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Article

Non-Thermal Plasma Treatment of Dye-Contaminated Wastewater: A Sustainable Approach for Pollutant Degradation and Enhanced Plant Growth

by
Subash Mohandoss
1,
Harshini Mohan
1,
Natarajan Balasubramaniyan
1 and
Sivachandiran Loganathan
2,*
1
Laboratory of Plasma Chemistry and Physics (LPCP), Department of Chemistry, SRM Institute of Science and Technology, Kattankulathur, Chennai 603203, India
2
Department of Civil and Environmental Engineering, University of Nevada, Reno, NV 89557-0258, USA
*
Author to whom correspondence should be addressed.
Plasma 2025, 8(4), 40; https://doi.org/10.3390/plasma8040040 (registering DOI)
Submission received: 3 September 2025 / Revised: 5 October 2025 / Accepted: 8 October 2025 / Published: 11 October 2025
(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2025)
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Abstract

The win–win situation of dye degradation and nitrogen fixation in wastewater using non-thermal plasma (NTP) were investigated in this study. Specifically, the feasibility of utilizing plasma-treated dye-contaminated wastewater for seed germination and plant growth was explored. Crystal Violet (CV) and Rhodamine B (RhB) dyes were used as model pollutants, while Sorghum bicolor (great millet) seeds were used to assess germination rates and plant growth responses. In untreated wastewater containing CV and RhB, approximately 45% of seeds germinated after three days, but no significant stem or root growth was observed after 11 days. Plasma treatment significantly enhanced dye degradation, with efficiency improving as treatment time and input power increased. After 16 min of plasma treatment at 1.3 ± 0.2 W input power, about 99% degradation efficiency was achieved for both CV (0.0122 mM) and RhB (0.0104 mM). This degradation was primarily driven by reactive oxygen and nitrogen species (RONS) generated by plasma discharge. When sorghum seeds were germinated using plasma-treated wastewater, the germination rate increased to 65% after three days—20% higher than with untreated wastewater. Furthermore, after 11 days, the average stem length reached 9 cm, while the average root length extended to 7 cm. These findings highlight NTP as a promising and sustainable method for degrading textile industry pollutants while simultaneously enhancing crop productivity through the reuse of treated wastewater.

Graphical Abstract

1. Introduction

The rapid growth of industrialization and urbanization has significantly contributed to environmental pollution, particularly water pollution [1,2]. One of the major sources of water pollution is the discharge of untreated industrial wastewater, which often contains hazardous pollutants such as dyes [3]. Dyes are widely used in the textile, paper, and leather industries, and their discharge into aquatic ecosystems poses serious ecological and health risks [4,5,6]. The textile industry wastes up to 200,000 tons of dyes each year due to inefficiencies in the dyeing and finishing processes, resulting in significant environmental contamination [7]. Therefore, developing sustainable and effective methods for dye removal from wastewater is critical.
Dye-polluted water, if discharged into water bodies or agricultural lands, can adversely affect seed germination and plant growth. Many organic dyes are toxic to plants, particularly at high concentrations, disrupting cellular processes, damaging cell structures, and inhibiting enzyme function. These effects can lead to slower development, leaf chlorosis, and even plant mortality [8]. Dye-polluted water adversely affects seed germination and plant growth through mechanisms such as chemical toxicity, interference with light absorption, and disruption of nutrient balance. Synthetic dyes often contain harmful compounds including heavy metals, aromatic amines, and persistent organic pollutants. These substances can penetrate seed coats, disrupt cellular metabolism, and inhibit enzymatic activities essential for germination [9]. Moreover, such pollutants induce oxidative stress, leading to lipid peroxidation, protein denaturation, and DNA damage in developing seedlings. Dyes also absorb and scatter light in water, reducing the availability of photosynthetically active radiation (PAR), which impairs chlorophyll synthesis and stunts plant growth. Additionally, dye contamination alters water chemistry, negatively impacting soil microbial communities, disrupting nutrient cycling, and decreasing the bioavailability of essential nutrients such as nitrogen, phosphorus, and potassium. Consequently, plants exposed to dye-contaminated water often show delayed germination, poor root and shoot development, reduced biomass, and heightened vulnerability to diseases and environmental stressors ultimately resulting in lower crop yields and diminished agricultural productivity [10,11]. Furthermore, dye-polluted water can alter soil pH levels, compounding its detrimental effects on plant growth and development [12].
Various methods have been developed for dye degradation, including biological treatment, coagulation/flocculation, ultrasonic mineralization, membrane filtration, precipitation, flotation, adsorption, ion exchange, electrolysis, enzymatic degradation, and advanced oxidation processes (AOPs) [13,14]. However, due to the varying chemical structures of dyes, a single method is often insufficient for their degradation, particularly when a mixture of azo, heterocyclic, and cationic dyes is present [15]. Among these, non-thermal plasma (NTP), a promising AOP, has shown significant potential for degrading various organic pollutants, including dyes [16,17]. NTP consists of high-energy electrons, ions and reactive species that break down pollutants into smaller, less harmful compounds. Recent studies have demonstrated the effectiveness of NTP-assisted dye degradation and enhanced mineralization [18,19,20].
Crystal Violet (CV) and Rhodamine B (RhB) are two widely used dyes known for their resistance to conventional water treatment methods. However, NTP treatment has been shown to effectively degrade these dyes in water. NTP offers several advantages, including high degradation efficiency and low energy consumption. The degradation of dyes by NTP is driven by the generation of highly reactive species, such as hydroxyl radicals and ozone, which interact with dye molecules, breaking them down into less harmful substances [21]. The efficiency of NTP degradation depends on several factors such as dye type and concentration, solution pH, the treatment time, and plasma reactor type [22].
Sorghum bicolor (great millet) is a vital crop grown in arid and semi-arid regions worldwide [23]. Enhancing sorghum seed germination and plant growth is crucial for sustainable agriculture. Studies have shown that the NTP treatment of seeds can significantly improve seed germination and plant growth [24,25,26]. NTP treatment exposes seeds to high-energy electrons and ions, which can promote the release of sorghum seeds, which can promote the release of growth-regulating phytohormones, such as gibberellins, cytokinins, and auxins [27]. In this study, we investigate the application of NTP for the complete degradation of CV and RhB dyes in aqueous solutions, and assess the impact of the resulting plasma-treated water (PTW) on sorghum seed germination and early plant development. The concentrations of reactive species produced in PTW were quantified, and changes in physicochemical properties such as electrical conductivity, alkalinity, total dissolved solids (TDS), and pH were monitored. Total Organic Carbon (TOC) analysis and by-product identification were also conducted to evaluate the efficiency and completeness of the degradation process. Furthermore, the effects of varying exposure durations to PTW on seed germination rate, stem growth, and root development were examined. The physicochemical characteristic of sorghum seeds post-treatment were analyzed using high-resolution scanning electron microscopy (HR-SEM) and water contact angle measurements to understand the underlying mechanisms influencing seed response.

2. Materials and Methods

2.1. Materials

Crystal Violet (C25H30N3Cl) (Gention violet), Rhodamine B (C. I. 45170) (C28H31ClN2O3), Potassium iodide (KI), Starch soluble, sulfanilic acid (C6H7NO3S), Zinc (Zn) dust, Sodium thiosulphate pentahydrate (Na2S2O3.5H2O), N-(1-Naphthyl) ethylenediamine dihydrochloride (C12H16N2Cl2), and isopropanol (C3H8O) were purchased from Sisco Research Laboratory, India. Anhydrous di-Sodium hydrogen orthophosphate (Na2HPO4) and Potassium dihydrogen phosphate (KH2PO4) were procured from Fisher Scientific, India. Concentrated hydrochloric acid (Con. HCl) and sulphuric acid (Con. H2SO4) were purchased from Rankem Chemicals, Chennai, India. All chemicals and solvents were used without any purification.

2.2. Non-Thermal Plasma Reactors

Figure 1a–c report the general schematic of the experimental setup and the plasma reactors. Two dielectric barrier discharge (DBD) reactors were used. A cylindrical double DBD (D-DBD) reactor (Figure 1b) was employed for the water treatment, and a coaxial glass tubular reactor (Figure 1c) was used for seed treatment at atmospheric conditions.

2.2.1. Water Activation/Treatment Reactor

The DBD plasma bubbler reactor presented in Figure 1b consists of a cylindrical glass tube with a length of 230 mm, an outer diameter (OD) of 8.1 mm, an inner diameter (ID) of 5.6 mm, and a wall thickness of 1.25 mm. A copper wire with a thickness of 1.2 mm was fixed at the centre of the glass tube, serving as the high-voltage electrode. This copper wire spans a length of 220 mm, leaving a discharge gap of 2.2 mm. The discharge length was fixed at 15 mm by wrapping aluminum tape around the outer glass tube. Zero air gas, at a flow rate of 50 mL/min, was continuously supplied through the inner glass tube using a calibrated mass flow controller (MFC, KOFLOC-Make, Kyoto, Japan).

2.2.2. Seed Treatment Reactor

Figure 1c depicts a glass tube reactor with a length of 200 mm, an OD of 26 mm, an ID of 21.5 mm, and a wall thickness of 2.25 mm. A stainless steel (SS) rod, 6.5 mm thick, is positioned in the centre of the reactor, leaving a 7.5 mm discharge gap. This SS rod serves as the high-voltage electrode, while an SS mesh wrapped around the glass tube acts as the ground electrode. The discharge volume was maintained at 19 cm3 by fixing the discharge length at 100 mm. For seed treatment, the air flow rate was fixed at 500 mL/min.

2.2.3. Plasma Discharge Power Measurement

A step-up high-voltage transformer, supplied by Jayanti Transformer (Chennai, India), was used to ignite the plasma discharge. The applied voltage could be varied between 0 and 40 kV (peak to peak) at a fixed frequency of 50 Hz. Two high-voltage probes with 1:100 attenuation (Zeal Manufacturing Service Limited, Pune, India) were connected to an oscilloscope (70 MHz, 2 Ga s−1, Keysight InfiniiVision X2002A, Santa Rosa, CA, USA) to record the electrical discharge characteristics and calculate the plasma input power. The waveforms and Lissajous figures of both reactors are shown in Figures S1 and S2.

2.3. Seed and Water Treatment Procedure

About 5 ± 0.5 g of handpicked healthy sorghum seeds were packed into the tubular DBD reactor (Figure 1c). The effect of plasma treatment time (ranging from 0 to 30 min), under fixed operating conditions (applied voltage 16 kV, 50 Hz frequency and the corresponding power is 1.7 ± 0.2 W), on seed surface modification was investigated. For water treatment, 40 mL of distilled water (DW), tap water (TW), and dye-polluted water were treated by air plasma (50 mL/min, 15 kV 50 Hz, and the plasma input power is 1.3 ± 0.2 W) for 16 and 30 min.

2.4. Analytical Devices

The surface modification of Sorghum seeds due to plasma discharge was studied using a Higfh Resulation Scanning Electron Microscope (HR-SEM, Thermo Scientific Apreo S). Seed surface wettability was determined by measuring the water contact angle using a goniometer (Kyowa Interface Science Co., Ltd., DMs-401, Niiza-City, Japan). The pH, conductivity, total dissolved solid (TDS), and salinity of the water samples were measured using multi-parameter tester (PCSTestrTM 35, EUTECH instruments, Singapore). Nitrite (NO2−) and nitrate (NO3−) concentrations were measured using a UV spectrophotometer (UV, Agilent Cary 60, Ketsch, Germany).

3. Results and Discussion

3.1. Crystal Violet (CV) and/or Rhodamine B (RhB) Degradation

The degradation of individual CV and RhB dyes as well as their mixture in water via plasma treatment are reported in Figure 2. Plasma plays a crucial role in generating primary reactive species in the gas phase and at the gas–liquid interface. These highly reactive species—including electrons, ions, free radicals, and excited molecules, are transferred into the aqueous solution, where they contribute to the formation of secondary reactive species [28]. The primary reactive oxygen and nitrogen species (RONS), such as •OH, •NO, H2O2, O, and O3, are predominantly generated in the gas-phase plasma and undergo various transformations upon entering the liquid phase. When plasma discharge occurs at the liquid surface, additional RONS can also be produced within the interfacial layer of the aqueous solution.
Secondary RONS, such as •OH and •NO2 (from HOONO), as well as HNO2 and HNO3 (from •NO and •NO2), may form through the degradation or interaction of primary RONS with each of the other components in the medium [29]. Owing to the inherent reactivity of both primary and secondary species, these reactive agents work synergistically to decompose dye molecules into intermediate compounds and/or stable end products such as carbonates and formats [30]. Notably, no mechanical stirring was employed in the experimental setup, indicating that mixing within the system occurred solely via diffusion.
In Figure 2a, the UV–vis absorption spectra reveal the progressive degradation of CV over treatment times ranging from 0 to 16 min. The absorption peak at 590 nm gradually diminishes, accompanied by a noticeable fading of the dye’s colour, as shown in the photographic inset. A similar trend is observed for RhB in Figure 2b, where the absorption peak at 550 nm decreases over time under plasma exposure, indicating effective decolorization. When a mixture of CV and RhB dyes was subjected to plasma treatment, as shown in Figure 2c, a combined absorption peak at 555 nm decreased steadily during the 20 min treatment, confirming the simultaneous degradation of both dyes in the mixture. These results collectively demonstrate the high efficiency of NTP in degrading individual dyes as well as their combination in aqueous media. The gas–liquid interference is depicted in Figure 2d which illustrates the interaction of gas-phase plasma species with the liquid phase and dye molecules at the gas–liquid interface. During air plasma discharge, a variety of reactive oxygen and nitrogen species (RONS) are generated, including ozone (O3), hydroxyl radicals (•OH), atomic oxygen (O), superoxide anions (O2•−), nitric oxide (NO), and nitrogen dioxide (NO2). These species are formed primarily in the gas phase and subsequently diffuse into the plasma–liquid interface and bulk liquid phase.
Once in the liquid, these reactive species initiate oxidative and reductive reactions that target the dye molecules. Among these, hydroxyl radicals (•OH) are particularly potent, attacking the conjugated chromophore structures and disrupting π-electron delocalization, resulting in rapid decolorization. Continued oxidation leads to the fragmentation of aromatic rings and formation of intermediate products such as aldehydes, ketones, and carboxylic acids. Ultimately, these intermediates undergo further breakdown to yield final mineralization products such as into smaller, more biodegradable intermediates, and inorganic ions, with complete mineralization occurring only under extended treatment time [31]. Additionally, plasma-induced ultraviolet (UV) radiation and shockwaves further enhance degradation efficiency through photolysis and the mechanical disruption of dye molecules. The presence of microbubbles, which increase the gas–liquid interfacial area, further supports efficient mass transfer and reaction kinetics [32]. Thus, the observed colour fading and spectral changes in Figure 2 confirm the effective degradation and mineralization of CV and RhB by NTP. This approach holds considerable potential for wastewater treatment applications, offering an environmentally friendly and efficient method for removing organic pollutants from water.
The kinetic plots of the dye degradation are linear, indicating that each follows pseudo-first-order kinetics. The rate constant measures the speed of dye degradation: the higher the rate constant, the faster the degradation. The kinetic plot in Figure S3a for CV dye shows a degradation rate constant of k = 0.0166 s−1, with the concentration of CV dye decreasing exponentially over time. For RhB dye, the degradation rate constant is higher, at k = 0.0212 s−1, indicating that RhB dye degrades more rapidly, leading to a faster decrease in concentration, as shown in Figure S3b.
For the mixture of CV and RhB, the combined degradation rate constant was determined to be 0.0128 s−1, as shown in Figure S3c. This value represents the overall degradation rate of both dyes in the mixture. The rate observed for the dyes in the mixture differs from those of the individual dyes, as the coexistence of CV and RhB creates a competitive system that no longer reflects two independent degradation processes. Non-thermal plasma generates a continuous supply of reactive nitrogen and oxygen species over the treatment period. In the mixture, both CV and RhB simultaneously consume these reactive species, leading to a reduction in the steady-state concentration of radicals compared to single-dye systems. As shown in Figure S3d, the degradation rates of CV (k = 0.0344 s−1) and RhB (k = 0.0409 s−1) in the mixture are slower than when degraded individually (CV k = 0.0166 s−1 and RhB k = 0.0212 s−1). The lower overall rate observed for the mixture indicates a slower degradation process compared to single-dye systems. Therefore, optimization of NTP operating conditions is essential and we should consider the complexity of the polluted water matrix.

3.2. Dye Mineralization and By-Product Identification

Figure S4 presents the Total Organic Carbon (TOC) removal efficiency for CV, RhB, and their mixture (CV + RhB) following 30 min of plasma treatment, with an initial dye concentration of 5 mg/L. The TOC analysis reveals that 52%, 50%, and 53% of the initial organic carbon content was removed from CV, RhB, and CV + RhB solutions, respectively. These results indicate that a substantial portion of the dye molecules underwent mineralization during plasma exposure.
However, as shown in Figure 2, complete decolorization (100% colour removal) was achieved for all three dye solutions, yet residual organic content remained 48% for CV, 50% for RhB, and 47% for CV + RhB. These remaining fractions likely correspond to intermediate degradation products that retain some organic structure but lack the chromophoric groups responsible for visible colour.
To further investigate the chemical nature of these residual compounds, liquid chromatography–mass spectrometry (LC-MS) analysis was performed on the CV solution after 30 min of plasma treatment. The LC-MS chromatogram (Figure S5a) revealed several by-products based on their mass-to-charge (m/z) ratios, including Pararosaniline (m/z 293), Salicylideneaniline (m/z 198), (E)-4-(phenylimino)butan-2-ol (m/z 163), and 4-(N-methylamino)phenol (m/z 127) [33,34], as illustrated in Figure S5b. These compounds are indicative of progressive dye fragmentation through oxidative cleavage and suggest incomplete mineralization. Overall, the combined TOC and LC-MS analyses confirm that while plasma treatment effectively decolorizes the dye solutions, complete mineralization is not fully achieved within 16 min. The remaining TOC corresponds to partially oxidized intermediate products, underscoring the importance of further treatment or optimization for complete degradation of organic pollutants.

3.3. Effect of Dye-Contaminated Water on Seed Germination

Figure 3 presents a comprehensive evaluation of the effects of plasma-treated water and plasma-treated seeds on the germination behaviour of Sorghum bicolor (great millet) in the presence of dye pollutants CV and RhB. Five different irrigation media were tested: (i) tap water (TW), (ii) distilled water (DW), (iii) 0.0122 mM CV solution, (iv) 0.0104 mM RhB solution, and (v) a mixture of CV (0.0122 mM) and RhB (0.0104 mM). The detailed germination study procedure is provided in the SI file.
Figure 3a shows the images of control and plasma-treated Sorghum bicolor seeds on day 1 and day 3 of germination. For control seeds (without plasma treatment), it was observed that water contaminated with CV, RhB and the mixture of CV + RhB did not significantly affect germination. After 3 days of sowing, about 50% germination was observed across all water types, indicating that the dyes did not have a substantial impact on the early stages of germination.
Quantitative data in Figure 3b supports this observation, with germination rates of control seeds ranging from ~47% to 51% across all water types. In contrast, Figure 3c reveals that plasma-treated seeds (PTS) exhibited notably enhanced germination rates (57–65%), regardless of the water quality. This improvement is due to the plasma treatment’s ability to modify seed surface properties, enhancing water uptake and metabolic activation.
The findings align with prior reports. For example, Mohandoss et al. (2024) observed a 75% germination rate for plasma-treated pearl millet seeds using tap water [25], while Sivachandiran and Khacef (2017) reported ~60% for radish under similar plasma conditions [24]. These results suggest that seed surface properties, rather than moderate pollutant exposure, play a more crucial role in initiating germination.
Plasma treatment induces physical and chemical changes on the seed surface through exposure to reactive oxygen and nitrogen species (RONS), UV photons, and energetic electrons [35,36]. These interactions cause micro-etching, increase surface roughness, and introduce hydrophilic functional groups such as hydroxyl and carboxyl groups. These modifications enhance seed wettability and permeability, which improve water absorption and facilitate enzymatic and metabolic activities essential for germination [37,38].
In conclusion, the image in Figure 3 illustrates that plasma treatment, whether applied to seeds or water, can significantly improve germination outcomes even under mildly polluted conditions, highlighting the potential of plasma technology for sustainable agriculture and environmental resilience.
Furthermore, plasma-induced alterations in surface charge distribution can influence seed–soil interactions, potentially enhancing adhesion and promoting better nutrient uptake. High-resolution scanning electron microscopy (HR-SEM) images of control and plasma-treated Sorghum bicolor seeds, shown in Figure 4, reveal distinct morphological differences induced by plasma treatment. Control seeds (Figure 4a–c) exhibit smooth and relatively flat surfaces, whereas plasma-treated seeds (Figure 4d–f) display roughened textures with pronounced fissures and microcracks.
These morphological changes result from the interaction of energetic electrons, reactive species, and localized heating generated during air plasma discharge. Such interactions cause physical etching and chemical modifications on the seed surface, contributing to both short- and long-term changes in surface properties that enhance water absorption and metabolic activity.
To further assess the impact of plasma treatment on surface hydrophilicity, water contact angle (WCA) measurements were conducted using 5 μL droplets of distilled water on both control and plasma-treated seeds (PTS). Each measurement was repeated three times, and contact angles were analyzed using Image J software (ver. 1.52a). As shown in Figure 5, control seeds exhibited an average WCA of 120.1°, indicative of a hydrophobic surface. In contrast, plasma treatment significantly reduced the contact angle to 91.5°, representing a 23.8% decrease and indicating enhanced surface wettability.
These surface modifications correlate well with the improved germination performance observed in plasma-treated seeds. As reported in Figure 3b, control seeds watered with tap water (TW), distilled water (DW), and dye-contaminated water (CV and RhB) showed germination rates around 42–50% by day 3. However, plasma-treated seeds achieved higher germination rates (~57–62%) across all water types, including those contaminated with dyes Figure 3c. This suggests that the plasma-induced changes to surface morphology and hydrophilicity play a more critical role in enhancing germination than the presence of low concentrations of dye pollutants.

3.4. Effects of Dye-Contaminated Water on Post-Germination Plant Growth

To evaluate the effects of dye-contaminated water on post-germination plant growth, Sorghum bicolor seedlings were cultivated using tap water (TW), distilled water (DW), and water containing CV, RhB, and their mixture. Figure 6 presents visual and quantitative comparisons of mean root length (MRL) and mean stem length (MSL) development in both control (a) and plasma-treated seeds (b), 11 days after sowing.
From the photographic images, it is evident that control seeds watered with TW and DW exhibited robust growth, characterized by long roots and stems. In stark contrast, those watered with CV, RhB, or their mixture showed severely stunted development, with root lengths often below 0.2 cm and minimal stem elongation. Plasma-treated seeds (PTS), however, demonstrated notably improved growth across all conditions, including those involving dye exposure.
The quantitative data, summarized in Figure 3c and Figure 6c, further confirm these observations. For control seeds, the average stem lengths under TW, DW, CV, RhB, and CV + RhB were 14.0 cm, 13.9 cm, 2.2 cm, 2.1 cm, and 2.2 cm, respectively. Corresponding root lengths were 8.3 cm, 8.0 cm, and only 0.2 cm for all dye treatments. Plasma-treated seeds outperformed controls under all conditions: stem lengths reached 15.0 cm (TW), 14.8 cm (DW), 3.0 cm (CV), 4.0 cm (RhB), and 3.5 cm (CV + RhB), while root lengths were 12.5 cm, 11.0 cm, and 0.5 cm for all dye treatments, respectively.
These results clearly indicate that while dye-contaminated water inhibits plant growth, plasma treatment can partially mitigate this phytotoxicity, enhancing root and stem elongation even under pollutant stress. Among the dyes tested, CV had a more pronounced inhibitory effect, consistent with its known toxicity profile. CV, a triphenylmethane dye, is notorious for generating reactive oxygen species (ROS) that induce oxidative stress, damaging cellular components such as DNA, lipids, and proteins. This stress impairs vital processes such as water uptake, cell division, and metabolic function, ultimately stalling plant development.
Moreover, CV disrupts microbial communities essential for nutrient cycling and can hinder photosynthetic activity by obstructing light penetration. Parshetti et al. reported similar phytotoxic effects of CV on Sorghum bicolor, Vigna radiata, Lens culinaris, and Triticum aestivum, noting reductions in germination rates and seedling lengths. CV has also been identified as a mitotic poison, clastogen, and potential carcinogen with significant environmental hazards [39,40].
Rhodamine B (RhB), though moderately toxic, also impairs plant growth. It can disrupt cell division, reduce chlorophyll a and b, carotenoids, and overall protein synthesis. Sharma et al. further observed that RhB exposure alters antioxidant enzyme activity and diminishes chlorophyll content in a concentration-dependent manner [41,42]. Dye pollutants, especially CV, significantly suppress plant growth, but plasma treatment shows promise in improving seedling resilience against such chemical stressors.

3.5. Seed Germination Using Plasma-Treated Water Contaminated with CV and RhB

The impact of plasma-treated water (containing degraded CV and/or RhB) on sorghum seed germination is presented in Figure 7. To evaluate the effect of plasma degradation on seed germination, two treatment durations of 16 and 30 min were used. Figure 7a,b show the germination rates of control and PTS, respectively, when watered with solutions treated for 16 min. By day three, control seeds watered with 16 min plasma-treated tap water (TW) and distilled water (DW) showed germination rates of 45% and 50%, respectively. Seeds watered with plasma-treated CV, RhB, and CV + RhB solutions had germination rates of 43%, 46%, and 45%, respectively. In contrast, plasma-treated seeds irrigated with the same water types exhibited slightly higher germination rates: 52% (TW), 55% (DW), 53% (CV), 54% (RhB), and 50% (CV + RhB).
Figure 7c,d show the results when the treatment duration was extended to 30 min. For control seeds, germination rates were 62% (TW), 64% (DW), 60% (CV), 57% (RhB), and 53.3% (CV + RhB). Interestingly, plasma-treated seeds watered with these solutions exhibited germination rates of 64% (TW), 64% (DW), 61% (CV), 66.6% (RhB), and 58% (CV + RhB).
Plasma treatment of water containing CV and RhB promotes seed germination by combining detoxification, molecular degradation, and nutrient enrichment. The NTP generates reactive species such as hydrogen peroxide (H2O2), ozone (O3), and hydroxyl radicals (•OH) that degrade complex dye molecules into less toxic, smaller compounds. These changes reduce the cytotoxic and genotoxic effects of the dyes on plant cells. Furthermore, NTP enhances the formation of biologically beneficial species like nitrates (NO3−) and nitrites (NO2−), contributing to improved plant nutrition and seedling resilience.
Table 1 presents the physicochemical properties of untreated and plasma-treated waters. As plasma treatment time increased, pH decreased, while conductivity, salinity, and total dissolved solids (TDS) increased, indicating increased ionization and breakdown of larger organic molecules. The reduction in pH is attributed to the formation of acidic species, including nitric acid (HNO3) and nitrous acid (HNO2), due to interactions involving reactive oxygen and nitrogen species (RONS). It can be proposed that even though the NO2− and NO3− acids are quantified, a complete analysis is needed to establish the relation between the decrease in pH and the amount of acid produced. To demonstrate this, we calculated the molar concentrations of H+ ions, provided in Table 1, and the NO2− and NO3− ion concentrations, reported in Table 2. If acidification of plasma-activated water was largely caused by the production of nitrous and nitric acids, then the concentration of H+ and the sum of NO2− and NO3− ions should be equal. However, as reported in Table 2, the NO3− concentrations are about two orders of magnitude lower than the H+ ion concentration. This finding emphasis the fact that in addition to NO2− and NO3−, additional reactive species, particularly singlet oxygen-derived unidentified species, contribute significantly to the acidification of the solution. Similar observations were reported by Brisset et al. [43] in corona discharge experiments in air above aqueous surfaces and by Sivachandiran et al. [24] in DBD bubble plasma systems. Increased conductivity and salinity are primarily due to the production of ionic species such as H2O2, NO3−, NO2−, and peroxynitrite (OONO−) [44,45,46].
It is evidenced that the plasma-treated water consistently improved seed germination compared to untreated dye-contaminated water, demonstrating the detoxifying effect of plasma on harmful dye compounds.

3.6. Effect of Plasma-Treated Water Contaminated with CV and RhB on Post-Germination Plant Growth

To evaluate the effects of plasma-treated water (containing degraded CV and/or RhB) on post-germination plant growth, Sorghum bicolor seedlings were cultivated using tap water (TW), distilled water (DW), and water containing CV, RhB, and their mixture. Figure 8 presents visual comparisons of root and stem development in both control (a and c) and plasma-treated seeds (b and d), 11 days after sowing. The visual comparison suggests that seedlings irrigated with plasma-treated water, particularly TW and DW, exhibited enhanced root and shoot development compared to untreated controls. Notably, plasma-treated dye solutions also promoted growth, albeit to a lesser extent, indicating partial detoxification of the dyes via plasma treatment. The reactive oxygen and nitrogen species (RONS) produced by plasma play a significant role in promoting this growth [47]. Plasma-treated seeds demonstrated significantly enhanced stem and root growth compared to untreated seeds, regardless of the water type used. These findings suggest that the initial plasma treatment promoted early seedling development by modifying the seed surface through plasma-generated reactive species, leading to improved water uptake and growth.
The quantitative data, summarized in Figure 9a,b presents the root and stem length profiles of control and plasma-treated seeds watered with 16 min plasma-treated TW, DW, CV, RhB, and (CV + RhB) solutions. In the control seeds, the average stem lengths were 14.1 cm, 14.3 cm, 8 cm, 8.3 cm, and 8.5 cm, respectively, while the average root lengths were 9.5 cm, 9 cm, 6 cm, 7.7 cm, and 7.2 cm, as reported in (Figure 9a). For plasma-treated seeds, the average stem lengths were 15.2 cm (TW), 15.5 cm (DW), 10.2 cm (CV), 10.5 cm (RhB), and 10.7 cm (CV + RhB), with corresponding average root lengths of 12 cm (TW), 9.5 cm (DW), 7 cm (CV), 8 cm (RhB), and 8.3 cm (CV + RhB), as seen in (Figure 9b).
Additionally, (Figure 9c,d) display the root and stem length profiles of control and plasma-treated seeds watered with 30 min plasma-treated TW, DW, CV, RhB, and (CV + RhB) solution. In the control seeds, the average stem lengths were 14.5 cm, 14.5 cm, 10 cm, 10.5 cm, and 10.7 cm, respectively, while the average root lengths were 9.8 cm, 6.1 cm, 8.8 cm, 8.5 cm, and 9 cm, as reported in (Figure 9c). Notably, in plasma-treated seeds, the average stem lengths were 16.4 cm (TW), 16.7 cm (DW), 11.2 cm (CV), 11.5 cm (RhB), and 11.8 cm (CV + RhB), and the average root lengths were 11.5 cm (TW), 11 cm (DW), 9.5 cm (CV), 9.2 cm (RhB), and 9.4 cm (CV + RhB), as shown in (Figure 9d).
A strong correlation between the water matrix and stem and root lengths was observed. Interestingly, although plasma treatment did not completely mineralize the dyes, the fragmentation significantly reduced their original toxic effects on plant growth. Moreover, the 30 min plasma treatment significantly enhanced stem and root growth compared to the 16 min treatment.
The nitrate, nitrite and hydrogen peroxide concentrations were quantified using the UV absorption method [25], and the detailed procedure provided in the SI file. These compounds act as natural fertilizers, enhancing plant growth. These species act as natural fertilizers and help the production of amino acids, proteins, and chlorophyll, which directly support the growth of both shoots and roots. Simultaneously, the concentrations of RONS serve as signalling molecules that activate antioxidant defences, stimulate cell wall-loosening enzymes, and modulate auxin-related pathway processes essential for continuous root elongation and shoot development. Moreover, the mild surface oxidation caused by plasma treatment solution enhances the hydrophilicity of seeds or root surfaces, facilitating water absorption and stimulating the activity of metabolic enzymes necessary for energy release and cellular growth [48,49]. The combined processes of dye detoxification, nutrient enrichment, and RONS-mediated signalling provide a beneficial biochemical environment, leading to markedly improved shoot and root development in comparison to untreated dye solutions.
The concentrations of NO2−, NO3− and H2O2 in the plasma-treated wastewater are shown in Table 2. Irrespective of the water nature, we observed that increase in plasma treatment has potentially increased the concentration of NO2− and NO3− ions. The presence of these species in plasma-treated wastewater demonstrates the potential for agricultural applications, promoting plant growth without the need for chemical fertilizer. This technology supports reduced carbon emissions and fosters healthier ecosystems by minimizing chemical fertilizer usage in agriculture. Adopting such environmentally friendly practices aligns with global efforts to promote sustainable agriculture, food security, and responsible environmental management.
The presence of dye molecules enhanced the production of ROS and RNS in the solution under similar operating conditions, compared to DI water, as reported in Table 2. Interestingly, the production of these species increased with longer plasma treatment times. Therefore, it can be proposed that optimizing plasma operating conditions could significantly enhance seed germination and plant growth, even in water containing pollutants.
It is evidenced that the plasma treatment of dye-contaminated water initiates a dual mechanism: (i) the degradation of dye molecules into less toxic intermediates, thereby alleviating chemical stress on seedlings, and (ii) the enrichment of the water with biologically active reactive oxygen and nitrogen species (RONS) that serve as signalling molecules and growth enhancers. In this context, nitrate (NO3−) serves as an accessible nitrogen source, hydrogen peroxide (H2O2) may activate antioxidant defences and augment water absorption, while nitrite (NO2−) may promote enhanced nutritional digestion. These methods together transform harmful dye effluents into irrigation water that sustains and promotes plant growth.

3.7. Effect of pH on Seed Germination and Plant Growth

Figure 10 reports the quantitative data on the effect of pH (varied between 2 and 7.1 pH) on the germination of control seeds, monitored over five days after sowing. Remarkably, after one day of sowing, there were no significant effects on the seed germination for all pH studied. After five days of sowing, the germination rates increased with the increase in pH. For example, about 79% was achieved for pH 2, 73% for pH 2.5, 73% for pH 3, 79% for pH 3.5, 80% for pH 4, 79% for pH 4.5, 82% for pH 5, and 84% for pH 5.5 compared to 82% in distilled water (pH 7.1) as shown in Figure 10.
Although the differences in germination rates remained minimal after five days, a significant difference in plant growth was observed, as shown in Figure 11a. The photographic visualization, the pH of the solutions affected both root and stem lengths, indicating that while germination rates remained similar, plant growth varied considerably depending on the pH level.
The root and shoot growth profiles of control seeds watered with pH-adjusted solutions are shown in Figure 11b. All pH solutions resulted in root lengths of less than 0.5 cm, compared to distilled water, which had a root length of 7.9 cm. Stem lengths for the pH solutions were 1.4 cm (pH 2), 1.9 cm (pH 2.5), 2.3 cm (pH 3), 2.8 cm (pH 3.5), 3.8 cm (pH 4), 3.3 cm (pH 4.5), 4 cm (pH 5), 4.5 cm (pH 5.5), and 13.9 cm (DW).
The impact of acidic pH solutions on plant development can be considerable and negative, particularly in the pH range of 2 to 5.5. The low pH levels can affect nutrient availability, limiting plant access to essential elements such as nitrogen, phosphorus, and potassium [50], which can inhibit growth and impair overall plant vigour. The acidic conditions can damage root cells, reducing their capacity to absorb water and nutrients efficiently [51].
According to Pham et al., Soybean plants exposed to simulated acid rain (SAR) at pH levels of 3.0 to 6.0 (control) showed significant declines in growth and yield. Germination rate, stem length, main branches, chlorophyll content (SPAD), leaf area index (LAI), and yield components decreased as acidity increased, with the most severe effects observed at pH 3.0. Adverse impacts became prominent at pH 3.5 and below [52].
Turner et al. evaluated the seed germination and seedling growth of Paulownia tomentosa across a pH range of 1.5–7.0 to assess its suitability for acidic strip-mine reclamation. Germination failed below pH 4.0, and seedling emergence and growth were significantly hindered at pH 4.5, showing reduced root length, leaf number, and dry mass compared to pH 5.5 and 6.5. While P. tomentosa invades strip-mine areas, its establishment is likely limited to less acidic microsites [53].
As reported in Table 1, after 30 min of plasma treatment, the pH of the dye-polluted water decreased to 2.6. However, the average stem and root lengths were about 10 cm and 7.4 cm, respectively, six times greater than the control seeds watered with a 2.5 pH solution. This confirms that despite the pH decrease after 30 min of plasma treatment, the plasma-treated solution, with RON and ROS, had a positive effect on plant growth.
The artificial acidic pH of irrigation water with HCl (only to increase the pH without bringing any potential nutrition such as NO2−, NO3− and SO42−) inhibited sorghum growth, but it had little impact on germination percentage. Growth inhibition at pH (2–5.5) correlates with diminished nutrient availability, compromised root absorption, and cellular damage due to elevated proton concentrations. Unexpectedly, plasma-treated dye solutions with similar pH levels (2.6–5.5) did not impede development. Seedlings irrigated with plasma-treated acidic solutions exhibited roots six times longer than those irrigated with HCl-acidified solutions at comparable pH levels. Several mechanisms could explain why plasma-treated solutions with acidic pH values (2.6–5.5) did not negatively impact plant development. First, non-thermal plasma treatment can generate RNOS, which act as signalling molecules to promote plant growth. These species can enhance the plants’ antioxidant defences, improving stress tolerance. Additionally, plasma-treated solutions may contain beneficial ions and compounds absent in HCl-prepared acid solutions, which may contribute to better plant development. On the other hand, HCl-prepared acidic solutions introduce high concentrations of hydrogen ions into plant cells, disrupting pH balance and interfering with essential physiological processes. This sudden pH shift can damage cell membranes, inhibit nutrient uptake, and disrupt enzymatic activities critical for plant growth.
It is evidenced that the plasma-treated acidic waters stem from the synergistic action of plasma-generated RNOS, which mitigate the physiological stress often linked to low pH conditions. In contrast to HCl acidification, plasma treatment generates reactive oxygen species (ROS) and reactive nitrogen species (RNS) that serve as regulatory molecules, augmenting enzymatic activity, promoting root cell elongation, and upregulating antioxidant defence mechanisms. Furthermore, plasma-induced species may chelate or transform nutrients into more accessible forms, mitigating the nutritional solubility constraints of acidic environments. Consequently, the biological effects of acidity in plasma-treated water are fundamentally distinct from those of chemically acidified water.

4. Conclusions

In this study, the effect of cold plasma discharge on the degradation of CV, RhB and a mixture of CV + RhB dyes, as well as on sorghum seed germination and plant growth, were investigated. The dye degradation efficiency increased with treatment times, achieving about 99% degradation for both CV and RhB within 16 min. The degradation of CV and RhB, under NTP discharge, was primarily initiated and controlled by the reactive oxygen species (ROS).
Plasma-treated dye-contaminated wastewater was utilized for sorghum seed germination, leading to an enhanced germination rate and improved plant growth. After three days of sowing, about 65% germination was reached, which is 20% higher than the germination obtained with distilled water. On the one hand, the pH of the water has not affected the seed germination; however, it has significantly controlled the plant growth. On the other hand, despite the pH of the plasma-treated water varying between 2.6 and 5.7, it has not shown any negative effect on neither seed germination nor plant growth. It was demonstrated that the developed NTP reactors could be used to treat industrial effluents, and that the treated water has potential use in agricultural applications.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/plasma8040040/s1, Figure S1. (a) Wave form of applied and discharge voltage, (b) Lissajous figure for Water treatment reactor (Figure 1b). The operating conditions are: 15 kV applied voltage, and 50 Hz frequency, the corresponding plasma input power is 1.3 W. Figure S2. (a) Wave form of applied and discharge voltage, (b) Lissajous figure for seed treatment reactor (Figure 1c). The operating conditions are: 16 kV applied voltage, and 50 Hz frequency, the corresponding plasma input power is 1.7 W. Figure S3. Kinetic plot illustrating the degradation process under the assumption of pseudo-first-order kinetics. (a) CV dye (k = 0.0166 S−1), (b) RhB dye (0.0212 S−1), (c) a mixture of CV + RhB (0.0128 S−1) and (d) the degradation rates of each dye in the mixture (CV 0.0344 s−1 and RhB 0.0409 s−1). Figure S4. TOC of the 16 min plasma-treated dye solutions. Figure S5. (a) LC chromatogram of 30 min Plasma treated Crystal violet; (b) identified intermediate during CV plasma degradation. Figure S6. Effect of water matrices on control and plasma-treated Sorghum seedling growth images after day 1 and day 3. (a) watered with 16 min plasma treated water and (b) watered with 30 min plasma treated water. (Plasma operating conditions: 15 kV and 50 Hz; Seeds were treated for 30 min under air, Plasma operating conditions: 16 kV and 50 Hz).

Author Contributions

S.M. designed the experiments, drafted the manuscript, and prepared the figures. H.M. conducted formal analysis, review and editing. N.B. edited and refined this manuscript. S.L. conceived, designed, acquired funding, drafted, and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

The authors greatly acknowledge the financial support of the Science and Engineering Research Board, Department of Science and Technology, Government of India (SERB, File No. ECR/2016/001457).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Essential data is provided in the Supplementary Material, while additional information can be made available upon a reasonable request.

Acknowledgments

We acknowledge SRMIST for the high-resolution scanning electron microscope (HRSEM) facility. We acknowledge the Nanotechnology Research Centre (NRC) and SRMIST for providing the research facilities.

Conflicts of Interest

The authors declare that they have no competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. (a) Schematic of the experimental setup; (b) dielectric barrier discharge (DBD) bubbler reactor for water activation/treatment; (c) coaxial DBD reactor for sorghum seed treatment.
Figure 1. (a) Schematic of the experimental setup; (b) dielectric barrier discharge (DBD) bubbler reactor for water activation/treatment; (c) coaxial DBD reactor for sorghum seed treatment.
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Figure 2. UV-vis absorption spectra of (a) CV (absorption maxima @ 590 nm); (b) RhB (absorption maxima @550 nm); and (c) mixture of CV + RhB (absorption maxima @555 nm), and (d) reactive species production in plasma discharge at the gas–liquid interface.
Figure 2. UV-vis absorption spectra of (a) CV (absorption maxima @ 590 nm); (b) RhB (absorption maxima @550 nm); and (c) mixture of CV + RhB (absorption maxima @555 nm), and (d) reactive species production in plasma discharge at the gas–liquid interface.
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Figure 3. (a) Images of seed germination of control and plasma-treated seeds watered with various types; (b) germination rate of control seeds, and (c) germination rate of plasma-treated seeds. Plasma treatment conditions: 30 min, air, 500 mL/min, 16 kV and 50 Hz.
Figure 3. (a) Images of seed germination of control and plasma-treated seeds watered with various types; (b) germination rate of control seeds, and (c) germination rate of plasma-treated seeds. Plasma treatment conditions: 30 min, air, 500 mL/min, 16 kV and 50 Hz.
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Figure 4. HR-SEM image of (a–c) control seeds (without plasma treatment), and (d–f) plasma-treated seeds (seeds were treated for 30 min under air, plasma input voltage: 16 kV and 50 Hz).
Figure 4. HR-SEM image of (a–c) control seeds (without plasma treatment), and (d–f) plasma-treated seeds (seeds were treated for 30 min under air, plasma input voltage: 16 kV and 50 Hz).
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Figure 5. Water contact angle of sorghum control seeds (a–c), and plasma-treated seeds (d–f) (seeds were treated for 30 min under air, plasma input voltage: 16 kV and 50 Hz).
Figure 5. Water contact angle of sorghum control seeds (a–c), and plasma-treated seeds (d–f) (seeds were treated for 30 min under air, plasma input voltage: 16 kV and 50 Hz).
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Figure 6. Growth performance of Sorghum bicolor seedlings 11 days after sowing. (a) Control seeds; (b) plasma-treated seeds (PTS); (c) average stem and root lengths of control seedlings; (d) average stem and root lengths of plasma-treated seedlings. Seeds were exposed to air plasma at 16 kV for 30 min with an airflow rate of 500 mL/min prior to sowing.
Figure 6. Growth performance of Sorghum bicolor seedlings 11 days after sowing. (a) Control seeds; (b) plasma-treated seeds (PTS); (c) average stem and root lengths of control seedlings; (d) average stem and root lengths of plasma-treated seedlings. Seeds were exposed to air plasma at 16 kV for 30 min with an airflow rate of 500 mL/min prior to sowing.
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Figure 7. Effect of plasma-treated water on sorghum seed germination rate. (a) Control seeds watered with 16 min plasma-treated solutions. (b) Plasma-treated seeds (PTS) watered with 16 min plasma-treated solutions. (c) Control seeds watered with 30 min plasma-treated solutions. (d) Plasma-treated seeds watered with 30 min plasma-treated solutions. (Plasma treatment was conducted under air at 15 kV and 50 Hz for water and 16 kV and 50 Hz for seed treatment).
Figure 7. Effect of plasma-treated water on sorghum seed germination rate. (a) Control seeds watered with 16 min plasma-treated solutions. (b) Plasma-treated seeds (PTS) watered with 16 min plasma-treated solutions. (c) Control seeds watered with 30 min plasma-treated solutions. (d) Plasma-treated seeds watered with 30 min plasma-treated solutions. (Plasma treatment was conducted under air at 15 kV and 50 Hz for water and 16 kV and 50 Hz for seed treatment).
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Figure 8. Image of sorghum seedlings harvested after 11 days of sowing. (a) Control seed with 16 min plasma-treated water, (b) PTS with 16 min plasma-treated water, (c) control seed with 30 min plasma-treated water, and (d) PTS with 30 min plasma-treated water (16 kV and 50 Hz).
Figure 8. Image of sorghum seedlings harvested after 11 days of sowing. (a) Control seed with 16 min plasma-treated water, (b) PTS with 16 min plasma-treated water, (c) control seed with 30 min plasma-treated water, and (d) PTS with 30 min plasma-treated water (16 kV and 50 Hz).
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Figure 9. Average root and stem length of sorghum seedlings harvested on the 11th day after sowing. (a) Control seed with 16 min plasma-treated water, (b) PTS with 16 min plasma-treated water, (c) control seed with 30 min plasma-treated water, and (d) PTS with 30 min plasma-treated water (16 kV and 50 Hz).
Figure 9. Average root and stem length of sorghum seedlings harvested on the 11th day after sowing. (a) Control seed with 16 min plasma-treated water, (b) PTS with 16 min plasma-treated water, (c) control seed with 30 min plasma-treated water, and (d) PTS with 30 min plasma-treated water (16 kV and 50 Hz).
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Figure 10. Effect of pH on sorghum seed germination rate.
Figure 10. Effect of pH on sorghum seed germination rate.
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Figure 11. Effect of pH on sorghum seed plant growth; (a) image of sorghum seedlings; (b) average root and stem length of sorghum seedlings harvested on the 11th day after sowing.
Figure 11. Effect of pH on sorghum seed plant growth; (a) image of sorghum seedlings; (b) average root and stem length of sorghum seedlings harvested on the 11th day after sowing.
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Table 1. Physiochemical properties of control and plasma-treated water and dye contaminated solutions.
Table 1. Physiochemical properties of control and plasma-treated water and dye contaminated solutions.
pHH+ Ion
(mol/L)		Conductivity (μS/cm)Total Dissolved Solid (TDS) (ppm)Salinity (ppm)
TW7.4 ± 0.23.9 × 10−81032 ± 6745 ± 5.5522.6 ± 6.1
TW (16 min PT)6.8 ± 0.21.5 × 10−71324 ± 7893 ± 7.6644 ± 5.5
TW (30 min PT)6.5 ± 0.23.1 × 10−71459 ± 4998 ± 4.9711 ± 6.1
DW7.1 ± 0.27.9 × 10−825 ± 215.9 ± 2.322.2 ± 2.3
DW (16 min PT)3.3 ± 0.25.0 × 10−458 ± 345.2 ± 2.933.4 ± 2.4
DW (30 min PT)2.6 ± 0.22.5 × 10−3114 ± 389.4 ± 4.875.4 ± 2.0
CV5.7 ± 0.21.9 × 10−619 ± 314.6 ± 1.216.6 ± 1.8
CV (16 min PT)3.6 ± 0.22.4 × 10−478 ± 652.5 ± 5.540 ± 1.7
CV (30 min PT)2.8 ± 0.21.5 × 10−3104 ± 562.7 ± 4.654.5 ± 2.7
RhB5.7 ± 0.21.9 × 10−610 ± 16.8 ± 1.216.3 ± 1.6
RhB (16 min PT)4.1 ± 0.27.9 × 10−557 ± 440.4 ± 4.735.1 ± 3.7
RhB (30 min PT)3.4 ± 0.23.9 × 10−4105 ± 569 ± 5.850.4 ± 5.3
RhB + CV5.4 ± 0.23.9 × 10−618 ± 213.3 ± 1.716.9 ± 1.6
RhB + CV (16 min PT)3.6 ± 0.22.5 × 10−470 ± 551.6 ± 4.444 ± 3.6
RhB + CV (30 min PT)2.8 ± 0.21.5 × 10−3100 ± 672.7 ± 4.554.4 ± 3.1
Table 2. The concentration of reactive species produced.
Table 2. The concentration of reactive species produced.
Plasma Treatment TimeNO2− (mol/L)NO3− (mol/L)H2O2 (mol/L)
TWBDL *BDL *BDL *
TW (16 min PT)6.08 × 10−72.4 × 10−59.9 × 10−5
TW (30 min PT)3.4 × 10−63.8 × 10−51.2 × 10−4
DWBDL *BDL *BDL *
DW (16 min PT)1.6 × 10−62.4 × 10−59.9 × 10−5
DW (30 min PT)1.7 × 10−64.1 × 10−51.2 × 10−4
CVBDL *BDL *BDL *
CV (16 min PT)1.6 × 10−64.1 × 10−51.23 × 10−4
CV (30 min PT)4.0 × 10−66.6 × 10−51.9 × 10−4
RhBBDL *BDL *BDL *
RhB (16 min PT)1.6 × 10−64.1 × 10−51.23 × 10−4
RhB (30 min PT)2.8 × 10−64.8 × 10−51.7 × 10−4
RhB + CVBDL *BDL *BDL *
RhB + CV (16 min PT)2.0 × 10−63.7 × 10−51.76 × 10−4
RhB + CV (30 min PT)4.9 × 10−67.2 × 10−51.7 × 10−4
* BDL, below detection limit.
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MDPI and ACS Style

Mohandoss, S.; Mohan, H.; Balasubramaniyan, N.; Loganathan, S. Non-Thermal Plasma Treatment of Dye-Contaminated Wastewater: A Sustainable Approach for Pollutant Degradation and Enhanced Plant Growth. Plasma 2025, 8, 40. https://doi.org/10.3390/plasma8040040

AMA Style

Mohandoss S, Mohan H, Balasubramaniyan N, Loganathan S. Non-Thermal Plasma Treatment of Dye-Contaminated Wastewater: A Sustainable Approach for Pollutant Degradation and Enhanced Plant Growth. Plasma. 2025; 8(4):40. https://doi.org/10.3390/plasma8040040

Chicago/Turabian Style

Mohandoss, Subash, Harshini Mohan, Natarajan Balasubramaniyan, and Sivachandiran Loganathan. 2025. "Non-Thermal Plasma Treatment of Dye-Contaminated Wastewater: A Sustainable Approach for Pollutant Degradation and Enhanced Plant Growth" Plasma 8, no. 4: 40. https://doi.org/10.3390/plasma8040040

APA Style

Mohandoss, S., Mohan, H., Balasubramaniyan, N., & Loganathan, S. (2025). Non-Thermal Plasma Treatment of Dye-Contaminated Wastewater: A Sustainable Approach for Pollutant Degradation and Enhanced Plant Growth. Plasma, 8(4), 40. https://doi.org/10.3390/plasma8040040

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