based processes for mature landfill leachate treatment. The state of the art anammox process for mature landfill leachate is systematically described, mainly including partial nitrification–anammox, partial nitrification–anammox coupled denitrification. At the same time, the microbiological analysis of the process operation was given. Anaerobic ammonium oxidation (anammox) has the merit of saving the carbon source and aeration energy, while its practical application is mainly limited by an unstable influent condition, operational control and seasonal temperature variation. To improve process efficiency, it is suggested to develop some novel denitrification processes coupled with anammox to reduce the inhibition of anammox bacteria by mature landfill leachate, and to find cheap new carbon sources (methane, waste fruits) to improve the biological denitrification efficiency of the anammox system.

For the sewage treatment plants near rivers and closed water bodies in urbanized areas there is a growing demand for introduction of advanced treatment processes for nitrogen and phosphorus removal for water quality conservation and environmental protection. In order to achieve the total nitrogen content of below 10 mg/L in effluent, a compact single sludge pre-denitrification process by dosing immobilized pellets in the nitrification tank (PEGASUS process) has been already developed (Tanaka et al. 1992). Furthermore, a two-stage PEGASUS process and a PEGASUS process with post-denitrification were developed and investigated for nitrogen removal. Both processes achieved the total nitrogen of less than 5mg/L.

In recent years, there is a trend of low C/N ratio in municipal domestic wastewater, which results in serious problems for nitrogen removal from wastewater. The addition of an external soluble carbon source has been the usual procedure to achieve denitrification. However, the disadvantage of this treatment process is the need of a closed, rather sophisticated and costly process control as well as the risk of overdosing. Solid-phase denitrification using biodegradable polymers as biofilm carrier and carbon source was considered as an attractive alternative for biological denitrification. The start-up time of the novel process using PCL (polycaprolactone) as biofilm carrier and carbon source was comparable with that of conventional process using ceramsite as biofilm carrier and acetate as carbon source. Further, the solid-phase denitrification process showed higher nitrogen removal efficiency under shorter hydraulic retention time (HRT) and low carbon to nitrogen (C/N) ratio since the biofilm was firmly attached to the clear pores on the surface of PCL carriers and in this process bacteria that could degrade PCL carriers to obtain electron donor for denitrification was found. In addition, solid-phase denitrification process had a stronger resistance of shock loading than that in conventional process. This study revealed, for the first time, that the physical properties of the biodegradable polymer played a vital role in denitrification, and the different microbial compositions of the two processes was the main reason for the different denitrification performances under low C/N ratio.

The paper summarizes the state-of-the-art of the most recent advances in biological nitrogen removal, including process design criteria and technological innovations. With reference to the Modified Ludzck Ettinger (MLE) process (pre-denitrification and nitrification in the activated sludge process), the most common nitrogen removal process used nowadays, a new design equation for the denitrification reactor based on specific denitrification rate (SDNR) has been proposed. In addition, factors influencing SDNR (DO in the anoxic reactor; hydrodynamic behavior) are analyzed, and technological solutions are proposed. Concerning technological advances, the paper presents a summary of various “deammonification” processes, better known by their patent names like ANAMMOX®, DEMON®, CANON®, ANITA® and others. These processes have already found applications in the treatment of high-strength wastewater such as digested sludge liquor and landfill leachate. Among other emerging denitrification technologies, consideration is given to the Membrane Biofilm Reactors (MBfRs) that can be operated both in oxidation and reduction mode.

A captivating challenge for environmental catalysis is nowadays the rational design of efficient catalysts able to take on the new challenges in energy, economy, and environment sustainability of industrial processes. A catalytic structure must be developed so as to be active, stable, resistant, when working in the presence of poisons (e.g., water, sulphur), but also easily to handle and manage, non-toxic, biocompatible and bioavailable in the view of environment sustainability and circular economy. In this scenario, hydroxyapatite (HAP, Ca10(PO4)6(OH)2) has emerged as bio-material characterized by interesting properties (e.g., thermal/chemical stability, low water solubility, modest morphological properties, and intrinsic amphotericity of surface), which make it a promising support for active metal phases (e.g., Cu, Fe, Mn, Sn), giving rise to heterogeneous catalysts for reactions of industrial chemistry and environment protection. The main scope of this Thesis under the joint supervision between Università degli Studi di Milano (Italy) and Université Claude Bernard Lyon 1 (France) is to develop eco-friendly HAP-based catalysts for environmental reactions devoted to the abatement of nitrogen-containing air pollutants (NOx, NH3, and N2O). During three years of work a commercial bare HAP, coming from the NOVOSOL® process (patented procedure by Solvay), has been at first characterized to assess its applicability as support for innovative eco-friendly catalysts for air-quality protection. The used hydroxyapatite was proven to be a mesoporous, crystalline material characterized by good thermal and chemical stability. Considering that HAP possesses a multifunctional surface, whose acid and basic sites may act as anchoring centres for the immobilization of metal species, it has been properly functionalized with selected metal species, in particular Cu(II) and/or Fe(III), from nitrate precursors in different amount (1 < wt.% Me < 13), according to a wet deposition procedure (contact time of 15 min, 24 h, or 48 h, T = 40°C, calcination at 500°C for 1 h), already reported in previous studies. In this way, different series of metal loaded HAP-catalysts (mono- and bi-metallic) have been obtained, varying some parameters (i.e., metal loading, pH of the Fe-precursor solution, and time of contact between the bare HAP support and the aqueous metal solution) during the preparation. Morphology, structure, acidity, metal speciation and sitting at the HAP surface have been studied through targeted physico-chemical techniques (e.g., N2-physisorption, XRPD, NH3-titration, UV-DR, Mӧssbauer, XP, and EXAFS spectroscopies, CO adsorption at -196°C followed by FT-IR, TEM-EDX) to elucidate the main bulk and surface properties. In general, a complex scenario emerged. The copper- and/or iron-introduction onto HAP did not cause evident modifications in the sample morphology, independently on the metal nature and loading. All the samples were described by mesoporosity and only minor microporosity: they were characterized by surface area values in 60-95 m2·g-1 interval, according to the N2 adsorption/desorption isotherms collected at -196°C. Concerning copper-HAP samples, UV-DRS results indicated that the copper-phase was present in highly dispersed and isolated ions/small nanoclusters onto HAP. However, when the Cu-concentration onto HAP was higher than 6 wt.%, copper-species additionally reacted with phosphate groups at the HAP surface, giving rise to a further Cu-containing crystalline phase (libethenite, JCPDS: 00-036-0404), revealed by XRPD and TEM-EDX. Regarding iron-HAP samples, UV-DRS, Mössbauer and XPS results indicated that both isolated and aggregated Fe-species were present on all the catalyst surfaces. Eventually, the bimetallic samples were characterized by a higher dispersion of metal species than the monometallic counterparts, as revealed by NH3-titrations, TEM-EDX, and XPS analyses. Three environmental reactions have been then selected to abate NOx, NH3, and N2O: NH3-SCR, Selective Catalytic Reduction of NOx by NH3, NH3-SCO, Selective Catalytic Oxidation of NH3, and the catalytic N2O-decomposition reaction. Catalytic tests have been performed in continuous reaction lines equipped with flow reactor and inline instruments (FT-IR and µ-GC) for quantitative analysis of fed/vented gaseous species. The catalytic performances have been studied under ideal and quasi-real feeding, also evaluating the time-on-stream stability, reusability and the resistance to some poisoning species (e.g., sulphur dioxide, alkaline species) of selected samples. Copper-HAP samples have been studied in the NH3-SCR and the N2O-decomposition reaction. The observed catalytic performances under ideal- and quasi-real feeding mixtures suggested that the SCR activity was driven by the Cu-dispersion, as reported for Cu-zeolites. However, the studied Cu-HAP samples were less active than conventional Cu-based systems, even if selectivity to the desired N2 higher than 93% was obtained in the whole temperature range studied. Considering that N2O could be obtained as the undesired by-product due to the unselective NH3 oxidation by O2 for temperatures higher than 400°C in the NH3-SCR, Cu-HAP samples have been additionally studied in the N2O decomposition reaction in the view of their potential use for reducing N2O emissions in post-treatment approaches. The obtained results indicated that Cu-HAP samples can be valid alternatives to some conventional catalytic systems because they require ca. 450°C to efficiently decompose N2O. Differently from what observed in the NH3-SCR, here the catalytic activity was governed by the Cu-Cu distance, according to the reaction mechanism known for Cu-zeolites. Indeed, the most active catalyst possessed dispersed copper-species together with small Cu-aggregates, providing the ideal active sites with the optimal Cu-Cu distance. Iron-HAP catalysts have been tested in the NH3-SCR, NH3-SCO, and N2O-decomposition reactions. They showed modest catalytic performances in the studied reactions, but they remained less active than commercial Fe-based systems. However, they have been studied to evaluate their potentialities for the abatement of gaseous pollutants among the worst of our environment. The obtained results indicated that the studied environmental reactions could be also performed in a single cascade process to achieve the desired zero-emissions goal. For the cascade process, the most promising catalyst among those studied is at an average concentration of Fe (about 6–9 wt.%), to guarantee a surface composed of isolated Fe3+ ions or oligonuclear species that ensure good activity with an equally good selectivity. Eventually, bimetallic copper iron-HAP catalysts have been studied in the NH3-SCR reaction. The obtained results indicated that they were active under both dry/wet feeding, even if they remained less active than conventional bimetallic zeolites. Their activity seemed to be governed by the total metal dispersion, even if, when the catalytic performances of the bimetallic samples were compared with those of the monometallic counterparts, no clear trend of activity was identified due to the fact that the metal-phase could experience different environment, if present alone onto HAP or copresent with another one. To cut a long story short, results obtained in this Thesis enlightened the potential use of hydroxyapatite as promising eco-friendly support for environmental reactions devoted to the abatement of nitrogen-containing air pollutants (NOx, NH3, and N2O). Even if the obtained copper and/or iron hydroxyapatite-based catalysts are not as performant as the commercial catalytic systems, it seems that the suitable route to obtain ever more active and effective HAP-based catalysts is the suitable control of the surface metal distribution onto HAP that is not an easy task. In this context, also in accordance with the positive effects of these innovative HAP-based catalysts on the environment, current investigations are ongoing to develop ever more effective sustainable catalysts for air-quality protection.
Aujourd'hui un défi captivant pour la catalyse environnementale est la conception rationnelle de catalyseurs efficaces capables de relever les nouveaux défis en matière de durabilité énergétique, économique et environnementale des procédés industriels. Une structure catalytique doit être développée de manière à être active, stable, résistante, lorsqu'on travaille en présence de poisons (ex. eau, soufre), mais aussi facilement manipulable et maniable, non toxique, biocompatible et biodisponible dans l'optique de durabilité de l'environnement et économie circulaire. Dans ce scénario, l'hydroxyapatite (HAP, Ca10(PO4)6(OH)2) est apparue comme un biomatériau caractérisé par des propriétés intéressantes (par exemple, stabilité thermique/chimique, faible solubilité dans l'eau, faibles propriétés morphologiques), qui en font un support prometteur pour les phases métalliques actives (ex. Cu, Fe, Mn, Sn), donnant naissance à des catalyseurs hétérogènes pour les réactions de chimie industrielle et de protection de l'environnement. Le principal objectif de cette thèse en cotutelle entre l'Università degli Studi di Milano (Italie) et l'Université Claude Bernard Lyon 1 (France) a été de développer des catalyseurs écologiques à base d’HAP pour les réactions environnementales consacrées à la réduction de polluants de l'air contenant de l'azote (NOx, NH3 et N2O). Pendant trois ans de travail, une HAP commerciale, issue du procédé NOVOSOL® (procédé breveté par Solvay), a d'abord été caractérisée pour évaluer son applicabilité comme support de catalyseurs innovants et respectueux de l'environnement pour la protection de la qualité de l'air. L'hydroxyapatite utilisée s'est avérée être un matériau cristallin et mésoporeux caractérisé par une bonne stabilité thermique et chimique. Considérant que l’HAP possède une surface multifonctionnelle, dont les sites acides et basiques peuvent servir de centre d'ancrage pour l'immobilisation d'espèces métalliques, elle a été correctement fonctionnalisée avec des espèces métalliques sélectionnées, en particulier Cu(II) et/ou Fe(III), à partir de précurseurs de nitrate en quantité différente (1 < wt.% Me < 13), selon une procédure de dépôt par voie humide (temps de contact de 15 min, 24 h ou 48 h, T = 40°C, calcination à 500°C pendant 1 h), déjà rapporté dans de précédentes études. De cette manière, différentes séries de catalyseurs à base d’HAP chargés en métal (mono- et bi-métalliques) ont été préparés, en faisant varier les paramètres suivants: charge en métal, pH de la solution de fer, temps de contact entre le support HAP et la solution précurseur métallique. La morphologie, la structure, l'acidité, la spéciation des métaux et la fonctionalisation à la surface du HAP ont été étudiées par les techniques physico-chimiques suivantes: physisorption d’N2, XRPD, titrage par NH3, spectroscopies UV-DR, Mӧssbauer, XP et EXAFS, adsorption de CO à -196°C suivi par FT-IR et TEM-EDX afin de relier les performances catalytiques aux propriétés texturales, structurales et chimiques des solides préparés. De manière générale, les résultats montrent que l'introduction de cuivre et/ou de fer sur l’HAP ne provoque pas de modifications majeures dans la morphologie des échantillons, indépendamment de la nature du métal et de la charge. Tous les échantillons présentent des isothermes de type mésoporeux avec la présence au début de l’isotherme d’un faible volume microporeux. Les surfaces spécifiques calculées à partir du modèle BET varient entre 60 et 95 m2·g-1. En ce qui concerne les échantillons de cuivre-HAP, les résultats UV-DRS montrent que la phase de cuivre est présente sous de nanoclusters ioniques très bien dispersés et isolés sur l’HAP. Cependant, lorsque la masse de Cu sur l’HAP est supérieure à 6 %, les espèces de cuivre réagisse également avec les groupes phosphate de surface, donnant naissance à une autre phase cristalline contenant du Cu (libethenite, JCPDS: 00-036-0404), détectée par XRPD et TEM-EDX. En ce qui concerne les échantillons de Fe-HAP, les résultats UV-DRS, Mössbauer et XPS montrent que des espèces de Fe isolées et agrégées sont présentes à la surface des catalyseurs. Concernant la caractérisation des systèmes bimétalliques, les résultats montrent une dispersion plus élevée des espèces métalliques que sur les systèmes monométalliques, confirmé par des titrages par NH3 et les analyses TEM-EDX et XPS. Trois réactions environnementales ont ensuite été sélectionnées pour réduire les NOx, NH3 et N2O: la réduction catalytique sélective des NOx par NH3 (NH3-SCR), l’oxydation catalytique sélective d’NH3 (NH3-SCO), et la réaction de décomposition catalytique de l’N2O. Les tests catalytiques ont été effectués en réacteur continu équipé d'un réacteur à lit fixe et d'outils analytiques en ligne (FT-IR et µ-GC) pour l'analyse quantitative des espèces gazeuses alimentées/éventées. Les performances catalytiques ont été étudiées dans des conditions d'alimentation modéles et/ou quasi-réelles, évaluant également la stabilité, la réutilisabilité et la résistance à certaines espèces empoisonnantes (par exemple, le dioxyde de soufre, les espèces alcalines) des échantillons sélectionnés. Les échantillons de cuivre-HAP ont été étudiés dans la NH3-SCR et la réaction de décomposition de l’N2O. Les performances catalytiques observées montrent que l'activité SCR est sensible à la dispersion de Cu, comme indiqué pour les zéolithes de Cu. Cependant, les échantillons de Cu-HAP étudiés se sont révélés moins actifs que les échantillons à base de Cu conventionnels, même si une sélectivité en N2 supérieure à 93% a été obtenue dans toute la gamme de température étudiée. Considérant que le protoxyde d’azote (N2O) peut être formé en tant que sous-produit indésirable en raison de l'oxydation non sélective du NH3 par l'O2 pour des températures supérieures à 400 °C dans la NH3-SCR, des échantillons de Cu-HAP ont également été étudiés dans la réaction de décomposition de N2O en vue de leur utilisation potentielle pour prévenir la formation de N2O dans les systèmes de post-traitement. Les résultats obtenus ont indiqué que les échantillons de Cu-HAP peuvent être des alternatives valables à certains systèmes catalytiques conventionnels car ils nécessitent env. 450°C pour décomposer efficacement N2O. Contrairement à ce qui a été observé dans la NH3-SCR, ici l'activité catalytique était régie par la distance entre deux atomes de cuivre (Cu-Cu), selon le mécanisme de réaction connu pour les zéolithes Cu.8 En effet, le catalyseur le plus actif posséde des espèces de cuivre dispersées avec de petites quantités de Cu agrégées, qui permet d’obtenir une optimisation de la distance Cu-Cu. Les catalyseurs Fe-HAP ont été testés dans les réactions de NH3-SCR, de NH3-SCO et de décomposition d’N2O. Ils ont montré des performances catalytiques modestes dans les réactions étudiées, mais ils sont restés moins actifs que les systèmes commerciaux à base de Fe. Cependant, ils ont été étudiés pour évaluer leurs potentialités pour l'abattement des polluants gazeux parmi les pires de notre environnement. Les résultats obtenus ont indiqué que les réactions environnementales étudiées pouvaient également être effectuées dans un processus en cascade unique pour atteindre l'objectif de zéro émissions. Pour le procédé en cascade, le catalyseur le plus prometteur parmi ceux étudiés présente une concentration moyenne en Fe d’environ 6 à 9 % en poids, générant une surface composée d’ions Fe3+ isolés et d'espèces oligonucléaires assurant une bonne activité et une excellente sélectivité. Finalement, les catalyseurs bimétalliques Cu-Fe-HAP ont été testés dans la réaction de NH3-SCR. Les résultats obtenus indiquent qu'ils sont actifs en absence et en présence de vapeur d’eau dans le milieu réactionnel, même si ils restent moins actifs que les zéolithes bimétalliques conventionnelles. Leur activité semble être gouvernée par la dispersion métallique totale, même si, lorsque les performances catalytiques des échantillons bimétalliques ont été comparés à ceux des homologues monométalliques, aucune tendance claire de l'activité n'a été identifiée en raison du fait que la phase métallique présente un environnement différent (monométallique ou bimétallique). Les résultats obtenus dans ce travail de thèse ont permis de valider le potentiel de l’hydroxyapatite en tant que support écologique prometteur pour les applications dans le domaine de la chimie environnementale et notamment le cas de la réduction des polluants atmosphériques contenant de l'azote (NOx, NH3 et N2O). Même si les catalyseurs à base d'hydroxyapatite de cuivre et/ou de fer obtenus ne sont pas aussi performants que les systèmes catalytiques commerciaux, il semble que la voie appropriée pour obtenir des catalyseurs à base d’HAP toujours plus actifs et efficaces requiert un contrôle précis de la distribution des métaux en surface. Ce n'est pas une tâche facile. Dans ce contexte, également en accord avec les effets positifs de ces catalyseurs innovants à base d’HAP sur l'environnement, des recherches sont en cours pour développer des catalyseurs durables toujours plus efficaces pour la protection de la qualité de l'air.

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The groundwater quality has been compromised as a result of the intensification of human activities over the years. Groundwater contamination by nitrate is one of the effects of this degradation, a socio-environmental problem that affects many regions of the world and particular the city of Natal (RN). Developing techniques for nitrate removal in water is intended to eliminate or reduce the concentration of this compound, and those that involve biological processes have produced economic and environmental advantages. This study proposes a technology for biological removal of nitrate in water supply for humans, using the endocarp s coconut as a carbon source and bacteria support. The experiments were performed in pilot scale anoxic, testing different areas of the substrate surface. Results showed high rates nitrate removal during the monitoring period, noting the occurrence of denitrification after the beginning of system operation. The best performance was achieved in the treatment system containing substrate surface area increased, indicating that the decrease in the endocarp size contributed to increased bacterial activity, improving the ability to remove nitrate. About the quality analyzed aspects of water, it was found that the proposed technology has the potential water use for human consumption
A qualidade da ?gua subterr?nea vem sendo cada vez mais comprometida como consequ?ncia da intensifica??o das a??es antr?picas ao longo dos anos. Um dos efeitos dessa degrada??o ? a contamina??o dos mananciais subterr?neos por nitrato, um problema s?cio-ambiental que atinge diversas regi?es do mundo e, em particular, a cidade do Natal (RN). T?cnicas para remo??o de nitrato em ?guas t?m sido desenvolvidas a fim de eliminar, ou reduzir, a concentra??o deste composto, sendo que, as que envolvem processos biol?gicos t?m apresentado vantagens econ?micas e ambientais. Esse estudo prop?e uma tecnologia de remo??o biol?gica do nitrato em ?gua de abastecimento humano, utilizando o endocarpo de coco como fonte de carbono e suporte bacteriano. Os experimentos foram realizados em c?maras an?xicas em escala piloto, testando diferentes ?reas superficiais do substrato. Os resultados mostraram elevadas taxas de remo??o de nitrato ao longo do per?odo de monitoramento, observando a ocorr?ncia da desnitrifica??o logo ap?s o in?cio do funcionamento do sistema. O melhor desempenho foi alcan?ado no sistema de tratamento contendo substrato de maior ?rea superficial, indicando que a diminui??o no tamanho do endocarpo contribuiu com o aumento da atividade bacteriana, melhorando a capacidade de remo??o de nitrato. Quanto ? qualidade da ?gua analisada, verificou-se que a tecnologia proposta tem potencialidade de uso da ?gua para consumo humano

Aerobic denitrification is a biological nitrogen removal process in which nitrification and denitrification occur simultaneously (in the same reactor) under identical environmental conditions. This contrasts to traditional separate stage nitrification denitrification in which the nitrification and denitrification processes occur sequentially in different reactors under opposing environmental conditions. While aerobic denitrification has long been identified in other ecosystems (such as the nitrogen cycle within soil) it was not thought possible within wastewater treatment processes. The existence of aerobic denitrification within wastewater treatment systems was first identified in the early 1980's following nitrogen mass balances that suggested unexplained nitrogen losses were occurring in the aeration tanks of many full-scale biological nutrient removal facilities (total nitrogen losses of up to 30% were frequently occurring U.S.EPA (1987)). Since then researchers and engineers have attempted to elucidate the mechanics behind the aerobic denitrification phenomenon and the conditions required for its optimization. It is thought that aerobic denitrification may offer advantages and possible savings when compared to alternative traditional separate stage nitrification denitrification processes. The use of real time parameters such as ORP, pH, DO and airflow rate (oxygen demand) can provide immediate insight into a biological treatment process. This knowledge can be used to ensure optimum performance in terms of real time pollutant concentrations and hydraulic loads. This research aimed to elucidate some operational aspects of the aerobic denitrification phenomenon, to investigate opportunities for several types of real time control (ORP, pH, DO, and airflow), and to develop a process control system using the online parameters. An activated sludge process was established within two lab-scale sequencing batch reactors. The reactors were operated under a range of conditions using raw domestic wastewater as the feed. ORP, pH, DO, and airflow were measured online in real time while other biochemical parameters (such as the various forms of nitrogen) were measured periodically using HACH photometric procedures. Dissolved oxygen concentration was the operational variable (dissolved oxygen set points (DOSP) 4.0-0.5 mg/L), other parameters such as MLSS concentration and feed strength were maintained (where possible) at a consistent value (~3000 mg/L and ~600 mg/L COD respectively). The system was operated under both nitrification and aerobic denitrification conditions with the dissolved oxygen concentration determining the degree to which aerobic denitrification existed (~40% TN removal at DOSP 0.5 mg/L). The biochemical event of interest was the depletion of ammonia nitrogen. The key online profiles of interest were the ORP-time profile and the pH-time profile. The research sought to demonstrate the credibility of ORP and pH as real time control parameters for the depletion of ammonia nitrogen in the aerobic denitrification process. To achieve this a microprocessor-software based process control system was developed by using the relationship between online measurements and biochemical events. The results indicated the ORP-time profile does not provide any feature for the depletion of ammonia nitrogen when the dissolved oxygen is maintained at a fixed concentration. That is the previously identified "ammonia elbow" is probably the result of dissolved oxygen concentration breakthrough rather than nutrient depletion. The lack of an ammonia depletion elbow meant that ORP could not be used for process control within the aerobic denitrification process. The pH-time profile showed an "ammonia valley" feature at the point of ammonia depletion. This feature was consistently present in both the nitrification and aerobic denitrification processes. The research incorporated the feature into the process control system and successfully used it to control the length of the aerobic denitrification treatment sequence. With respect to elucidating some operational aspects of the aerobic denitrification phenomenon the main variable of interest was the dissolved oxygen concentration. The results indicated the aerobic denitrification process has an optimum dissolved oxygen concentration around but probably below 0.5 mg/L. The process probably does not have an optimum concentration but an optimum range. It is likely this range is influenced by variables such as the biomass concentration and the release of reducing power in terms of the ability to hydrolyze stored carbon polymers. A secondary objective of this research was to elucidate advantages of aerobic denitrification relative to alternative traditional separate stage nitrification denitrification processes. For example it has been proposed that aerobic denitrification may require smaller treatment reactors, require less air for nitrification, produce less sludge per unit of wastewater treated (relative to a traditional nitrification-denitrification process), and have less dependence on organic carbon for denitrification. The results suggested the low dissolved oxygen concentrations required for the aerobic denitrification process significantly inhibit the nitrification process. This causes a considerable extension in the required aeration times for the oxidation of ammonia nitrogen (~300% increase in aeration time relative to a traditional nitrification process). The longer aeration times suggest the process may not offer savings in terms of aeration requirements (aerobic denitrification required ~200% more air per unit of wastewater treated relative to a traditional nitrification process) or treatment tank sizes (relative to traditional separate stage processes). A reduction in the quantity of sludge produced (per unit of wastewater treated) of over 30% was demonstrated for the aerobic denitrification process. While aerobic nitrogen removal has been achieved under certain conditions autotrophically by other researchers this work found the process is probably undertaken predominantly by heterotrophic micro-organisms. The low dissolved oxygen concentrations required for the process also appear to favor heterotrophic denitrification using stored intracellular carbon (biosorption). This research demonstrated the aerobic denitrification process was able to remove nitrogen with less dependence on organic carbon (the organic carbon requirements for aerobic denitrification were not quantified but experimental data suggests a possible 40% saving) either by the use of a shortened nitrification-denitrification pathway and/or the ability to use stored carbon.

La present tesi es basa en l'estudi dels processos de bioremediació com a tecnologies de descontaminació d'aqüífers.
Concretament, es pretén estudiar la desnitrificació i la decloració reductiva com a tecnologies de bioremediació per eliminar, respectivament, els nitrats i els hidrocarburs alifàtics clorats (o CAHs, de chlorinated aliphatic hydrocarbons) de les aigües subterrànies contaminades. A més, es pretén aplicar tecnologies avançades que permetin millorar en el coneixement d'aquests processos.
L'aqüífer associat a la riera d'Argentona, situat a Argentona (Espanya), ha estat la zona d'estudi per tal d'investigar el procés de desnitrificació. En primer lloc, s'han dut a terme experiments en batch amb aigua subterrània i sòl subsuperficial del mencionat aqüífer. A partir d'aquests primers estudis, s'ha observat la baixa capacitat de l'aqüífer per eliminar els nitrats de manera natural, però alhora s'ha vist la viabilitat d'aplicar un procés de bioremediació com és l'addició de matèria orgànica. Paral·lelament, s'ha estudiat la influència de diferents factors com ara la presència d'oxigen i la tipologia de donador d'electrons sobre el procés de desnitrificació.
Posteriorment, s'ha desenvolupat un model matemàtic per descriure el consum d'oxigen, de nitrats i de matèria orgànica per part de la població microbiana facultativa i heterotròfica present en el material d'aqüífer. Alguns paràmetres del model han estat calibrats i s'ha estudiat la qualitat d'aquests paràmetres. El model desenvolupat constitueix una primera aproximació per tal d'obtenir un model de desnitrificació in situ.
Per tal d'avançar en l'estudi del procés de desnitrificació en condicions naturals, s'han realitzat experiments en dinàmic simulant el flux d'aigua subterrània a través de l'aqüífer. L'eficiència d'injectar matèria orgànica en aquestes condicions s'ha demostrat.
Paral·lelament, s'han estudiat els efectes hidrodinàmics de l'aplicació de la bioremediació i, els resultats han demostrat la importància de dissenyar acuradament les tecnologies de bioremediació a escala de camp. Per altra banda, s'ha descrit la desnitrificació en condicions dinàmiques integrant en un model matemàtic les reaccions bioquímiques i els processos de transport que tenen lloc a la columna experimental.
Finalment, s'han aplicat les noves tecnologies de biologia molecular per entendre els efectes de l'aplicació d'un procés de bioremediació a nivell microbià. Per una banda, l'aplicació de la tècnica de la reacció en cadena de la polimerasa a temps real (o real-time PCR, de real-time polymerase chain reaction) ha demostrat el creixement de la població microbiana i, concretament, de la població desnitrificant en el material d'aqüífer estimulat. Per altra banda, l'electroforesi en gel de gradient desnaturalitzant (o DGGE, de denaturing gradient gel electrophoresis) ha permès investigar els canvis en la població microbiana indígena del material d'aqüífer a causa de l'estimulació amb matèria orgànica.
Amb l'objectiu d'avançar en el coneixement dels processos de bioremediació en aigües subterrànies, s'ha estudiat també la decloració reductiva de CAHs. En aquest cas, s'han aplicat metodologies experimentals destinades a l'estudi de la posible aplicació d'una barrera reactiva permeable per eliminar una ploma que conté majoritàriament cis-1,2-dicloroetilè i clorur de vinil, i que flueix cap al riu Zenne, prop de la ciutat de Brussel·les (Bèlgica).
L'estudi ha inclòs experiments en batch per tal d'investigar el potencial degradatiu del material d'aqüífer i dels propis sediments del riu Zenne. Així mateix, també s'han dut a terme experiments en columna que simulaven el flux d'aigua subterrània a través dels sediments del riu o del material d'aqüífer. Els resultats han demostrat el gran potencial degradatiu dels sediments, que a la llarga es podrien potenciar com a biobarrera natural del sistema per tal de prevenir que les aigües contaminades arribin a l'aigua superficial del riu Zenne.
This thesis is based on the study of bioremediation processes as reliable technologies to remove contaminants from groundwater.
Specifically, it is aimed to study denitrification and reductive dechlorination as bioremediation technologies to remove nitrates and chlorinated aliphatic hydrocarbons (CAHs), respectively, from polluted groundwater. In addition, it is aimed to apply advanced technologies which allow improving on the knowledge of these processes.
The aquifer associated to the Stream Argentona, located in Argentona, Catalunya (Spain), was selected as study site to investigate the denitrification process. In the first part, microcosm experiments containing groundwater and subsoil from the aquifer were performed. From these first studies it was observed the low capacity of the aquifer to eliminate nitrates under natural conditions, but, at the same time, it was noted the feasibility of applying a bioremediation process such as the addition of organic matter. In addition, the influence of different factors such as the presence of oxygen and the type of electron donor on the denitrification process was studied.
Afterwards, a mathematical model was developed to explain the microbiological processes that occur when stimulating the aquifer material with an organic carbon source. The model could successfully explain the consumption of oxygen, nitrates and organic matter by the indigenous facultative heterotrophic microbial population from aquifer. Some parameters of the model were calibrated from experimental data and the quality of these parameters was investigated. The developed model constitutes a first approach in order to have reliable models for in situ denitrification.
In order to advance in the study of the denitrification process in natural conditions, dynamic experiments were carried out simulating the groundwater flow through the aquifer. The efficiency of injecting organic matter under these conditions was demonstrated. At the same time, hydrodynamic effects of the process were observed, indicating the importance to design properly bioremediation technologies before its application in field-scale. Furthermore, an integrated model coupling the biochemical reactions and the transport processes inside the column was developed and applied to describe denitrification under dynamic conditions.
Finally, molecular microbiological techniques were applied to investigate microbial changes due to the application of enhanced denitrification. On the one hand, real-time polymerase chain reaction (real-time PCR) assays revealed the growth of microbial population, specially of denitrifying bacteria in aquifer material stimulated with an organic carbon source. On the other hand, the denaturing gradient gel electrophoresis (DGGE) method allowed to investigate changes in the indigenous microbial community due to the amendment with organic matter.
In order to advance in the knowledge of bioremediation processes in groundwater, reductive dechlorination of CAHs in groundwater was studied. In this case, experiments at laboratory scale were applied, aimed to study the possible application of a permeable reactive barrier (PRB) to eliminate a CAH-contaminated plume, containing basically cis-1,2-dichloroethene and vinyl chloride, which flows to the River Zenne near Brussels, Belgium.
The study included batch experiments in order to investigate the degradation potential in aquifer and sediments of the River Zenne, as well as column experiments which simulated the groundwater flow through the sediments of the river or the aquifer material. The results demonstrated the high degradation potential of the sediments, which in the long term could be enhanced to act as a natural biobarrier of the system in order to prevent groundwater contaminants from arriving at the surface water of the River Zenne.

It is crucial to study the denitrification process driven by bacteria as it is one of the most important environmental processes for several reasons: i) it has an application in the removal of nitrogen (N) from high-N waste materials ii), it is one of the mechanisms to N-fertilizer¿s loss, iii) it contributes to the emissions of gasses with large global warming potential, and iv) it is the mechanism by which the global nitrogen cycle is balanced. Many models have been developed in the framework of continuous models to deal with the complexity of the denitrification process in order to become predictive models, but some of the assumptions contained in them are not realistic enough in those contexts, and also they have their own constraints and limitations. On the other hand, the researchers have paid more attention to the role of microbial activity with the advance of experimental techniques. Discrete models, such as individual-based models (IBMs), can be developed and applied to microbial systems due to the fact that they allow representation of some intracellular characteristics regarding the complexity of the micro-organisms, which constitutes a key advantage of this modelling approach in the study of the different biotechnological processes. The IBM is able to incorporate and accommodate the behaviour of denitrifying bacteria, and investigate their metabolism from different and attractive perspectives. A key factor in modelling the microbial activity is the methodology followed to represent metabolic pathways. A cellular metabolic model could be based on a non-equilibrium thermodynamic approach such as the Thermodynamic Electron Equivalents Model (TEEM), which is developed for biomass yield prediction using the associated standard Gibbs free energies and the bioenergetics growth efficiency between cell anabolism and catabolism. The main objective of this doctoral thesis is to develop an IBM to study denitrification processes driven by denitrifying bacteria, using TEEM to write microbial metabolic reactions (MMRs) which represent the metabolic pathways as the center of the individual sub-model. Two new computational models of the INDISIM family, INDISIM-Paracoccus and INDISIM-Denitrification have been designed, implemented on the NetLogo platform, parameterized and calibrated with experimental data to analyze the system dynamics in a bioreactor in batch and continuous culture with denitrifying bacteria growing in it. The bioreactor conditions can be aerobic and/or anaerobic, and the growing media is liquid medium with an electron donor, C-source, N-source, and oxygen and all N-oxides as electron acceptors. An open access and open source tool has been developed to write MMRs based on TEEM. It is called MbT-tool which stands for Metabolism-based on Thermodynamics. Using MbT-Tool three sets of MMRs have been written, which are the centre of the individual sub-model for INDISIM-Paracoccus and INDISIM-denitrification, representing reactions involved in: i) cellular maintenance, ii) individual mass synthesis, and iii) individual mass degradation to reduce cytotoxic products. The simulation results obtained with INDISIM-Paracoccus and INDISIM-Denitrification have been compared with experimental data published by Felgate et al. (2012) regarding the growth of Paracoccus denitrificans and Achromobacter xylosoxidans in a bioreactor. According to the statistical analysis of the simulations results, for both denitrifying bacteria tested, the IBMs developed show better adjustments in the assays with electron donor limited than in the assays with electron acceptor limited.
L’estudi del procés de desnitrificació és rellevant, ja que és un important procés mediambiental, a causa que: i) és un dels mecanismes que ocasiona una pèrdua dels fertilitzants de nitrogen (N), ii) és d’utilitat en l’eliminació de N en residus amb un alt contingut en N, iii) contribueix en les emissions de gasos d’alt potencial sobre l’escalfament global, i iv) és el mecanisme pel qual es tanca el cicle del N. S’han desenvolupat diversos models continus per tractar la complexitat del procés de desnitrificació en sistemes ambientals per tal de que puguin ser models amb capacitat predictiva, però alguns dels supòsits que es fan no són prou realistes i tenen les seves mancances i limitacions. D’altra banda, els investigadors estan posant més atenció en el rol que juga l’activitat microbiana, des de que en els darrers anys s’ha desenvolupat i avançat en tècniques experimentals de manera important. Models discrets, com els models basats en l’individu (IBMs), poden ser desenvolupats i utilitzats en sistemes microbians ja que permeten la representació d’algunes característiques intracel·lulars atenent a la complexitat dels microorganismes, cosa que resulta clau a l’hora d’abordar aquest nou enfoc per l’estudi de diversos processos biotecnològics. Els IBMs són capaços d’incorporar el comportament de les bactèries desnitrificants i d’investigar el seu metabolisme des de perspectives diferents. Un factor clau en la modelització de l’activitat microbiana és la metodologia seguida per a representar les rutes metabòliques. Un model de metabolisme cel·lular podria estar basat en l’enfoc de la termodinàmica de no-equilibri, com per exemple el denominat Model Termodinàmic d’Electrons Equivalents (TEEM). TEEM va ser desenvolupat per predir el rendiment de la biomassa utilitzant les energies lliures estàndards de Gibbs associades i l’eficiència bioenergètica de creixement entre els processos anabòlics i catabòlics de la cèl·lula. L’objectiu principal d’aquesta tesis doctoral és desenvolupar un IBM per l’estudi dels processos de desnitrificació duts a terme per bactèries desnitrificants, mitjançant l’ús del TEEM per descriure les reaccions metabòliques microbianes (MMRs) que representen les vies metabòliques i són el centre del sub-model individual. Dos nous models computacionals de la família d’INDISIM, l’INDISIM-Paracoccus i l’INDISIM-Denitrification han estat dissenyats, implementats en la plataforma de NetLogo, i parametritzats i calibrats amb dades experimentals per analitzar la dinàmica d’un sistema format per bactèries desnitrificants en un bioreactor en un cultiu tancat i/o continu, en condicions aeròbies i/o anaeròbies. El medi de cultiu és líquid i conté un donador d’electrons, oxigen i òxids de N com acceptors d’electrons, una font de carboni i una de N. S’ha creat una eina d’accés i codi obert per escriure les MMRs basades en el TEEM i és anomenada MbT-tool (Metabolisme basat en la Termodinàmica). Utilitzant MbT-tool es poden descriure tres grups de MMRs, que seran el centre del sub-model individual per l’INDISIM-Paracoccus i l’INDISIM-denitrification, i que són reaccions involucrades en: i) el manteniment cel·lular, ii) la síntesi individual de massa, i iii) la degradació individual de massa per reduir els productes citotòxics. Els resultats de simulació obtinguts amb INDISIM-Paracoccus i INDISIM-Denitrification han estat comparats amb les dades experimentals publicades per Felgate et al. (2012), sobre el creixement de Paracoccus denitrificans i Achromobacter xylosoxidans en un bioreactor. Segons l’anàlisi estadístic dels resultats, per les dues bactèries desnitrificants amb les quals s’ha testat, els IBMs desenvolupats mostren millors ajustos en els assajos amb donadors d’electrons limitants que en els assajos amb acceptors d’electrons limitants. El desenvolupament d’un IBM i la seva aplicació amb cert nivell de detall i complexitat intracel·lular constitueix una avantatge per la investigació de la desnitrificació bacterià.
Es relevante estudiar la desnitrificación ya que es un importante proceso medioambiental, debido a que: i) es uno de los mecanismos que explica la pérdida de fertilizantes de nitrógeno (N), ii) tiene aplicación en la remoción de N proveniente de residuos con alto contenido de N, iii) contribuye a las emisiones de gases que presentan gran potencial de calentamiento global, y iv) es el mecanismo por el cual se balancea el ciclo del N. Varios modelos han sido desarrollados usando el enfoque de la modelización continua para hacer frente a la complejidad del proceso de la desnitrificación, con la finalidad de obtener modelos predictivos, pero algunas de sus suposiciones no son suficientemente reales en este contexto, además estos modelos tienen sus propias restricciones y limitaciones. Por otro lado, los investigadores están prestando más atención al rol de la actividad microbiana, desde que en los últimos años se han desarrollado y avanzado las técnicas experimentales de manera importante. Modelos discretos, como los modelos-basados en el individuo (IBMs), pueden ser desarrollados y aplicados a sistemas microbianos ya que permiten representar algunas de las características intracelulares relacionadas con la complejidad de los microorganismos, lo cual constituye una ventaja clave de este enfoque de modelización en el estudio de diversos procesos biotecnológicos. El IBM es capaz de incorporar y adaptar el comportamiento de las bacterias desnitrificantes e investigar su metabolismo desde perspectivas distintas. Un factor clave para modelizar la actividad microbiana es la metodología utilizada para representar las rutas metabólicas. Un modelo metabólico celular puede estar basado en la termodinámica del no equilibrio como el Modelo Termodinámico de Electrones Equivalentes (TEEM), el cual está desarrollado para la predicción del rendimiento de la biomasa usando las energías estándar de Gibbs junto con la eficiencia bioenergética de crecimiento entre anabolismo y catabolismo celular. El objetivo principal de esta tesis doctoral es desarrollar un IBM para estudiar la desnitrificación bacteriana, usando el TEEM para escribir reacciones metabólicas microbianas (MMRs) las cuales representan a las rutas metabólicas y son el centro del sub-modelo individual. Dos nuevos modelos computacionales de la familia INDISIM, el INDISIM-Paracoccus y el INDISIM-Denitrification, han sido diseñados, implementados en la plataforma NetLogo, parametrizados y calibrados con datos experimentales para estudiar la dinámica del crecimiento de las bacterias desnitrificantes dentro de un bioreactor en cultivos cerrados y continuos, en condiciones aerobias o anaerobias. El medio de cultivo es líquido y contiene un donador de electrones, oxígeno y los óxidos de N como aceptores de electrones, una fuente de carbono y una fuente de N. Una herramienta de acceso libre y código abierto ha sido desarrollada para escribir las MMRs basadas en TEEM y es llamada MbT-Tool (Metabolismo basado en la Termodinámica). Utilizando MbT-Tool se pueden escribir tres grupos de MMRs que han sido el centro del sub-modelo individual para INDISIM-Paracoccus e INDISIM-Denitification, y que representan las reacciones involucradas en: i) el mantenimiento celular, ii) la síntesis de masa individual, y iii) la degradación de la masa individual para reducir productos citotóxicos. Los resultados de simulación obtenidos con INDISIM-Paracoccus e INDISIMDenitrification han sido comparados los datos experimentales publicados por Felgate et al. (2012) relacionados con el crecimiento de Paracoccus denitrificans y Achromobacter xylosoxidans dentro de un bioreactor. De acuerdo con el análisis estadístico de los resultados de simulación, los IBMs desarrollados muestran mejores ajustes para los experimentos con donador de electrones limitado que para los ensayos con aceptor de electrones limitado. El desarrollo y aplicación de IBMs con algunos detalles y complejidad intracelular, constituyen una ventaja clave en la investigación y comprensión de los diferentes pasos de la desnitrificación bacteriana.

PGPR bacteria include taxonomically diverse bacterial species that function for improving plant mineral nutrition, stress tolerance, and disease suppression. A number of PGPR are being developed and commercialized as soil and seed inoculants, but to date, their interactions with resident bacterial populations are still poorly understood, and-almost nothing is known about the effects of soil management practices on their population size and activities. To this end, the original objectives of this research project were: 1) To examine microbial community interactions with plant-growth-promoting rhizobacteria (PGPR) and their plant hosts. 2) To explore the factors that affect PGPR population size and activity on plant root surfaces. In our original proposal, we initially prqposed the use oflow-resolution methods mainly involving the use of PCR-DGGE and PLFA profiles of community structure. However, early in the project we recognized that the methods for studying soil microbial communities were undergoing an exponential leap forward to much more high resolution methods using high-throughput sequencing. The application of these methods for studies on rhizosphere ecology thus became a central theme in these research project. Other related research by the US team focused on identifying PGPR bacterial strains and examining their effective population si~es that are required to enhance plant growth and on developing a simulation model that examines the process of root colonization. As summarized in the following report, we characterized the rhizosphere microbiome of four host plant species to determine the impact of the host (host signature effect) on resident versus active communities. Results of our studies showed a distinct plant host specific signature among wheat, maize, tomato and cucumber, based on the following three parameters: (I) each plant promoted the activity of a unique suite of soil bacterial populations; (2) significant variations were observed in the number and the degree of dominance of active populations; and (3)the level of contribution of active (rRNA-based) populations to the resident (DNA-based) community profiles. In the rhizoplane of all four plants a significant reduction of diversity was observed, relative to the bulk soil. Moreover, an increase in DNA-RNA correspondence indicated higher representation of active bacterial populations in the residing rhizoplane community. This research demonstrates that the host plant determines the bacterial community composition in its immediate vicinity, especially with respect to the active populations. Based on the studies from the US team, we suggest that the effective population size PGPR should be maintained at approximately 105 cells per gram of rhizosphere soil in the zone of elongation to obtain plant growth promotion effects, but emphasize that it is critical to also consider differences in the activity based on DNA-RNA correspondence. The results ofthis research provide fundamental new insight into the composition ofthe bacterial communities associated with plant roots, and the factors that affect their abundance and activity on root surfaces. Virtually all PGPR are multifunctional and may be expected to have diverse levels of activity with respect to production of plant growth hormones (regulation of root growth and architecture), suppression of stress ethylene (increased tolerance to drought and salinity), production of siderophores and antibiotics (disease suppression), and solubilization of phosphorus. The application of transcriptome methods pioneered in our research will ultimately lead to better understanding of how management practices such as use of compost and soil inoculants can be used to improve plant yields, stress tolerance, and disease resistance. As we look to the future, the use of metagenomic techniques combined with quantitative methods including microarrays, and quantitative peR methods that target specific genes should allow us to better classify, monitor, and manage the plant rhizosphere to improve crop yields in agricultural ecosystems. In addition, expression of several genes in rhizospheres of both cucumber and whet roots were identified, including mostly housekeeping genes. Denitrification, chemotaxis and motility genes were preferentially expressed in wheat while in cucumber roots bacterial genes involved in catalase, a large set of polysaccharide degradation and assimilatory sulfate reduction genes were preferentially expressed.