Impact of antibiotics and particulate matter from wastewater discharges on the abundance of antibiotic resistance genes in river sediments

In der vorliegenden Arbeit wurde der Zusammenhang zwischen der Einleitung von kommunalen Kläranlagen und der Menge an Antibiotikaresistenzgenen (ARG) in Flusssedimenten des Vorfluters untersucht. Eine wesentliche Frage war dabei, was der Treiber für die Akkumulation der ARG ist. Zur Auswahl standen dabei die Einleitungen von Antibiotikarückständen (ABs) auf der einen Seite oder die partikuläre Fracht auf der anderen Seite. Letztere ist dafür bekannt, pathogene Organismen aber auch ARG mit sich zu führen. Die Ergebnisse einer Feldstudie zeigten zunächst, dass die Selektion von ARG durch Antibiotikarückstände möglicherweise weniger entscheidend ist, als allgemein angenommen wird. Stattdessen wiesen sie auf die zweite der oben benannten Optionen für die Verbreitung von ARG hin: ARG (ermB, blaTEM, tetM, qnrS) assoziieren zum Teil stark mit den partikulären Bestandteilen im Abwasser und gelangen damit über die Sedimentation in das Sediment der Vorfluter. Die ARG-Menge in der sedimentierbaren Fraktion von Abwasser (Genkopien pro g Schwebstoffe, engl. total suspended solids, TSS) korrelierte dabei positiv mit der Änderung der ARG-Menge im Flusssediment des Vorfluters (Differenz der Genkopien pro g Sediment unterhalb und oberhalb der Einleitungsstelle) (R² = 0,93; p < 0,05). Jährlich werden mehrere hundert Tonnen an partikulären Bestandteilen aus dem untersuchten Klärwerk in den Vorfluter eingeleitet. Ca. 50 % davon kann sich unmittelbar hinter der Einleitungsstelle absetzen. Scheinbar ist die Sedimentation dieser Masse entscheidend für die Verbreitung von ARG im Flusssediment und führt zu einer Erhöhung um 0,5 – 2 Zehnerpotenzen. Um die Dynamik des oben beschriebenen Sedimentationsprozesses besser zu verstehen, wurde im nächsten Schritt eine Partikelfraktion aus kommunalem Abwasser extrahiert (durch Sieben und Filtration) und in Batchreaktoren gegeben, welche zuvor mit natürlichen Flusssedimenten und Leitungswasser befüllt wurden. Parallel hierzu wurden ABs (Erythromycin, Tetrazyklin, Ciprofloxacin, Roxithromycin, Penicillin V und Sulfamethoxazol) hinzugegeben, um sie auf ihre Fähigkeit zur Selektion von ARG zu testen. Die Entwicklung der Häufigkeit von sechs ARGs (ermB, tetM, blaTEM, sul1, CTX-M-32 und qnrS) und die Gesamtzahl an Bakterien (16S rDNA) wurde in der Wasserphase und im Sediment über einen Zeitraum von zwei Monaten verfolgt. Trotz der relativ hohen Konzentration an ABs, welche über den gesamten Zeitraum auf konstantem Niveau gehalten wurde (5 μg/L), blieb die Häufigkeit der ARG unverändert. Die Zugabe von Abwasserpartikeln führte zu einem sofortigen, starken Anstieg an ARG in der Wasserphase (3 – 5 Zehnerpotenzen) und im Sediment (1 – 4 Zehnerpotenzen). Erhöhte ARG-Mengen gingen allerdings mit einem bestimmten und vollständigen Zerfall einher. Die Ergebnisse sowohl aus dem Feldversuch als auch aus den gezielten Versuchen im Labor zeigen, dass die erhöhte Häufigkeit an ARG in Vorflutern durch den kontinuierlichen Eintrag von ARG aus Klärwerksabläufen verursacht wird. Sie lassen zudem vermuten, dass ARG nicht persistieren, wenn dieser Eintragspfad unterbrochen wird

Scalability of Localized Arc Filament Plasma Actuators

Temporal flow control of a jet has been widely studied in the past to enhance jet mixing or reduce jet noise. Most of this research, however, has been done using small diameter low Reynolds number jets that often have little resemblance to the much larger jets common in real world applications because the flow actuators available lacked either the power or bandwidth to sufficiently impact these larger higher energy jets. The Localized Arc Filament Plasma Actuators (LAFPA), developed at the Ohio State University (OSU), have demonstrated the ability to impact a small high speed jet in experiments conducted at OSU and the power to perturb a larger high Reynolds number jet in experiments conducted at the NASA Glenn Research Center. However, the response measured in the large-scale experiments was significantly reduced for the same number of actuators compared to the jet response found in the small-scale experiments. A computational study has been initiated to simulate the LAFPA system with additional actuators on a large-scale jet to determine the number of actuators required to achieve the same desired response for a given jet diameter. Central to this computational study is a model for the LAFPA that both accurately represents the physics of the actuator and can be implemented into a computational fluid dynamics solver. One possible model, based on pressure waves created by the rapid localized heating that occurs at the actuator, is investigated using simplified axisymmetric simulations. The results of these simulations will be used to determine the validity of the model before more realistic and time consuming three-dimensional simulations are conducted to ultimately determine the scalability of the LAFPA system

Developing an Empirical Model for Jet-Surface Interaction Noise

The process of developing an empirical model for jet-surface interaction noise is described and the resulting model evaluated. Jet-surface interaction noise is generated when the high-speed engine exhaust from modern tightly integrated or conventional high-bypass ratio engine aircraft strikes or flows over the airframe surfaces. An empirical model based on an existing experimental database is developed for use in preliminary design system level studies where computation speed and range of configurations is valued over absolute accuracy to select the most promising (or eliminate the worst) possible designs. The model developed assumes that the jet-surface interaction noise spectra can be separated from the jet mixing noise and described as a parabolic function with three coefficients: peak amplitude, spectral width, and peak frequency. These coefficients are fit to functions of surface length and distance from the jet lipline to form a characteristic spectra which is then adjusted for changes in jet velocity and/or observer angle using scaling laws from published theoretical and experimental work. The resulting model is then evaluated for its ability to reproduce the characteristic spectra and then for reproducing spectra measured at other jet velocities and observer angles; successes and limitations are discussed considering the complexity of the jet-surface interaction noise versus the desire for a model that is simple to implement and quick to execute

Including Finite Surface Span Effects in Empirical Jet-Surface Interaction Noise Models

The effect of finite span on the jet-surface interaction noise source and the jet mixing noise shielding and reflection effects is considered using recently acquired experimental data. First, the experimental setup and resulting data are presented with particular attention to the role of surface span on far-field noise. These effects are then included in existing empirical models that have previously assumed that all surfaces are semi-infinite. This extended abstract briefly describes the experimental setup and data leaving the empirical modeling aspects for the final paper

LES of a Jet Excited by the Localized Arc Filament Plasma Actuators

The fluid dynamics of a high-speed jet are governed by the instability waves that form in the free-shear boundary layer of the jet. Jet excitation manipulates the growth and saturation of particular instability waves to control the unsteady flow structures that characterize the energy cascade in the jet.The results may include jet noise mitigation or a reduction in the infrared signature of the jet. The Localized Arc Filament Plasma Actuators (LAFPA) have demonstrated the ability to excite a high-speed jets in laboratory experiments. Extending and optimizing this excitation technology, however, is a complex process that will require many tests and trials. Computational simulations can play an important role in understanding and optimizing this actuator technology for real-world applications. Previous research has focused on developing a suitable actuator model and coupling it with the appropriate computational fluid dynamics (CFD) methods using two-dimensional spatial flow approximations. This work is now extended to three-dimensions (3-D) in space. The actuator model is adapted to a series of discrete actuators and a 3-D LES simulation of an excited jet is run. The results are used to study the fluid dynamics near the actuator and in the jet plume

Low Frequency Noise Contamination in Fan Model Testing

Aircraft engine noise research and development depends on the ability to study and predict the noise created by each engine component in isolation. The presence of a downstream pylon for a model fan test, however, may result in noise contamination through pylon interactions with the free stream and model exhaust airflows. Additionally, there is the problem of separating the fan and jet noise components generated by the model fan. A methodology was therefore developed to improve the data quality for the 9 15 Low Speed Wind Tunnel (LSWT) at the NASA Glenn Research Center that identifies three noise sources: fan noise, jet noise, and rig noise. The jet noise and rig noise were then measured by mounting a scale model of the 9 15 LSWT model fan installation in a jet rig to simulate everything except the rotating machinery and in duct components of fan noise. The data showed that the spectra measured in the LSWT has a strong rig noise component at frequencies as high as 3 kHz depending on the fan and airflow fan exit velocity. The jet noise was determined to be significantly lower than the rig noise (i.e., noise generated by flow interaction with the downstream support pylon). A mathematical model for the rig noise was then developed using a multi-dimensional least squares fit to the rig noise data. This allows the rig noise to be subtracted or removed, depending on the amplitude of the rig noise relative to the fan noise, at any given frequency, observer angle, or nozzle pressure ratio. The impact of isolating the fan noise with this method on spectra, overall power level (OAPWL), and Effective Perceived Noise Level (EPNL) is studied

Validation of the Small Hot Jet Acoustic Rig for Jet Noise Research

The development and acoustic validation of the Small Hot Jet Aeroacoustic Rig (SHJAR) is documented. Originally conceived to support fundamental research in jet noise, the rig has been designed and developed using the best practices of the industry. While validating the rig for acoustic work, a method of characterizing all extraneous rig noise was developed. With this in hand, the researcher can know when the jet data being measured is being contaminated and design the experiment around this limitation. Also considered is the question of uncertainty, where it is shown that there is a fundamental uncertainty of 0.5dB or so to the best experiments, confirmed by repeatability studies. One area not generally accounted for in the uncertainty analysis is the variation which can result from differences in initial condition of the nozzle shear layer. This initial condition was modified and the differences in both flow and sound were documented. The bottom line is that extreme caution must be applied when working on small jet rigs, but that highly accurate results can be made independent of scale

Acoustic Efficiency of Azimuthal Modes in Jet Noise Using Chevron Nozzles

The link between azimuthal modes in jet turbulence and in the acoustic sound field has been examined in cold, round jets. Chevron nozzles, however, impart an azimuthal structure on the jet with a shape dependent on the number, length and penetration angle of the chevrons. Two particular chevron nozzles, with 3 and 4 primary chevrons respectively, and a round baseline nozzle are compared at both cold and hot jet conditions to determine how chevrons impact the modal structure of the flow and how that change relates to the sound field. The results show that, although the chevrons have a large impact on the azimuthal shape of the mean axial velocity, the impact of chevrons on the azimuthal structure of the fluctuating axial velocity is small at the cold jet condition and smaller still at the hot jet condition. This is supported by results in the azimuthal structure of the sound field, which also shows little difference in between the two chevron nozzles and the baseline nozzle in the distribution of energy across the azimuthal modes measured

Effect of Turbulence Modeling on an Excited Jet

The flow dynamics in a high-speed jet are dominated by unsteady turbulent flow structures in the plume. Jet excitation seeks to control these flow structures through the natural instabilities present in the initial shear layer of the jet. Understanding and optimizing the excitation input, for jet noise reduction or plume mixing enhancement, requires many trials that may be done experimentally or computationally at a significant cost savings. Numerical simulations, which model various parts of the unsteady dynamics to reduce the computational expense of the simulation, must adequately capture the unsteady flow dynamics in the excited jet for the results are to be used. Four CFD methods are considered for use in an excited jet problem, including two turbulence models with an Unsteady Reynolds Averaged Navier-Stokes (URANS) solver, one Large Eddy Simulation (LES) solver, and one URANS/LES hybrid method. Each method is used to simulate a simplified excited jet and the results are evaluated based on the flow data, computation time, and numerical stability. The knowledge gained about the effect of turbulence modeling and CFD methods from these basic simulations will guide and assist future three-dimensional (3-D) simulations that will be used to understand and optimize a realistic excited jet for a particular application