Seong Bong Kim

We present an experimentally validated, engineering-oriented framework for the design and operation of pin-to-water (PTW) atmospheric discharges to produce hydrogen peroxide (H₂O₂) on demand. Motivated by industrial needs for safe, point-of-use oxidant supply, we combine time-resolved diagnostics (FTIR, OES), liquid-phase analysis (ion chromatography, pH, conductivity), and coupled plasma-chemistry/fluid simulations to link plasma state to aqueous H₂O₂ yield. Under the tested conditions (14.3 kHz, 0.2 kW; electrode to quartz wall distance 12–14 mm; coolant setpoints 0–40 °C), H₂O₂ concentration follows a reproducible non-monotonic trajectory: rapid accumulation during the early treatment (typical peak at ~15–25 min), followed by decline with continued operation. The decline coincides with a robust vibrational-temperature (T_vib) threshold near ~4900 K measured from N₂ emission, and with concurrent NO_X accumulation and bulk acidification. Global chemistry modeling and Fluent flow fields reproduce the observed trend and show that both vibrational excitation (kinetics) and convective transport (mass/heat transfer) determine the productive time window. Based on these results, we formulate practical design rules—electrode gap (power density), discharge current control, thermal/flow management, water quality, and OES-based T_vib monitoring with an automated stop rule—that maximize H₂O₂ yield while avoiding NO_X-dominated suppression. The study provides a clear path for transforming mechanistic plasma insights into deployable, industrial H₂O₂ generator designs.

This study investigated the synergistic effects of microorganism inactivation using underwater plasma, focusing on applications relevant to food safety. The underwater plasma was generated by capillary electrodes in 10% saltwater circulated at 5 t/h. Two representative bacteria, Escherichia coli (Gram-negative) and Microbacterium testaceum (Gram-positive), were selected due to their relevance to food and water contamination. Inactivation kinetics were assessed through first-order rate constants (k) under direct, indirect, and total (combined) treatments. The rate constant (k-value) difference between total and indirect treatment for E. coli reached 0.1015 at 5 min of discharge, while M. testaceum showed a smaller difference of 0.0083 at 20 min. These results suggest that microorganisms pre-damaged by direct plasma exposure become more susceptible to long-lived reactive species like hydrogen peroxide. The findings indicate that underwater plasma holds significant potential as an effective non-thermal disinfection method for brine solutions, fresh produce, and food-contact surfaces.

Recycling waste brine from the Kimchi production process is an important environmental and industry issue. We applied an underwater plasma to reduce food-borne pathogens in the waste brine. The capillary electrodes supplied by alternating current (AC) bi-polar pulsed power were applied to treat 100 L of waste brine. The inactivation efficacy was analyzed using four different agars (Tryptic Soy Agar (TSA), Marine agar (MA), de Man Rogosa Sharpe Agar (MRS), and Yeast Extract–Peptone–Dextrose (YPD), respectively. The microbial population was reduced linearly with treatment time, irrespective of culturing medium. The inactivation followed the log-linear model (R²: 0.96–0.99). The reusability of plasma-treated waste brine (PTWB) was determined by five parameters (salinity, pH, acidity, reducing sugar, and the population of microorganisms) of salted Kimchi cabbage, and they were compared with newly made brine (NMB) and waste brine (WB), respectively. The results showed that the quality of salted Kimchi cabbage prepared by PTWB was not significantly different from that of NMB, indicating that the underwater plasma treatment is feasible to reuse waste brine in the salting process of Kimchi production.

Atmospheric plasmas have been applied for the inactivation of microorganisms. Industrials demand to investigate the relation of the key reactive species induced by plasmas and the operating parameters including boundary conditions in order to control plasma treatment processes. In this study, we investigated the effect of gap distance between a pin-electrode and water surface on inactivation efficacy. When the gap distance decreased from 5 mm to 1 mm, the reduction of Escherichia coli (E. coli) was increased to more than 4 log CFU/mL. The reactive oxygen species measured optically and spectrophotometrically were influenced by gap distance. The results from electron spin resonance (ESR) analysis showed that the pin-to-water plasma generated hydroxyl radical (OH•) and singlet oxygen (¹O₂) in the water and superoxide radical (O₂⁻•) served as a precursor of OH•. The inactivation of E. coli was significantly alleviated by sodium azide (¹O₂ scavenger), indicating that ¹O₂ contributes the most to bacterial inactivation. These findings provide a potentially effective strategy for bacterial inactivation using a pin-to-water plasma.

Atmospheric plasmas have applied for inactivation microorganisms. Industrials demand to investigate the relation of the key reactive species induced by plasmas and the operating parameters including boundary conditions in order to control plasma treatment processes. Plasma activated water or plasma treated water is one of the promising methods for bacterial inactivation due to eco-friendliness and ease of use. We investigated the plasma treated water using a pin-to-water plasma focusing on the gap distance between a pin-electrode and water surface. When the gap distance decreased from 5 mm to 1 mm, concentrations of the reactive species such as hydroxyl radicals (OH•) and singlet oxygens ( 1 O 2 ) related to bacterial inactivation were increased and the reduction of Escherichia coli ( E. coli ) in a planktonic state was more than 4 log CFU/ml in the case of 1mm gap. The results from electron spin resonance (ESR) analysis showed that the pin-to-water plasma generated hydroxyl radical (OH•) and singlet oxygen ( 1 O 2 ) in the water and superoxide radical (O 2 - •) served as a precursor of OH•. The inactivation of E. coli was significantly alleviated by sodium azide ( 1 O 2 scavenger), indicating that 1 O 2 contributes the most to the bacterial inactivation. These findings provide a potentially effective strategy for bacterial inactivation using a pin-to-water plasma.

An effective and eco-friendly technology is needed to prevent postharvest loss of onion bulbs during cold storage. This study investigated the effect of gaseous ozone on the decay and quality of onion bulbs during storage at 2 °C and 70% relative humidity for two months. Gaseous ozone was adjusted to a concentration of 1.27 ± 0.024 ppm in the storage room by generating a high voltage discharge in air. After two months of storage, gaseous ozone significantly reduced the counts of aerobic bacteria (e.g., Rahnella aquatilis) and fungi (e.g., yeast and mold) in the onion bulbs by 4 log (CFU g⁻¹) and 0.92 log (CFU g⁻¹) compared with those of an untreated control, respectively. The microbial reduction by gaseous ozone resulted in a lower rotten rate of the onion bulbs, which was less than 20.0% compared with that of the untreated control. Moreover, the ozone exposure extended the storage life of the onion bulbs by delaying its color change and softening during storage. Our results suggest that gaseous ozone can control the decay of onion bulbs safely during storage.

Low-temperature atmospheric pressure plasma technology has been used in agriculture and plant science by direct and indirect treatment of bio-samples. However, the cellular and molecular mechanisms affected by plasma-activated water (PAW) are largely unexplored. In this study, PAW generated from a surface dielectric barrier discharge (SDBD) device was used for plant development. Physicochemical analysis was performed to confirm the PAW properties that correlated with the plasma treatment time. Arabidopsis thaliana L. was utilized to study the effect of the PAW treatment in the early developmental stage. The plasma-activated water samples are denoted as PAW5 time in minutes (min), PAW7 min, PAW12 min, PAW19 min and PAW40 min with the plasma treatment time. Seedlings grown in the PAW5, PAW7 and PAW12 had increased root lengths while the root lengths were decreased in the PAW19 and PAW40. In the cellular level observation, the PAW treatment specifically increased the root hair numbers per unit of the root but suppressed the root hair length in the PAW, indicating that PAW mainly modulates the root hair cell density in the root. Furthermore, we found that the root hair density and length at PAW5 in maximal observed conditions were positively regulated by root developmental-related genes including COBRA-LIKE9 (COBL9), XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE9 (XTH9), XTH17, AUXIN1 (AUX1) and LIKE-AUXIN (LAX3).

Ginseng (Panax ginseng Meyer) sprouts are grown to whole plants in 20 to 25 days in a soil-less cultivation system and then used as a medicinal vegetable. As a nitrogen (N) source, plasma-treated water (PTW) has been used to enhance the seed germination and seedling growth of many crops but has not been investigated for its effects on ginseng sprouts. This study established an in-situ system for N-containing water production using plasma technology and evaluated the effects of the PTW on ginseng growth and its bioactive phytochemicals compared with those of an untreated control. The PTW became weakly acidic 30 min after the air discharge at the electrodes because of the formation of nitrate (NO₃^‒) and nitrite (NO₂^‒) in the water. The NO₃^‒ and NO₂^‒ in the PTW, together with potassium ions (K⁺), enhanced the shoot biomass of the ginseng sprout by 26.5% compared to the untreated control. The ginseng sprout grown in the PTW had accumulated more free amino acids and ginsenosides in the sprout at 25 days after planting. Therefore, PTW can be used as a liquid N fertilizer for P. ginseng growth and phytochemical accumulation during sprouting under aeroponic conditions.

The dependence of the plasma discharge performance on the size of the honeycomb monolith in a sandwich-type honeycomb monolith plasma reactor operated under humidified air conditions was investigated. In addition, the effect of the feed gas temperature on the plasma discharge was also examined in the low-temperature range (25 °C–42 °C), which is similar to the typical temperature of the actual surrounding ambient air. The results showed that variation of the temperature significantly affects the discharge power, i.e., the discharge power decreases with increasing temperature. The results also indicated that, in the absence of the honeycomb monolith in the reactor, the plasma discharge did not occur inside the discharge zone created by two parallel perforated disks. However, when the honeycomb monolith was sandwiched between the two electrodes, the discharge developed between them because of the generated surface discharge spread through the honeycomb channels. Interestingly, a parallel relationship exists between monoliths with two different diameters in terms of their energy density and energy efficiency for O ₃ generation. These results suggest that the use of a monolith with a small diameter, instead of the original large commercial monolith, is sufficient when conducting research on the honeycomb discharge, as it facilitates experimental design.