Добірка наукової літератури з теми "Microbial electrochemical snorkel"

In anaerobic sediments, microbial degradation of petroleum hydrocarbons is limited by the rapid depletion of electron acceptors (e.g., ferric oxide, sulfate) and accumulation of toxic metabolites (e.g., sulfide, following sulfate reduction). Deep-sea sediments are increasingly impacted by oil contamination, and the elevated hydrostatic pressure (HP) they are subjected to represents an additional limitation for microbial metabolism. While the use of electrodes to support electrobioremediation in oil-contaminated sediments has been described, there is no evidence on their applicability for deep-sea sediments. Here, we tested a passive bioelectrochemical system named ”oil-spill snorkel” with two crude oils carrying different alkane contents (4 vs. 15%), at increased or ambient HP (10 vs. 0.1 MPa). Snorkels enhanced alkanes biodegradation at both 10 and 0.1 MPa within only seven weeks, as compared to nonconductive glass controls. Microprofiles in anaerobic, contaminated sediments indicated that snorkels kept sulfide concentration to low titers. Bulk-sediment analysis confirmed that sulfide oxidation by snorkels largely regenerated sulfate. Hence, the sole application of snorkels could eliminate a toxicity factor and replenish a spent electron acceptor at increased HP. Both aspects are crucial for petroleum decontamination of the deep sea, a remote environment featured by low metabolic activity.

Constructed wetland-microbial electrochemical snorkel (CW-MES) systems, which are short-circuited microbial fuel cells (MFC), have emerged as a novel tool for wastewater management, although the system mechanisms are insufficiently studied in process-based or environmental contexts. Based on quantitative polymerase chain reaction assays, we assessed the prevalence of different nitrogen removal processes for treating nitrate-rich waters with varying cathode materials (stainless steel, graphite felt, and copper) and sizes in the CW-MES systems and correlated them to the changes of N2O emissions. The nitrate and nitrite removal efficiencies were in range of 40% to 75% and over 98%, respectively. In response to the electrochemical manipulation, the abundances of most of the nitrogen-transforming microbial groups decreased in general. Graphite felt cathodes supported nitrifiers, but nirK-type denitrifiers were inhibited. Anaerobic ammonium oxidation (ANAMMOX) bacteria were less abundant in the electrochemically manipulated treatments compared to the controls. ANAMMOX and denitrification are the main nitrogen reducers in CW-MES systems. The treatments with 1:1 graphite felt, copper, plastic, and stainless-steel cathodes showed higher N2O emissions. nirS- and nosZI-type denitrifiers are mainly responsible for producing and reducing N2O emissions, respectively. Hence, electrochemical manipulation supported dissimilatory nitrate reduction to ammonium (DNRA) microbes may play a crucial role in producing N2O in CW-MES systems.

La concentration excessive de nitrates dans les eaux est due à l'utilisation d'engrais azotés dans l'agriculture et peut avoir des conséquences environnementales négatives, telles que l'eutrophisation des eaux de surface, l'augmentation des émissions de N₂O (un gaz à effet de serre) ou la toxicité de l'eau pour la faune aquatique [1]. L'une des solutions proposées pour réduire la quantité de nitrates dans l'eau est la construction de zones humides - des systèmes d'ingénierie qui utilisent les processus naturels tels que la végétation, les sédiments et les bactéries des zones humides pour aider à traiter les eaux usées [2]. Cependant, cette approche peut ne pas être assez rapide, surtout dans les périodes où la concentration de nitrates est élevée et dans les zones humides de taille insuffisante. Cette thèse explore des stratégies pour accélérer la réduction des nitrates. La réaction de dénitrification nécessite un donneur d'électrons, qui peut être du carbone organique. Ces composés apparaissent davantage dans les sédiments, alors que le nitrate est présent dans l'eau. Nous avons donc émis l'hypothèse que l'augmentation de l'interface sédiment/eau faciliterait l'accès aux donneurs d'électrons et accélérerait la dénitrification, ce que nous avons évalué dans la première partie de ce travail. Une manière de relier les sources d’électron dans les sédiments aux ions nitrates était de mettre en œuvre un système bioélectrochimique. Le système exploré dans cette thèse est un tuba électrochimique microbien, qui consiste en une seule pièce d'électrode, immergée dans deux milieux différents, ici les sédiments et l’eau. Dans le sédiment, un biofilm anodique peut être développé sur l’électrode, qui oxyde la matière organique. Les électrons sont transportés vers la partie se trouvant dans l'eau, où un biofilm cathodique se développe et le processus de réduction se produit. Les accepteurs d'électrons peuvent être ici l'oxygène ou le nitrate. L'un des objectifs de ce travail est de créer les conditions dans lesquelles le tuba électrochimique avec partie biocathodique réduisant les nitrates est développée et de caractériser ses propriétés bioélectrochimiques, la communauté microbienne de son biofilm et l'efficacité de la réduction des nitrates. Le chapitre 1 présente une revue de la littérature sur les biocathodes pour réduction des nitrates. Le chapitre 2 décrit les matériaux et méthodes utilisés dans ce travail. Le chapitre 3 décrit la zone humide artificielle et étudie l'effet de l'augmentation de l'interface eau/sédiment sur la réduction des nitrates et explore à partir d’un modèle les conséquences de l’amélioration des performances en dénitrification dans la zone humide de Rampillon.Le chapitre 4 couvre les études préliminaires du tuba électrochimique: le choix des matériaux de l'électrode et la proportion entre la partie dans l'eau et dans les sédiments. De plus, le développement du système est confirmé par des analyses électrochimiques ainsi que par l'étude de la communauté microbienne. L'ajout de nitrate provoque alors l'augmentation du courant cathodique et le déplacement du potentiel. Les résultats obtenus en laboratoire ont été comparés aux résultats obtenus sur le terrain. Cette expérience a été suivie par la construction d'un autre tuba électrochimique avec une taille d'électrodes plus importante et une configuration optimisée (chapitre 5). Cette expérience conduit à une nette augmentation de la vitesse de réduction des nitrates en lien avec les réponses électrochimiques. Une étude de l’écologie de ces biocathodes a alors été menée pour identifier les microorganismes en lien avec ces performances.Enfin, le dernier chapitre de ce travail est consacré à l’exploration du rôle d’électrodes dans les sédiments sur la réduction des nitrates
The exceeded nitrate concentration in water is caused by the use of nitrogen fertilizers in agriculture and may result in negative environmental consequences. One of the solutions are constructed wetlands – wastewater treating engineered systems. However, this approach might not be fast enough, especially in periods when nitrate concentration is high and in not sufficiently big wetlands. This thesis is exploring strategies for accelerating nitrate reduction. The denitrification requires an electron donor, such as organic carbon. These compounds appear more in the sediment, while nitrate is present in water, hence we hypothesized that increasing the sediment/water interface will facilitate the access to electron donors and accelerate denitrification, and we evaluated this in the first part of this work. Other strategy to increase this interface was to implement a bioelectrochemical system (BES) with nitrate-reducing biocathode. The BES we studied is a Microbial Electrochemical Snorkel (MES), which consists of one piece of electrode immersed in two different media, here in sediment and water. On the part in sediment an anodic biofilm is developed, which is oxidizing the organic matter. The electrons are then transported to the part of electrode in water, where the cathodic biofilm grows and the reduction of oxygen or nitrate process occurs.This work aims to create the conditions for developing MES with nitrate-reducing biocathodic part and to characterize its electrochemical properties, microbial community and nitrate reduction efficiency. A literature review about the nitrate-reduction biocathodes is provided in Chapter 1. Chapter 2 describes the materials and methods used in this work. Chapter 3 explores the effect of increasing the water/sediment interface on nitrate reduction. To increase this interface, sediment was arranged vertically in the tubes made of water-permeable tissue. This experiment was first performed in stationary state and by increasing the interface area 10 times, the nitrate reduction was increased up to 6.5 times. The volume of the sediment, its origin and composition, did not have a significant influence on nitrate reduction. This experiment was later repeated in flow, which resulted in 3.5 times faster nitrate reduction, stable for 53 days. The scenario of applying this method in the constructed wetland is considered.Chapter 4 covers the preliminary studies of MES: the choice of electrode materials and the ratio between part in water and sediment. The development of MES is confirmed by electrochemical analysis and study of microbial community. The addition of nitrate caused the increase of cathodic current and shift of potential. The laboratory results were compared with the results on the field.Next, MES of increased size and optimized distribution between sediment and water was built (Chapter 5), which confirmed the improvement in nitrate reduction. An increase of cathodic current was observed after addition of nitrate, and it decreased after nitrate was reduced. This current was linked to electron transfer reaction occurring at relatively high potentials when compared to the literature. Microbial analysis showed the significant differences between the community on biocathodes and in sediment and water.The final chapter is exploring potential role of electrodes in sediments for accelerating nitrate removal. It was implemented by integrating electrode in vertical sediment tubes that were studied in Chapter 3. Stainless steel and carbon felt electrodes were tested, and the latter caused indeed fast nitrate reduction. However, additional experiments showed that the mechanism is not nitrate reduction on the electrode. Carbon felt in sediment caused the release of species and the rapid nitrate reduction occurring in water. Changing the water eliminated the advantage in nitrate reduction. But, clear electrochemical reaction could still be observed at the electrode in sediment after nitrate addition