Sarah Gucker

Perspectives on the Interaction of Plasmas With Liquid Water for Water Purification

Plasma production or plasma injection in liquid water affords one the opportunity to nonthermally inject advanced oxidation processes into water for the purpose of purification or chemical processing. Such technology could potentially revolutionize the treatment of drinking water, as well as current methods of chemical processing through the elimination of physical catalysts. Presented here is an overview of current water treatment technology, its limitations, and the future, which may feature plasma-based advanced oxidation techniques. As such, this field represents an emerging and active area of research. The role that plasma-driven water chemistry can play in addressing emerging threats to the water supply is discussed using case study examples. Limitations of conventional plasma injection approaches include limited throughput capacity, electrode erosion, and reduced process volume. At the University of Michigan, we are investigating two potential approaches designed to circumvent such issues. These include direct plasma injection using an underwater DBD plasma jet and the direct production of plasmas in isolated underwater bubbles via a pulsed electric field. These approaches are presented here, along with the results.

A Comparative Study of the Time-Resolved Decomposition of Methylene Blue Dye Under the Action of a Nanosecond Repetitively Pulsed DBD Plasma Jet Using Liquid Chromatography and Spectrophotometry

An underwater dielectric barrier discharge (DBD) plasma jet excited by a repetitively pulsed nanosecond pulsed power modulator was used to study plasma-induced decolorization of a 1.4 × 10-4 M solution of methylene blue (MB). Past plasma decolorization studies have focused on spectrophotometry as the main diagnostic to assess decomposition. Because spectrophotometry is a measure of changes in the structure of molecular color, it is not an absolute measure of decomposition. In this paper, high-pressure liquid chromatography is used in parallel with spectrophotometry for comparison purposes and to assess the degree of true decomposition. Spectrophotometry results were found to be in agreement with chromatography measurements, suggesting that, at least in the case of MB, spectrophotometry is an adequate measure of decomposition. Additionally, the utility of a dual plasma jet applicator for rapid contaminant decomposition was explored.

Towards understanding plasma formation in liquid water via single bubble studies

Plasma-in-water based technological approaches offer great potential to addressing a wide range of contaminants threatening the safety of freshwater reserves. Widespread application of plasma-based technologies, however require a better understanding of plasma formation processes in water and the nature of the plasma-driven chemistry in solution. In this paper, we survey the scope of the threat to freshwater via contamination from a variety of sources, the status of conventional treatment technologies, the promise of plasma-based water purification, and the pathway to understanding plasma formation in water through the study of single bubble breakdown physics. Plasma formation in bubbles lie at the heart of plasma formation in liquid water. We present findings from ongoing research at the University of Michigan aimed at understanding the nature of plasma formation in bubbles, which provides an avenue for not only understanding breakdown conditions, but also insight in reducing the magnitude of the breakdown voltage. These experiments also establish an approach to a standardized apparatus for the study of plasma discharges in bubbles. We also discuss approaches to controlling plasma-induced chemistry in liquid water.

An investigation of an underwater steam plasma discharge as alternative to air plasmas for water purification

An underwater steam plasma discharge, in which water itself is the ionizing media, is investigated as a means to introduce advanced oxidation species into contaminated water for the purpose of water purification. The steam discharge avoids the acidification observed with air discharges and also avoids the need for a feed gas, simplifying the system. Steam discharge operation did not result in a pH changes in the processing of water or simulated wastewater, with the actual pH remaining roughly constant during processing. Simulated wastewater has been shown to continue to decompose significantly after steam treatment, suggesting the presence of long-lived plasma produced radicals. During steam discharge operation, nitrate production is limited, and nitrite production was found to be below the detection threshold of (roughly 0.2 mg L−1). The discharge was operated over a broad range of deposited power levels, ranging from approximately 30 W to 300 W. Hydrogen peroxide production was found to scale with increasing power. Additionally, the hydrogen peroxide production efficiency of the discharge was found to be higher than many of the rates reported in the literature to date.

Plasma Production in Isolated Bubbles

The production of plasma in isolated (i.e., unattached to a physical electrode) air bubbles in liquid water is investigated. Bubble size along with bubble position relative to the pulsed high voltage electrode is considered.

Understanding the plasma and power characteristics of a self-generated steam bubble discharge

Plasma formation in a self-generated steam bubble is studied using a coaxial discharge tube with an axial powered electrode (nominal peak operating voltage 2000 V) and an external ground lead without any gas flow. The discharge is potentially attractive for water purification applications in that the production of reactive nitrogen species and the associated water acidification is avoided. The discharge was found to form after a finite delay, which is attributed to the vapor bubble formation necessary for plasma ignition. Steam bubble composition was confirmed using emission spectra. Plasma properties and power dissipated in the self-generated steam bubble were characterized using emission spectroscopy and Lissajous methods. Discharge density and gas temperature were found to vary significantly over the applied ac voltage cycle. The power dissipated as inferred from the Lissajous method was found to scale inversely with frequency over the low frequency range investigated (4 kHz and 5 kHz).

Plasma treatment of contaminated liquid water: A comparison between steam bubble and gas bubble discharge

The treatment of contaminated water with atmospheric pressure, nonequilibrium plasma in recent years has been the subject of much research. The ability of such plasmas to treat water stem from the production of radicals that are capable of rapidly oxidizing organic contaminants. A common method of producing such radicals is by producing plasma within a gas bubble (typically air) in the liquid.However, while efficiently destroying contaminants, this practice of igniting the plasma in air bubbles has the unwanted side effect of creating acidic solutions (pH of 2.0 and lower). This acidity is believed to stem from NOx radicals produced in the plasma that diffuse into the water. To circumvent this issue, a steam discharge is investigated. Presented here is a study of the effect of a steam plasma on both tap water and tap water contaminated with organic dye, quantifying changes in acidity and nitrate/nitrite concentrations in the liquid water with treatment time.

Breakdown voltage scaling relation of isolated gas bubbles in liquid water

Atmospheric pressure plasma discharges have been investigated as a means to purify contaminated water, as these discharges efficiently produce a variety of highly reactive species1. While much investigation has involved electrode-drive plasma initiation, the use of an electrode-less set up is attractive as it avoids electrode contamination. However, the breakdown of isolated bubbles in liquid water is still poorly understood. Fundamental breakdown relation may be investigated by determining the applied breakdown voltage necessary to produce plasma in bubbles of various pd, typically by changing the bubble size. Preliminary studies have seen a Paschen-like breakdown curve for isolated bubbles of various sizes2; this study examines the breakdown behavior for a parallel plate electrode set up, including time evolution of the discharge dynamics.

Quantifying the effect of plasma irradiation on internal properties of living cells

Application of dielectric barrier discharges for wound and disease therapies-plasma medicine-is one of the fastest-growing fields in non-thermal, low temperature plasma research. It remains unclear of how particles and fields produced by the plasma source induce changes internally within the cell. This effort aims to elucidate the effect of an atmospheric pressure plasma on internal properties of the cell. This effort presents plasma source conditions incident on the cell and the internal chemical changes in cell response.

Time resolved spectroscopy of an underwater dielectric barrier discharge plasma jet

Summary form only given. Atmospheric pressure plasmas in liquid water have enjoyed much attention recently due to their ability to create vast quantities of short-lived radicals, excited species, and many other highly oxidative particles that have the ability to sterilize contaminated water. These plasmas have been shown to exhibit several distinct characteristics over a power cycle. The varying physical differences are believed to correspond to significant changes in the production mechanics of important chemical species. The dynamic characteristics of these plasmas require dynamic analyses. Presented here are the results of time-resolved spectroscopy of an underwater dielectric barrier discharge plasma jet.