Gas Phase Surface Discharge Plasma Research Articles

Modeling the effect of initial cell concentration and soluble solids on the plasma inactivation of yeast in apple juices

Atmospheric cold plasma is a powerful and profitable microbial decontamination technology in the food industry. The microbial load and food matrix have a great influence on the plasma inactivation effect. This study aimed to quantify the effects of initial cell concentration and soluble solids on the inactivation of yeast in apple juice by gas-phase surface discharge plasma. A computer simulation model was developed to predict the inactivation process using commercial finite element software, COMSOL Multiphysics, and the model was verified by experiments. Studies have shown that the inactivation of yeast was affected by the initial cell concentration and soluble solids. These effects were quantified by fitting equations and used as model inputs. The simulation model predicted the D-value of plasma inactivation of yeast under different discharge voltages and apple juice volume, which was verified in experiments. Therefore, the established model can be used for plasma development to predict how the food matrix affects the inactivation process, thereby providing useful and practical tools for amplifying the commercial application of plasma.

Emerging Technologies for Degradation of Dichlorvos: A Review

Dichlorvos (O,O-dimethyl O-(2,2-dichlorovinyl)phosphate, DDVP) is a widely acknowledged broad-spectrum organophosphorus insecticide and acaracide. This pesticide has been used for more than four decades and is still in strong demand in many developing countries. Extensive application of DDVP in agriculture has caused severe hazardous impacts on living systems. The International Agency for Research on Cancer of the World Health Organization considered DDVP among the list of 2B carcinogens, which means a certain extent of cancer risk. Hence, removing DDVP from the environment has attracted worldwide attention. Many studies have tested the removal of DDVP using different kinds of physicochemical methods including gas phase surface discharge plasma, physical adsorption, hydrodynamic cavitation, and nanoparticles. Compared to physicochemical methods, microbial degradation is regarded as an environmentally friendly approach to solve several environmental issues caused by pesticides. Till now, several DDVP-degrading microbes have been isolated and reported, including but not limited to Cunninghamella, Fusarium, Talaromyces, Aspergillus, Penicillium, Ochrobium, Pseudomonas, Bacillus, and Trichoderma. Moreover, the possible degradation pathways of DDVP and the transformation of several metabolites have been fully explored. In addition, there are a few studies on DDVP-degrading enzymes and the corresponding genes in microorganisms. However, further research relevant to molecular biology and genetics are still needed to explore the bioremediation of DDVP. This review summarizes the latest development in DDVP degradation and provides reasonable and scientific advice for pesticide removal in contaminated environments.

Degradation of pharmaceutical contaminants by bubbling gas phase surface discharge plasma combined with g-C3N4 photocatalysis

The feasibility of using gas phase surface discharge with microporous bubbling combined with g-C3N4 photocatalysis for the degradation of pharmaceutical contaminants was evaluated.

Gas phase surface discharge plasma model for yeast inactivation in water

Cold atmospheric plasma is a promising sterilization technology in the food industry. However, there are only a few studies on the process of inactivating microorganisms in liquids, and it is necessary to establish an efficient prediction model before widespread industrial application. In this study, the commercial software COMSOL was used to establish a gas phase surface discharge plasma reactor simulation model, and experiments were subsequently performed to validate the model. Results showed that increasing the initial concentration of yeast in water has a negative effect on the inactivation process. In contrast, yeast inactivation was not significantly affected by reactor diameter changes from 40 mm to 50 mm. The model showed good fit to the experimental data under various operating conditions, and the value of the parameter associated with the reaction coefficients provided insight into the process. This model can be used for process design and improvement of plasma-inactivated liquid foods.

Surface plasma discharges for the preservation of fresh-cut apples: microbial inactivation and quality attributes

Sustainable and cost effective food preservation techniques are of industrial, environmental and public health significance globally. A promising means for the gentle but efficient sanitation of foods is the application of cold atmospheric plasma. Here, the preservation of fresh-cut apples was investigated using a gas phase surface discharge plasma (SDP) reactor within an exposure chamber. Results show that the microbial load reduction of the fresh-cut apples was found to be strongly dependent on the storage time and preservation method, e.g. refrigeration (control), SDP-room temperature and SDP-refrigeration (SDP-RF). After 6 d of storage, the microbe load on the apple pieces for the SDF-RF treated groups was found to be significantly lower compared to the refrigeration-stored (4 °C) and the SDP only-processed groups, with the lowest bacterial load on the 120 s SDP-RF stored apple pieces (1.76 CFU g−1). Furthermore, the effects of the preservation method on the quality attributes (weight loss, firmness, and physical appearance), and the surface chemistry directly after cutting and SDP processing, as well as the activities of polyphenol oxidase and peroxidase after the different duration of storage were evaluated. This study successfully demonstrates the feasibility of SDP for the effective preservation of fresh-cut apples and contributes to the fundamental understanding of surface plasma-induced effects on the microbial inactivation and postharvest quality of fresh-cut fruits.

Application of gas phase surface discharge plasma with a spray reactor for Zygosaccharomyces rouxii LB inactivation in apple juice

Abstract The effects of the gas phase surface discharge plasma system with a spray reactor on yeast in 12, 36, and 60°Brix apple juice were evaluated. Results indicated that the number of Zygosaccharomyces rouxii LB cells in 0.5 L of 12°Brix apple juice was reduced by 5.60 log10 after discharge plasma treatment for 30 min. When the soluble solids content increased from 12 to 60°Brix, yeast inactivation was decreased by 2.55 log10. After treatment, the pH level of the apple juice only slightly increased, and the titratable acidity and concentration of reducing sugars remained unchanged. The total color differences between the plasma-treated and untreated samples in 12, 36, and 60°Brix apple juice were 9.53, 7.97, and 3.86. Meanwhile, the concentrations of alcohols, esters, aldehydes, and ketones—the main components of volatile compounds showed no significant change (p Industrial relevance Inactivation of microorganisms using nonthermal plasma technology can reduce food costs and minimize changes in food products and is therefore an alternative to heat-based technology. The proposed research showed that the gas phase surface discharge plasma treatment with a spray reactor can effectively reduce Zygosaccharomyces rouxii in apple juice. In addition, the effect of plasma treatment on the color and volatile compounds of the apple juice were determined. This study provided a technical support for the application of plasma technology in apple juice processing.

Bactericidal effect of cold plasma on microbiota of commercial fish balls

Abstract This study evaluated the bactericidal effect of cold plasma on three spoilage bacteria isolated from commercial fish balls: Psychrobacter glacincola 38–1, Brochothrix thermosphacta 38–2, and Pseudomonas fragi 38–8. Bacterial suspensions were treated by pulsed discharge plasma (PDP, 50 Hz, 3.0 L/min) and gas phase surface discharge plasma (GPSDP, 75 Hz, 6.5 L/min). The inactivation behavior was closely related to the peak discharge voltage, initial bacterial concentration, and exposure time. After treatment with GPSDP for 300 s (12.8 kV), a reduction of 6.87, 4.81 and 3.32 log10 CFU/mL was observed for 38–1, 38–2 and 38–8, respectively. However, when the voltage of PDP reached 20 kV, inactivation was initiated. P. glacincola 38–1 was the most sensitive to plasma treatment. After 4-min treatment with PDP or 30-s treatment with GPSDP, the 38–1 (approximately 105 CFU/mL) were completely inactivated. A Weibull model and a modified Whiting-Buchanan model provided a good fit for the survival curves, with R2 ≥ 96%. After plasma treatment, deformation and rupture of bacterial cells were observed by SEM and TEM; the leakage of cellular contents was also observed by TEM. The oxidation by active particles (H2O2 and O3) was the primary mechanism of bacterial inactivation exerted by GPSDP. PDP acted synergistically through physical penetration and chemical oxidation, which combined to lead to cell death. Industrial relevance Commercial fish balls are popular in China, and they are usually transported and stored in the cold chain (mainly frozen environment). Although efficient cold chain can reduce the rate of microbial changes in fish balls, there are still limits of cold chain. The inevitable fluctuations in temperature during cold chain provide conditions for the attachment and growth of cold-tolerant bacteria that may lead to spoilage of commercial fish ball. The proposed research gives insight into how to control microbial contamination of commercial fish balls. Cold plasma treatment proved to be effective at killing the three bacteria tested, and the inactivation achieved by GPSDP was far superior to that achieved by PDP treatment. Dynamic fitting of a mathematical model was performed to describe the inactivation behaviors. This also provides a basis for predicting the inactivation of microorganisms. The study offers firm theoretical foundation and practical guidance for the application of cold plasma in the quality control of commercial fish balls, and further contributes to the safety of foods in cold chain.

Removal of organophosphorus pesticide residues from Lycium barbarum by gas phase surface discharge plasma

Pesticides are widely used in commercial goji Lycium barbarum cultivation to prevent damage of the delicate fruits by insects, potentially leading to insecticide and fungicide residues at levels dangerous to human health. In this study, removal of organophosphorus pesticide (OP) residues (i.e. omethoate and dichlorvos) from the surface of L. barbarum was conducted using a gas phase surface discharge (GPSD) plasma system. ICCD and GC–MS measurements showed that a homogeneous and uniform GPSD glow-like plasma could be achieved and the efficiency of OP residues degradation greatly depended on the applied voltage and plasma exposure time, with 99.55% and 96.83% efficiency recorded for omethoate and dichlorvos (DDVP), respectively after 30 min GPSD plasma exposure at the discharge voltage of 10 kV. FT-IR and chemical analysis of the intermediates produced during GPSD exposure revealed that the omethoate and DDVP molecules could be completely degraded into nontoxic species, at the appropriate dosage of GPSD plasma exposure, without compromising the quality of L. barbarum. Based on the experimental and simulation results, a mechanism of OP degradation attributed to energetic electrons and highly reactive species generated by GPSD plasma was proposed.

Persulfate activation in gas phase surface discharge plasma for synergetic removal of antibiotic in water

A process of persulfate (PS) activation in gas phase surface discharge plasma was studied to facilitate the removal of tetracycline (TC) in water. PS was introduced into the discharge reactor, and the effects of PS added dosage and applied voltage on TC removal were determined. The results showed that PS addition exhibited significant synergistic effect, promoting the degradation efficiency and removal rate of TC. Increasing the applied voltage was beneficial to the enhancement of TC decomposition. The removal efficiency and first order kinetic constant were achieved 87.5% and 0.232 min−1 at a PS addition dosage of 20:1 (molar ratio of PS to TC) and a discharge voltage of 7 kV after 15 min treatment, respectively. Especially the calculated synergistic factor achieved 1.856, indicating the synergistic effect was existed. Besides, the removal of the synergistic system was influenced remarkably by the other operation parameters, including air flow rate, initial TC concentration, and initial pH value. The mineralization of TC and intermediates produced during the synergistic process was explored by UV–vis spectrogram and TOC analyses. The synergistic effect could be explained by the enhanced formation of hydroxyl and sulfate radicals that were generated from the activation of PS in discharge plasma. The evolution of the main degradation byproducts in the synergism process was investigated by HPLC–MS.

Humic acid removal from micro-polluted source water in the presence of inorganic salts in a gas-phase surface discharge plasma system

Abstract Humic acid (HA), a predominant type of natural organic matter in surface water, had several potential environmental and health risks. A gas phase surface discharge plasma system was employed to eliminate HA from micro-polluted surface water, and the effects of some concomitant inorganic ions on HA removal were evaluated. The experimental results showed that approximately 89.4% of HA could be smoothly eliminated after 40 min of the discharge plasma treatment, and the HA removal process could be fitted well by the first-order kinetic model. The presence of anions such as CO32− and Cl− in the natural water were adverse for the HA removal due to their competition for the active species, whereas the effects of NO3− and SO42− on the HA removal could be neglected; this deduction was also confirmed via the evolution of fluorescence spectra intensity of OH radicals. Although Cu2+ could react with H2O2 via Fenton-like reaction, its presence was still adverse for the HA removal due to the complexing effect of Cu2+ with HA molecules. In addition, the HA removal processes were characterized by UV–Vis spectrum, DOC removal, specific absorbance parameters, and three-dimensional fluorescence spectrum analysis.

Humic acid removal from micro-polluted source water using gas phase surface discharge plasma at different grounding modes

Humic acid (HA) was a predominant natural organic matter in ground water and surface waters. The removal of HA from micro-polluted source water using a gas phase surface discharge plasma at different grounding modes was studied, and three kinds of grounding modes (iron wire mesh, aluminized paper, and water) were selected. The experimental results illustrated that approximately 95.3% of HA in water was removed within 30 min’s discharge plasma treatment in the iron wire mesh electrode system, and it was 89.5% and 84.6% in the aluminized paper electrode system and water electrode system, respectively; although the strongest streamer discharge and the highest ozone equivalent concentration were both observed in the iron wire mesh electrode system. The discharge plasma treatment resulted in a relatively more homogeneous surface topography in the HA molecules as analyzed by scanning electron microscope (SEM), especially in the iron wire mesh electrode system and in the aluminized paper electrode system. The decomposition process of HA at different grounding modes was analyzed and compared via the evolution of the UV–Vis spectrum, dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA) and UV absorption ratios with treatment time. In addition, the HA removal efficacy in this study was comparable with those of some other techniques.

Evaluation of the potentials of humic acid removal in water by gas phase surface discharge plasma

Degradation of humic acid (HA), a predominant type of natural organic matter in ground water and surface waters, was conducted using a gas phase surface discharge plasma system. HA standard and two surface waters (Wetland, and Weihe River) were selected as the targets. The experimental results showed that about 90.9% of standard HA was smoothly removed within 40 min's discharge plasma treatment at discharge voltage 23.0 kV, and the removal process fitted the first-order kinetic model. Roles of some active species in HA removal were studied by evaluating the effects of solution pH and OH radical scavenger; and the results presented that O3 and OH radical played significant roles in HA removal. Scanning electron microscope (SEM) and FTIR analysis showed that HA surface topography and molecular structure were changed during discharge plasma process. The mineralization of HA was analyzed by UV–Vis spectrum, dissolved organic carbon (DOC), specific UV absorbance (SUVA), UV absorption ratios, and excitation-emission matrix (EEM) fluorescence. The formation of disinfection by-products during HA sample chlorination was also identified, and CHCl3 was detected as the main disinfection by-product, but discharge plasma treatment could suppress its formation to a certain extent. In addition, approximately 82.3% and 67.9% of UV254 were removed for the Weihe River water and the Wetland water after 40 min of discharge plasma treatment.

Organic acids enhanced decoloration of azo dye in gas phase surface discharge plasma system

A gas phase surface discharge plasma combined with organic acids system was developed to enhance active species mass transfer and dye-containing wastewater treatment efficacy, with Acid Orange II (AO7) as the model pollutant. The effects of discharge voltage and various organic acid additives (acetic acid, lactic acid and nonoic acid) on AO7 decoloration efficiency were evaluated. The experimental results showed that an AO7 decoloration efficiency of approximately 69.0% was obtained within 4min of discharge plasma treatment without organic acid addition, which was improved to 82.8%, 83.5% and 88.6% within the same treatment time with the addition of acetic acid, lactic acid and nonoic acid, respectively. The enhancement effects on AO7 decoloration efficiency could be attributed to the decrease in aqueous surface tension, improvement in bubble distribution and shape, and increase in ozone equivalent concentration. The AO7 wastewater was biodegradable after discharge plasma treatment with the addition of organic acid. AO7 decomposition intermediates were analyzed by UV–vis spectrometry and GC–MS; 2-naphthol, 1,4-benzoquinone, phthalic anhydride, coumarin, 1,2-naphthoquinone, and 2-formyl-benzoic acid were detected. A possible pathway for AO7 decomposition in this system was proposed.

Removal of Elemental Mercury by Gas Phase Surface Discharge Plasma

The removal of elemental mercury (Hg0) with the reactive species produced by gas phase surface discharge plasma was studied. The effects of several operational parameters, such as applied voltage, inlet Hg0 concentration and gas humidity, were investigated. The removal of Hg0 was significantly promoted by an increase in the applied voltage of the reactor system. Hg0 oxidation efficiency decreases with increasing inlet Hg0 concentration. Furthermore, with the addition of H2O, Hg0 oxidation is remarkably restrained.