Atmospheric non-thermal plasma discharges for cleaning and bio-decontamination

It has been shown that non-thermal plasma has great potential for chemical oxidation and bacterial inactivation. However, the mechanism of plasma-induced oxidation and bactericidal effects is not fully understood, and optimisation of the non-thermal plasma treatment is required to improve the efficiency of this technology. This research presents an investigation into the oxidation and bio-decontamination capabilities of steady-state corona discharges and impulsive transient plasma discharges in atmospheric air. Degree of decolorisation of blue dye by plasma discharges was obtained and used for evaluation of the oxidation efficiency of these discharges. The Gram-positive and Gram-negative bacteria, Staphylococcus aureus and Escherichia coli, respectively, were used for investigation of the bio-decontamination capability of the plasma discharges. It has been shown that conditions such as air humidity, electrode topology, and voltage levels may affect the efficiency of plasma treatment.;The obtained results show that the oxidation and inactivation effects depend on the amount of charge delivered by the plasma. The charge-dependent decolorisation and inactivation rates of plasma discharge treatment, which indicate the oxidation efficiency and inactivation efficiency, were obtained and analysed. Different decolorisation and inactivation rates were achieved with various electrode topologies and energisation polarities. This study also investigated the production of reactive species by atmospheric plasma discharges. Ozone concentration was measured during the decolorisation and inactivation tests. The production of OH radicals by the plasma discharges have also been obtained in this study using terephthalic acid as the chemical probe.;The obtained results confirm that the reactive oxygen species play a major role in the plasma discharge treatment. In addition, an attempt of using TiO2 as a catalyst to enhance oxidation and bio-decontamination effects of the plasma discharge treatment has been made. TiO2 was revealed to have the potential to improve the oxidation efficiency of atmospheric plasma discharges. The results obtained and presented in this thesis will help in optimisation of non-thermal plasma systems for chemical and biological decontamination.It has been shown that non-thermal plasma has great potential for chemical oxidation and bacterial inactivation. However, the mechanism of plasma-induced oxidation and bactericidal effects is not fully understood, and optimisation of the non-thermal plasma treatment is required to improve the efficiency of this technology. This research presents an investigation into the oxidation and bio-decontamination capabilities of steady-state corona discharges and impulsive transient plasma discharges in atmospheric air. Degree of decolorisation of blue dye by plasma discharges was obtained and used for evaluation of the oxidation efficiency of these discharges. The Gram-positive and Gram-negative bacteria, Staphylococcus aureus and Escherichia coli, respectively, were used for investigation of the bio-decontamination capability of the plasma discharges. It has been shown that conditions such as air humidity, electrode topology, and voltage levels may affect the efficiency of plasma treatment.;The obtained results show that the oxidation and inactivation effects depend on the amount of charge delivered by the plasma. The charge-dependent decolorisation and inactivation rates of plasma discharge treatment, which indicate the oxidation efficiency and inactivation efficiency, were obtained and analysed. Different decolorisation and inactivation rates were achieved with various electrode topologies and energisation polarities. This study also investigated the production of reactive species by atmospheric plasma discharges. Ozone concentration was measured during the decolorisation and inactivation tests. The production of OH radicals by the plasma discharges have also been obtained in this study using terephthalic acid as the chemical probe.;The obtained results confirm that the reactive oxygen species play a major role in the plasma discharge treatment. In addition, an attempt of using TiO2 as a catalyst to enhance oxidation and bio-decontamination effects of the plasma discharge treatment has been made. TiO2 was revealed to have the potential to improve the oxidation efficiency of atmospheric plasma discharges. The results obtained and presented in this thesis will help in optimisation of non-thermal plasma systems for chemical and biological decontamination

Investigation of methods for reducing aflatoxin contamination in distillers grains

The overall goal of this project was to reduce the aflatoxin level in the final coproduct of ethanol bioprocessing--DDGS. This was pursued by examining the effects of reduction of aflatoxin in the incoming corn prior to bioprocessing, the degradation of aflatoxin in the intermediate products, namely DWG and CDS, during processing, and aflatoxin degradation in the DDGS. Segregation techniques (size screening and density sorting) and detoxification methods (conventional and microwave heating, food additives, and high voltage atmospheric cold plasma) were evaluated for their effectiveness in aflatoxin reduction. Effectiveness of physical segregation of aflatoxin contaminated corn was investigated by size screening and density sorting in a 737 kg corn lot with an aflatoxin level of 185 ppb. There are statistically significant differences in major and minor diameters, the sphericities and the densities between moldy and healthy corn kernels. The moldy corn kernels had a smaller major diameter, greater sphericity and a lower density. Results indicated that removal of fine material from the corn lot through size screening could significantly reduce aflatoxin in the remaining lot. Further removal of small size kernels through cleaning with a screen cleaner and removal of lower density kernels with a gravity table gave an additional reduction of aflatoxin in the remaining corn lot. Reductions of aflatoxin achieved by conventional heating (using a convection oven and water bath) and microwave heating to degrade the aflatoxin were also investigated. The presence of water is critical to aflatoxin degradation during heating. Aflatoxin is very stable during dry heating and a temperature of 150 ºC is required to initiate decomposition of aflatoxin. HPLC-MS studies revealed that aflatoxin B1 was converted into its enantiomer by dry heating. During wet heating for 1 h at 80°C, 73% of the AFB1 was degraded. Degradation of AFB1 by wet heating involves hydrolysis of the furofuran moiety and the lactone ring along with further decarboxylation. Microwave heating produced the same degradation products as conventional heating, indicating that degradation during microwave heating is purely due to its thermal effects. Degradation of aflatoxin by food additives was also investigated. Four selected food additives, i.e., sodium bisulfite, sodium hypochlorite, citric acid, and ammonium persulfate, were able to effectively (\u3e86%) degrade aflatoxin with no substrate by heating at 90 ºC for 1 h with 1% (by weight) food additive solutions. A protective effect of the substrate was found for aflatoxin degradation in DWG and CDS. Citric acid is the most promising additive for degrading aflatoxin since it has been classified as GRAS (generally recognized as safe) by FDA. Degradation of aflatoxin B1 by citric acid was through acid-catalyzed hydrolysis which converts the AFB1 to AFB2 and AFB 1-Citric (C23 H19 O13). Aflatoxin reduction was enhanced by adding more citric acid and prolonging the heating time. Performance of the HVACP system and generation of reactive species were characterized using optical emission spectroscopy and optical absorption spectroscopy. During the 120 s HVACP treatment, ozone concentrations generated by HVACP follows a logarithmic function for both the gas MA and air (R2 adj \u3e 0.98). Ozone generation rate and final ozone was higher when the MA gas was used instead of air, and when the relative humidity was low (5%). Aflatoxin in corn could be degraded by HVACP treatment within minutes. Three kinetic models (a first-order, a Weibull, and a logistic model) were fitted to the aflatoxin degradation data. The logistic model was found to be the best to describe the degradation kinetics of aflatoxin by HVACP with a high coefficient of determination (R2 ≥ 0.99). Degradation of aflatoxin by HVACP was influenced by the type of materials treated. It was more readily degraded in DWG and DDG than in DDGS and CDS. A Relative Importance Analysis indicated that sample amount, treatment time, and grain depth were critical parameters that determine percent reduction of aflatoxin in DDGS by HVACP Treatment. The mechanism whereby AFB1 is degraded during HVACP treatment involved hydrogenation, hydration, and oxidation of the furan ring. The hydrogen radical, hydroxyl radical, hydroperoxyl radical and ozone were proposed as the major reactive agents for AFB1 degradation generated by HVACP treatment. Based on the literature, the degradation produced changes in the furofuran and lactone rings, and cyclopantenone and methoxyl structures. These should pose less of a risk to biological activity than AFB 1 according to their structure-bioactivity relationship. (Abstract shortened by ProQuest.

Removal of trimethylamine and isovaleric acid from gas streams in a continuous flow surface discharge plasma reactor

International audienceThe removal of isovaleric acid (IVA) and trimethylamine (TMA) using nonthermal plasma (NTP) in a continuous surface discharge reactor is investigated. The influence of the energy density shows that its increment is accompanied by the increase of the removal rate. At flowrate equal to 2 m3 h−1, when energy density extends three times, the removal rates of IVA and TMA are increased from 5 to 15 mmol m−2 h−1 and from 4 to 11 mmol m−2 h−1, respectively. The impact of relative humidity (RH) is also studied. An increase in % RH (up to 20%) leads to a decrease of the removal rate. Additionally, the formation of by-products in the surface discharge reactor and the plausible reaction mechanism of the two VOC were also detected and discussed. Moreover, a kinetic model taking into account the mass transfer step is developed in order to represent the experimental results. The model shows a good agreement with experimental results

Chemical assessment of non-thermal plasma for reduction of odour emissions from pig houses

Methanethiol is an important odorant from pig houses, but it can be difficult to measure due to low concentrations, high volatility and becauseit easily reacts to form dimethyl disulphide. A method was developedfor sampling and measuring methanethiol with minimum artefact formation using sorbent materials and thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). As odour from pig production can be a nuisance to neighbours, a non-thermal plasma system for odour removal was tested on emissions from pig houses. The experiments showed good removal for some odorants, especially indole and 3-methyl-1H-indole, and a high degree of particle removal. Gas/particle partitioning of odorants in a pig house was also investigatedand a method for measuring odorants in particles by filters and TDGC-MS was developed and evaluated. Only low concentrations and low fractions of odorants were found in the particle phase, thus the contribution to odour from particles was evaluated to be limited

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas

Plasma-liquid interactions: a review and roadmap

Plasma-liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas