Non-thermal Atmospheric Pressure Plasma Research Articles

Effect of LF-microwave hybrid plasma treatment on radish seed germination and sprout growth

The atmospheric pressure non-thermal plasma generated by low-frequency (LF)-microwave hybrid discharge has been employed to investigate the effects of plasma treatment on the germination and growth of radish (Raphanus sativus L.) sprout seeds. The plasma generated with admixture discharge gas of Ar-O2 was adopted for the irradiation of seeds. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses were performed to elucidate the physical and chemical state changes of seed surfaces after plasma treatment. The reactive species produced in the plasma were investigated using optical emission spectroscopy (OES) and chemical indicator (CI). The results demonstrate that higher reactive oxygen species were generated from the LF-microwave hybrid plasma compared to conventional LF plasma jet. Moreover, the higher germination percentage and shorter germination time were obtained with the LF-microwave hybrid plasma compared to LF plasma jet and control group. It is considered that reactive species produced in the LF-microwave hybrid plasma are related to the germination time of the radish sprout seed.

Wound Healing After Biopsy in the Mobile Oral Mucosa Using a Nonthermal Atmospheric Pressure Plasma

A biopsy is performed for diagnostic purposes and provides valuable information through a histopathological study. It is possible to use a suture or some other surgical closure method for wound closure. This study determined wound healing time in an excisional biopsy in the mobile oral mucosa after using nonthermal atmospheric pressure plasma (NTAPP). The NTAPP has applied after the biopsy in two treatments for 3 min each and 1 h apart. The repair time was between one and seven days, with an average of three days, considering as a reference of the repair time that the oral mucosa in the biopsy area took its color, consistency, and surface. None of the patients undergoing treatment with NTAPP showed adverse effects after a minimum of six months of clinical follow up. The patients treated with NTAPP showed a significant reduction in the tissue repair time, without infection and the absence of postoperative pain, presenting an almost immediate recovery of oral functions; the patients did not require analgesics. The application of NTAPP to wounds after taking a biopsy of the mobile oral mucosa could be recommended as a safe and reliable alternative to repair tissue in this type of wound.

Surface Characterization, Antimicrobial Activity of Nonthermal Atmospheric-Pressure Plasma Jet on Polyvinyl Siloxane Impression Materials.

Background and Objectives The antimicrobial efficacy of a nonthermal atmospheric-pressure plasma jet (NAPPJ) on dental impression materials was investigated. Materials and Methods Type 3 polyvinyl siloxane was used as the impression material, and air and nitrogen NAPPJ were applied. The antibacterial effect of the NAPPJ was measured using the number of colony-forming units (CFUs) and scanning electron microscopy (SEM) images of Streptococcus mutans. Surface chemical characteristics of the impression material were examined using X-ray photoelectron spectroscopy (XPS) and contact angle measurement. Additionally, physical properties were analyzed through surface roughness measurement, detail reproduction, and strain-in-compression test. Results Compared with the control group, the plasma treatment group showed ruptured bacteria membranes, destroyed bacteria structures, a significant reduction in the number of CFUs, and a significantly reduced contact angle. Further, XPS analysis showed that their surface was significantly richer in hydroxyl groups. The surface roughness, detail reproduction, and strain-in-compression results indicated no significant differences between the plasma treatment and control groups. NAPPJ treatment could remove bacteria from polyvinyl siloxane dental impression materials without changing the surface's physical properties. Conclusion Therefore, it is considered a promising method for disinfection.

Wound healing in db/db mice with type 2 diabetes using non-contact exposure with an argon non-thermal atmospheric pressure plasma jet device.

A non-thermal atmospheric pressure plasma jet (APPJ) may stimulate cells and tissues or result in cell death depending on the intensity of plasma at the target; therefore, we herein investigated the effects of non-thermal plasma under non-contact conditions on the healing of full-thickness wounds in diabetic mice (DM+ group) and normal mice (DM- group). A hydrogen peroxide colorimetric method and high performance liquid chromatography showed that APPJ produced low amounts of reactive oxygen and nitrogen species. Ten-week-old male C57BL/6j mice with normal blood glucose levels (DM- group) and 10-week-old male C57BLKS/J Iar-+Leprdb/+Leprdb mice (DM+ group) received two full-thickness cutaneous wounds (4 mm in diameter) on both sides of the dorsum. Wounds were treated with or without the plasma jet or argon gas for 1 minute and were then covered with a hydrocolloid dressing (Hydrocolloid), according to which mice were divided into the following groups: DM+Plasma, DM+Argon, DM+Hydrocolloid, DM-Plasma, DM-Argon, and DM-Hydrocolloid. Exudate weights, wound areas, and wound area ratios were recorded every day. Hematoxylin and eosin staining was performed to assess re-epithelialization and α-SMA immunohistological staining to evaluate the formation of new blood vessels. Non-thermal plasma under non-contact conditions reduced the production of exudate. Exudate weights were smaller in the DM+Plasma group than in the DM+Hydrocolloid and DM+Argon groups. The wound area ratio was smaller for plasma-treated wounds, and was also smaller in the DM+Plasma group than in the DM+Hydrocolloid and DM+Argon groups on days 1–21 (p<0.01). Wound areas were smaller in the DM-Plasma group than in the DM-Argon group until day 14 and differences were significant on days 1–5 (p<0.01). The percentage of re-epithelialization was significantly higher in the DM+Plasma group than in the DM+Argon and DM+Hydrocolloid groups (p<0.01). The number of new blood vessels that had formed by day 7 was significantly higher in the DM+Plasma group than in the DM+Hydrocolloid and DM+Argon groups (p<0.05). These results indicate that treatment with the current non-thermal plasma APPJ device under non-contact conditions accelerated wound healing in diabetic mice.

Characterization and evaluation of cold atmospheric plasma as seedborne fungal disinfectant and promoting mediator for physico-chemical characteristics of Moringa oleifera seedlings

Non-thermal atmospheric pressure plasmas are a powerful tool to impact seed germination and microbial decontamination. Air large volume atmospheric pressure glow discharge plasma was developed and investigated to improve the biological activities of Moringa oleifera seeds. Ninty ns magnetic pulse compression high voltage system was used to generate the plasma. The plasma discharges current increases with increasing applied voltage and it decreases with increasing discharge gap. There was a steady reduction in the count of seedborne fungi on the application of air cold plasma with complete elimination of fungi at ≥ 10.94 mJ per pulse. The low doses of plasma (2.46 and 4.35 mJ) induced an increase in the seed germination, a significant increase in chlorophyll content (chl a and chl b) and antioxidant activities of the seedlings emerged from soaked or wet seeds rather than dry seeds. At lower plasma doses (2.46 and 4.35 mJ) there was a significant increase in leaf area and chlorophyll content (chl a and chl b) of the seedlings that emerged from H2O2 soaked seeds rather than that of free from H2O2. The plasma was harmful when applied at higher doses (≥ 10.94 mJ) and more harmful to the wet seeds compared to the dry ones.

Oxidative modification in nuclear and mitochondrial DNA and its removal in A549 human lung cancer cells exposed to cold atmospheric-pressure plasma

Non-thermal atmospheric-pressure plasma has emerged as a useful tool in life science research and medicine. Plasma irradiation generates reactive oxygen and nitrogen species (RONS) that stimulate various cellular responses. In this study, we investigated oxidative damage to nuclear and mitochondrial DNA in A549 human lung cancer cells exposed to a helium atmospheric-pressure plasma jet (APPJ). APPJ irradiation decreased the viability of A549 cells and increased intracellular RONS levels. The formation of 8-oxoguanine (8-oxoG), a representative oxidized form of a DNA base, was observed in nuclear DNA. Pretreatment of A549 cells with an antioxidant reagent prior to APPJ irradiation suppressed the increase in 8-oxoG level. The 8-oxoG level gradually decreased during cell culture, suggesting that 8-oxoG was removed from nuclear DNA after APPJ irradiation. Formation of 8-oxoG was also observed in mitochondrial DNA, indicating the accumulation of RONS in mitochondria.

Research progress in the application of non-thermal atmospheric pressure plasma in dentin bonding

As a convenient and effective surface modification approach, non-thermal atmospheric pressure plasma (NTAPP)can be used to improve dentin bonding, and has recently become a research focus. Studies have shown that NTAPP can alter dentin surface properties, improve the penetration and polymerization of adhesives, stimulate the cross-linking of collagen, and change the micro-morphology and element content of dentin surface, thus improve the dentin bonding quality. This article introduces the current research progress in the application of NTAPP in the field of dentin bonding, in order to provide innovative information for future research in optimization of the quality of dentin bonding.

&lt;i&gt;In vitro&lt;/i&gt; study on non-thermal argon plasma in improving the bonding efficacy between dentin and self-etch adhesive systems

Self-etch adhesive systems have the advantages of simple operating steps and low technique sensitivity. However, some deficiencies of self-etch adhesive result that the immediate bonding strength between self-etch adhesive and dentine is not so high. Non-thermal atmospheric pressure plasma (NTAPP) can be used for surface modification. Previous studies of our research group have proven that NTAPP can improve bonding durability between dentine and etch-and-rinse adhesive. However, it is still unknown whether NTAPP can improve bonding strength between dentine and self-etch adhesive. The study observed the contact angle on dentine surface, the adhesive permeability and MTBS. The study proved that NTAPP can improve dentine surface wettability, clear up smear layer, and enhanced the self-etch adhesive permeability in dentine bonding interface. In conclusion, NTAPP could improve the bonding strength between dentine and self-etch adhesive systems. The most optimum treating time was 15 s.

Experimental and numerical study on diazinon removal using plasma bubble column reactor: Modeling, kinetics, mechanisms, and degradation products

Diazinone is the most commonly used pesticide worldwide. In this study, experimental and numerical analyses were employed to model and optimize the degradation and mineralization of diazinon using remotely generated non-thermal atmospheric pressure plasma. The initial concentration of diazinon, pH of the medium, and flow rate of the plasma feeding gas were considered as the salient factors in the modeling and optimization processes. To our knowledge, this study is the first report on the effects of gas composition and flow rate on the type and concentration of remotely generated reactive nitrogen and oxygen species (RNOS). An air gas composition was adopted as the feeding gas for a custom-made dielectric barrier discharge (DBD) plasma generator. Remotely generated gas plasma was introduced into the reactor through a diffuser located at the bottom of the column reactor, and the degradation of diazinon and its derived products was monitored using GC-MS. The decrease in the total organic carbon (TOC) content of the samples due to plasma treatment was traced using a TOC analyzer. Although 83.11% degradation was observed, the maximum TOC removal using this method was only 39.22%. Subsequently, response surface methodology (RSM) was employed to mathematically model the process and observe the correlations between different parameters. Our results suggested a quadratic model for the degradation and TOC removal of the given treatment methods, which further indicated that the initial concentration of the analyte and pH influenced the degradation efficiency. However, the gas flow rate was identified as an important factor in TOC removal. The energy yield of the treatment procedure was 46.2 (gTOCkW−1h−1), suggesting the potential of DBD plasma for the treatment of diazinon-polluted water.

Direct-Contact and Contact-free Treatment of a DBD-like Non-thermal Atmospheric Pressure Plasma Jet on Pseudomonas aeruginosa

In this study, a Dielectric Barrier Discharge (DBD)-like non-thermal atmospheric pressure plasma jet (NTAPPJ) was exposed to the Pseudomonas aeruginosa planktonic bacteria. The P. aeruginosa bacteria were treated by the NTAPPJs in both Ar and He at the non-contact distance (contact-free) and the contact distance (direct-contact). The contact of the NTAPPJs with the bacteria has generated spark discharges in both filamentary mode and diffuse mode. The antibacterial efficacy of the Ar and He NTAPPJs for various treatment times (60, 120, 180, and 300 sec) were investigated by treatment on the bacteria without contact and with contact in both filamentary mode and diffuse mode. The NTAPPJs in both Ar and He caused erosion on the agar surface when treated in direct-contact with the bacteria in the filamentary mode, while the NTAPPJs in Ar in the diffuse mode produced the greatest antibacterial efficacy without damage.

Systematic 1D electric field induced second harmonic measurement on primary-to-secondary transition phase of positive streamer discharge in atmospheric-pressure air

The electric field induced second harmonic generation (E-FISH) technique has been widely utilized for the electric field measurement of atmospheric-pressure nonthermal plasmas. However, the measurement accuracy has not been quantified. Further, the E-FISH signal generation that is necessary to the evaluation of the measurement accuracy has been formulated only for the probe laser beam focused by a spherical lens and not for the cylindrical lens. Here, the E-FISH method utilizing the focusing cylindrical lens was studied for accurate one-dimensional (1D) electric field measurement of the primary-to-secondary transition phase of a single-filament positive streamer discharge generated in atmospheric-pressure air. A combination of numerical analysis and the E-FISH signal measurement was used to establish the radial distribution of the electric field vectors and the accompanying measurement accuracy. The E-FISH methodology captured a distinct evolution in the 1D electric field varying over timescales of ns and length scales of 100 µm. At the instant when the primary streamer arrived at the cathode, the electric field at 3 mm above the cathode surface was found to be as high as 225 Td, while the field at 10 mm above the cathode surface was as low as 5 Td. At the final stage of the primary-to-secondary transition phase completed in 3 ns from the primary streamer arrival at the cathode, the electric field at 3 mm above the cathode was found to be lower than that observed at 10 mm from the cathode; this finding is consistent with predictions made based on a previous model describing the initiation of the secondary streamer discharge and previously published electron density measurement.

Biophysical evaluation of treating adipose tissue-derived stem cells using non-thermal atmospheric pressure plasma

Non-thermal atmospheric pressure plasma (NTAPP) is a partially ionized gas containing fast electrons and relatively slow ions. This study aims to investigate the influences of NTAPP on human adipose tissue-derived stem cells (ADSCs) and examine the feasibility of using optical spectroscopy as a non-destructive method for cell analysis. A plasma jet is used as the source of low-temperature plasma in which pure helium gas is ionized by a high voltage (8 kV) and frequency (6 kHz). ADSCs were exposed to the NTAPP for 30 s, 60 s, 90 s, and 120 s. The efficiency of the plasma treatment was investigated using flow cytometry and optical spectroscopy methods. This study compared surface markers of NTAPP treated and untreated ADSCs using CD90 and CD105 as positive markers. The result proved that NTAPP-exposed ADSCs maintain their stemming. Measuring ADSCS apoptosis by labeling Annexin V-Propidium Iodide showed that the plasma at short exposure time is relatively non-toxic. However, a longer exposure time can lead to apoptosis and necrosis. Moreover, Cell cycle analysis revealed that NTAPP accelerates the cell cycle in very low doses and can cause proliferation. In this experiment, flow cytometry measurements have been used to determine oxidative stress. The results showed that with increasing plasma dose, intracellular ROS levels reduced. This data also suggests that intracellular ROS are not responsible for the cells' viability. Furthermore, we used reflectance spectroscopy as a non-destructive method for evaluating treatment response and comparing this method with cell analysis techniques. The results indicate spectroscopy's efficiency as a method of cell analysis. This study suggests that NTAPP would be an efficient tool to improve ADSCs culture's efficiency in vitro; thus, we support the potential applications of NTAPP in the field of stem cell therapy and regenerative medicine.

Effect of plasma-activated water on microbial quality and physicochemical properties of fresh beef

Abstract This work studies the influence of plasma-activated water (PAW) on the decontamination of beef and its influence on the color, pH, the thiobarbituric acid reactive substance values (TBARS), and total volatile basic nitrogen (TVBN) values of meat. PAW was generated using non-thermal atmospheric pressure plasma jet (NTAPPJ). He + 0.2% N2 and He + 0.2% O2 were used as worker gas to generate PAW. The PAW produced by the He + O2 plasma system exhibited a higher potential for decontamination of beef than that produced by the He + N2 plasma system. The lightness value (L*) of treated beef does not exhibit a noticeable difference with the control one. TBARS values of all treated beef were lower than the rancidity threshold but significantly greater than that of control samples. The TVBN value of control beef samples reached the decay threshold after 18 days of stockpiling, but treated beef remained good. This work reveals that PAW can potentially inhibit the growth of microorganisms in beef.

An Ionization-Driven Air Plasma Jet

Non-thermal atmospheric pressure plasma jets (NAPPJs) using ambient air as the inducer are of particular and desirable interest but with significant challenges. In this study, we report an air APPJ driven by ionization in the afterglow region, resembling noble gas APPJs. A pin-to-nozzle electrode is used for the air plasma jet with a nanosecond-pulsed DC high voltage as the power supply. Results show that the nozzle diameter plays an essential role in forming the air plasma jet. When the nozzle diameter is 3 mm, the air APPJ is driven by ionization in the afterglow region which is proved by the following three phenomena. First, with an exposure time of 0.1 s, an obvious shiny line (the narrow channel plasma) formed by electron accumulation is observed in the jet. The narrow channel becomes much brighter with a grounding pin approaching the nozzle vertically. In comparison, there is no such phenomenon with a 1-mm diameter nozzle. Second, the afterglow region discharge current of the ionization-driven processes is hundreds of mA distinguished from airflow-driven processes, the afterglow region current of which is typically zero. By using E-FISH to measure the electric field in the afterglow region, it can detect the electric field which has a maximum value of 10.5 kV/cm. Third, the intensity of the N2+ band is much stronger with a 3-mm diameter nozzle than with a 1-mm diameter nozzle, indicating that the local electric field plays an important role in the discharge. We expect this study can offer useful guidelines on the design and understanding of ionization-driven air plasma jets.

Plasma Promotes Fungal Cellulase Production by Regulating the Levels of Intracellular NO and Ca2.

For the industrial-scale production of useful enzymes by microorganisms, technological development is required for overcoming a technical bottleneck represented by poor efficiency in the induction of enzyme gene expression and secretion. In this study, we evaluated the potential of a non-thermal atmospheric pressure plasma jet to improve the production efficiency of cellulolytic enzymes in Neurospora crassa, a filamentous fungus. The total activity of cellulolytic enzymes and protein concentration were significantly increased (1.1~1.2 times) in media containing Avicel 24–72 h after 2 and 5 min of plasma treatment. The mRNA levels of four cellulolytic enzymes in fungal hyphae grown in media with Avicel were significantly increased (1.3~17 times) 2–4 h after a 5 min of plasma treatment. The levels of intracellular NO and Ca2+ were increased in plasma-treated fungal hyphae grown in Avicel media after 48 h, and the removal of intracellular NO decreased the activity of cellulolytic enzymes in media and the level of vesicles in fungal hyphae. Our data suggest that plasma treatment can promote the transcription and secretion of cellulolytic enzymes into the culture media in the presence of Avicel (induction condition) by enhancing the intracellular level of NO and Ca2+.

Synergistic antimicrobial effects of atmospheric pressure non-thermal argon plasma and ciprofloxacin antibiotic against multi-drug resistant P. aeruginosa biofilm

Bacterial biofilm formation is regarded as the major cause of infection development, therapeutic failure, and antibiotic resistance. This study aimed to assess the synergistic antibiofilm potential of an atmospheric-pressure non-thermal argon plasma and ciprofloxacin (Cip) against multi-drug-resistant Pseudomonas aeruginosa. Bacterial biofilms were pre-treated with the non-thermal Ar-plasma and subsequently treated with Cip antibiotic. Then, the bacterial biofilm formation level and cell viability were investigated using crystal violet staining, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide, SEM, and fluorescence microscopy, respectively. It was found that a short-time (a few seconds) pretreating with Ar-plasma not only reduced bacterial biofilm formation but also significantly decreased the viability of the cells within the biofilm matrix. According to the results, treating with Cip alone reduced bacterial biofilms by 32%, while pretreatment with Ar-plasma for 5, 10, 30, 60, and 90 s and subsequent treatment with Cip reduced bacterial biofilms by 76%, 79%, 81%, 75%, and 88%, respectively. In addition, the viability of bacterial cells within the biofilm matrix reduced to 66% in Cip treated cells, while pretreating with Ar-plasma for 5, 10, 30, 60, and 90 s and then treating with Cip significantly decreased cell viability to 28%, 25%, 21%, 23%, and 15%, respectively. This concept opens a promising approach for the treatment of drug-resistant bacteria for decontamination of heat-sensitive materials and human tissues based on the combination of atmospheric-pressure non-thermal Ar-plasma and antibiotics.

Promise of nonthermal plasmas in addressing emerging environmental and health problems: Present and future

Nonthermal atmospheric pressure plasmas transform input electrical energy efficiently into reactive species, charged particles, and photons. This “activated gas” is being investigated as solutions for a range of environmental and health problems facing society today. In this Perspective, we take a cursory look at a few of these societal problems and the reflected role that plasmas may play in charting the pathway to a solution buoyed by supporting research. Here, we survey the plasma-based opportunities in the removal of trace contaminants in water supporting methodologies such as water reuse, which addresses scarcity and pollution, the opportunity posed by plasmas-based chemical depolymerization for plastics recycling, and the application of plasmas for food security, which includes sterilization of foodstuffs and the improvement of crop yield. Finally, we also included a short review on how plasmas may help control disease spread. In each case, the scope of the problem is presented along with the potential plasma-based solution.

Degradation of Bacterial Antibiotic Resistance Genes during Exposure to Non-Thermal Atmospheric Pressure Plasma.

Bacterial resistance to antibiotics has become a major public health problem in recent years. The occurrence of antibiotics in the environment, especially in wastewater treatment plants, has contributed to the development of antibiotic-resistant bacteria (ARB) and the spread of antibiotic resistance genes (ARGs). Despite the potential of some conventional processes used in wastewater treatment plants, the removal of ARB and ARGs remains a challenge that requires further research and development of new technologies to avoid the release of emerging contaminants into aquatic environments. Non-thermal atmospheric pressure plasmas (NTAPPs) have gained a significant amount of interest for wastewater treatment due to their oxidizing potential. They have shown their effectiveness in the inactivation of a wide range of bacteria in several fields. In this review, we discuss the application of NTAPPs for the degradation of antibiotic resistance genes in wastewater treatment.

The production of OH in a nanosecond pulsed helium plasma jet impinging on water, saline, or pigskin

Applications of plasma-induced biological effects via reactive oxygen and nitrogen species (RONS) make the non-thermal atmospheric-pressure plasma jets an appealing tool in biomedical fields. The presence of biological materials, especially as part of the electrode circuit, may change the plasma properties and impact on the production of RONS at the plasma–biomaterial interface. Effects of biomaterials on the production of hydroxyl radicals (OH) in a nanosecond pulsed, atmospheric-pressure plasma jet were investigated using a needle-to-plate electrode configuration with water, phosphate-buffered saline (PBS), or pigskin covering the ground plate. Driven by 200 ns, 7 kV pulses at 1 kHz, a helium plasma jet was generated between the hollow needle electrode and the biomaterial. Temporally resolved UV-visible imaging showed that the use of pigskin slowed down the streamer head propagation, whereas a more pronounced surface ionization wave was developed on the surface when water was used. The highest OH(A-X) emission above the biomaterial surface was observed using the PBS-covered electrode plate comparing to water or pigskin. Spatiotemporally resolved laser-induced fluorescence (LIF) showed that more OH was produced in the region near the needle electrode for both water and PBS, and the use of pigskin resulted in least OH production overall. In addition, measurements of H2O2 production in the liquid were used to determine the OH concentration in the vicinity of the biomaterial and agreed well with the relative OH-LIF measurements obtained at the gas–liquid interface for water and PBS.

Enhanced Bioremediation of 4-Chlorophenol by Electrically Neutral Reactive Species Generated from Nonthermal Atmospheric-Pressure Plasma.

4-Chlorophenol (4-CP) is a chlorinated aromatic compound with broad industrial applications. It is released into the environment as an industrial byproduct and is highly resistant to biodegradation. Pseudomonas sp. in the environment and activated sludge are used for 4-CP bioremediation; however, the degradation of 4-CP takes a long time. Consequently, the toxicity of 4-CP is a major barrier to its bioremediation. In this study, we investigated the synergistic effect of electrically neutral reactive species on the bacterial bioremediation of 4-CP. Our results showed that the concentration of 4-CP decreased from 2.0 to 0.137 mM and that it was converted to 4-chlorocatechol (4-CC; 0.257 mM), 4-chlororesorcinol (0.157 mM), hydroquinone (0.155 mM), and trihydroxy chlorobenzene and their respective ring-cleaved products following irradiation of neutral reactive species. These compounds were less toxic than 4-CP, except for 4-CC, which reduced the toxicity of 4-CP to Pseudomonas putida. When the neutral reactive species-treated 4-CP fraction was added to P. putida cultured in a synthetic sewage medium for 48 h, the 4-CP concentration was reduced to 0.017 mM, whereas nontreated 4-CP (2.0 mM) was hardly degraded by P. putida. These results suggest that the biodegradation of 4-CP can be efficiently improved by combining irradiation of neutral reactive species with microbial treatment. The irradiation of neutral reactive species of environmental pollutants may additionally lead to further improvements in bioremediation processes.