Unlocking the Synergy of Coupled Cold Plasma and Luminous Textile Photocatalysis for Indoor Air Purification: Simultaneous Elimination of Ethyl Acetate and Microorganisms

Abstract

This study investigates the simultaneous elimination of ethyl acetate (EA), a representative volatile organic compound (VOC), and Escherichia coli aerosols from indoor air using a continuous-flow dielectric barrier discharge (DBD) plasma reactor coupled with a photocatalytic luminous textile system (Cu/TiO₂-coated fibers). The effects of applied voltage, relative humidity, and air-flow rate on pollutant removal and disinfection performance were systematically evaluated. Optimal DBD operation at 18 kV, 1 m³ h⁻¹ airflow, and 70% relative humidity achieved single-process removal efficiencies of 77% for EA and 2 log reduction (CFU mL⁻¹) for E. coli. When photocatalysis was coupled with DBD plasma, a significant combined effect was observed, increasing EA degradation to 87% and bacterial inactivation to 3.8 log (CFU mL⁻¹). The coupling enhanced active-species generation, improved CO₂ selectivity (up to 53%), and reduced residual ozone concentration. Humidity positively affected microbial inactivation due to °OH radical formation but slightly decreased VOC degradation by limiting ozone regeneration. Results demonstrate the efficiency and scalability of the DBD–photocatalysis hybrid system for multi-pollutant indoor air purification, offering rapid, low-temperature treatment suitable for industrial-scale applications.

1. Introduction

In recent years, the demand for air purification technologies has increased due to worsening indoor air quality. Environmental authorities have placed growing emphasis on preventing and controlling volatile organic compound (VOC) pollution control [1,2,3,4]. As significant contributors to air pollution, VOCs have a direct impact on air quality and also take part in chemical interactions in the atmosphere leading to other contaminants, such as fine particulates and ozone [5,6,7,8]. Ethyl acetate (EA) is a VOC that is commonly utilized for food flavoring [9], chemical solvents [10] and other industrial applications. It is crucial to research methods of removing ethyl acetate because it poses a threat to both human and environmental health.

Escherichia coli (E. coli) is a common opportunistic pathogen detected in indoor air in the food industry. Endotoxins, which are commonly found in Gram-negative E. coli’s outer cell-wall membranes, have the potential to cause various negative health effects, such as chronic bronchitis, asthma, and decreased lung function [11]. To make airborne pathogens harmless for healthy inhabitants and reduce their virulence, it is important to propose air technologies that remove them as soon as possible. It is imperative that we develop new disinfecting techniques that offer benefits such as quickest treatment times, lower temperatures, the ability to handle a variety of materials, and safe operating conditions [12]. In this study, ethyl acetate and E. coli were targeted to be decomposed and inactivated respectively.

Conventional air purification methods, such as adsorption [13,14], the bio-electrochemical process [15], thermal oxidation process [16], membrane separation [17,18], and photocatalysis [19], all have drawbacks like low efficiency, secondary pollution, high technical requirements, expensive maintenance, short service life, and limited application range. In this pursuit, reactor efficiency for the simultaneous removal of two types of contaminant is the key treatment parameter. The use of non-thermal plasma for air treatment is a promising technology and alternative to conventional purification methods, as it offers the advantages mentioned above. Dielectric barrier discharge (DBD) is the most frequent form of non-thermal plasma generation that can operate at ambient temperature and atmospheric pressure. The plasma is formed by the connection of two conductive electrodes to an AC or pulsed power source. A dielectric layer is present on at least one of the DBD electrodes, preventing the formation of an arc after breakdown. The majority of DBDs are made up of short-lived filaments that are haphazardly delivered across the entire dielectric barrier. The plasma process leads to the formation of ions, electrons, and active species that can reach the contaminant surface and can eventually cause it to degrade [12].

In this study, the simultaneous degradation of EA and inactivation of E. coli were achieved using a novel continuous-flow DBD plasma reactor. Furthermore, the degradation of these pollutants was investigated using a combined plasma/photocatalysis process in a continuous tubular reactor.

To the best of our knowledge, no previous study focused on a combined plasma/photocatalysis process utilized for EA photocatalytic elimination and E. coli inactivation using Cu/TiO₂ luminous textiles in a prototype plug flow reactor. The plasma/luminous textiles coupling allow a gain in lamp volume, which improves the transfer of pollutants and therefore the contact between bacteria and radicals. This compact reactor is an easy configuration that can be explored on an industrial scale.

This study aims to ameliorate our previous research on the simultaneous elimination of EA and E. coli in batch mode [20] and a continuous reactor [21]. In this work, the degradation and biocide roles of combined plasma/Cu/TiO₂ luminous textiles against EA and E. coli in the air were estimated separately and simultaneously.

2. Materials and Methods

2.1. Target Contaminants

In the present study, two target compounds were treated, which were EA (C₄H₈O₂) and E. coli, which are commonly found in inside air in the agro-food industries. The E. coli DSM (10198–0307-001) was purchased from Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ, Braunschweig, Germany). The EA was supplied by ACROS organics (Geel, Belgium).

2.2. Plasma Rector Design

The reactor configuration and experimental setup are illustrated in Figure 1. The reactor consists of a rectangular glass column (90 cm length, 16 × 16 cm cross-section). DBD plasma was generated using two electrodes connected to a high-voltage power supply. The outer electrode was a copper grid covering the reactor, while the inner electrode was made of aluminum.

A sinusoidal high voltage (9–18 kV peak-to-peak, 50 Hz) was applied. The voltage was generated using a signal generator (BFi OPTILAS, Évry, France) and amplified with a high-voltage amplifier (TREK 30/20A, Trek, Inc., Medina, NY, USA). Electrical parameters were monitored using a digital oscilloscope (Lecroy WaveSurfer 24Xs, 200 MHz, Teledyne LeCroy, Chestnut Ridge, NY, USA).

Plasma discharge was generated in the gas phase through the formation of micro-discharges between the electrodes under high voltage, avoiding arc formation due to the dielectric barrier. These micro-discharges produce energetic electrons and reactive species.

Airflow was introduced using an air pump through a polyurethane tube connected to the reactor. This airflow enhanced the transport of reactive species and pollutants within the system.

Ethyl acetate was continuously injected using a syringe pump to maintain controlled inlet concentration. EA concentrations at the inlet and outlet were measured using gas chromatography (GC-500).

For biological experiments, E. coli aerosols were introduced using a nebulizer. Bacterial concentration at the reactor outlet was determined using a sampling cassette equipped with a 0.8 µm polycarbonate membrane. An alcohol bubbler was installed at the outlet to ensure safe deactivation of residual microorganisms.

Relative humidity was controlled using water bubblers, and monitored using a humidity sensor (Testo 445, Lenzkirch, Switzerland). Air-flow rate was regulated using a flow meter (BROOKS Instrument, Hatfield, PA, USA).

For plasma–photocatalysis coupling, luminous textile catalysts (Cu/TiO₂-coated fibers) and external UV-LED sources were integrated into the reactor. The catalysts were fixed on a stainless-steel mesh and simultaneously exposed to UV irradiation and plasma. The spacing between catalytic layers was 35 mm to ensure uniform exposure and efficient interaction between plasma species and the catalyst surface.

2.3. Pollutant Quantification

The performance of DBD plasma and the combined DBD plasma/photocatalysis system were assessed by determining the EA removal efficiency (RE) and the E. coli inactivation (A). The RE was determined using Equation (1)

$$\mathrm{R}\mathrm{E}\left(\mathrm{\%}\right)={\displaystyle \frac{{\left[\mathrm{V}\mathrm{O}\mathrm{C}\right]}_0{-\left[\mathrm{V}\mathrm{O}\mathrm{C}\right]}_{\mathrm{S}}}{{\left[\mathrm{V}\mathrm{O}\mathrm{C}\right]}_0}}{\times 10}^2$$

(1)

where ${\left[VOC\right]}_0 \mathrm{a}\mathrm{n}\mathrm{d} {\left[VOC\right]}_S$ are the inlet and the outlet EA concentrations (mg/m³), respectively.

To determine the bacterial inactivation (A), Equation (2) was used [22]:

$$A=Log\left(N_{inlet}\right)- Log\left(N_{outlet}\right)=Log\left({\displaystyle \frac{N_{inlet}}{N_{outlet}}}\right)$$

(2)

where $\left(N_{inlet}\right) \mathrm{a}\mathrm{n}\mathrm{d} \left(N_{outlet}\right)$ are the CFU numbers at the inlet and outlet of the reactor.

Four steps were followed to determine the concentration of bacteria (N, CFU/mL):

(i)

Prepare dilutions ranging from 10⁻¹ to 10⁻⁵ with tryptone salt broth.

(ii)

To achieve a specific dilution, add 2000 µL of the solution to two Petri dishes (1000 µL per Petri dish) lined with Trypan agar.

(iii)

Place all Petri dishes into an incubator at 37 °C.

(iv)

Visually examine and count the colonies produced after incubation for 24 h.

Equation (3) was used to calculate the concentration of bacteria (N, CFU/mL):

$$N= {\displaystyle \frac{{\sum }_{i=1}^{i=4}{C}_i}{{V(n}_1+0.1n_2)d}}$$

(3)

where ${\sum }_{i=1}^{i=4}{C}_i$ is the sum of the UFC number in the designated dishes; C_i is the number of colonies counted on a dish; V = 1000 µL is the volume of solution placed on the surface of the Petri dish; n₁ and n₂ are the numbers of dishes retained after the first and second dilutions, respectively; and d is the dilution ratio of the weakest retained dilution [20].

3. Results and Discussions

3.1. Characterizations of Luminous Textiles

The luminous textiles consist of two copper/titanium dioxide (Cu/TiO₂)-based optical fibers with a thickness of 1 mm, a length of 800 mm and width of 100 mm. They are provided by Brochier Technologies (UVtex^®). SEM images of luminous textile catalysts (Figure 2a–c) were examined to reveal the distribution of various material compounds. According to this analysis, TiO₂ nanoparticles have been found to be deposed on the textile fibers’ surface. Textile and optical fibers are associated with copper oxide wire, which exhibits a uniform distribution across the support with a moderate concentration of TiO₂ particulates. This configuration has the benefits of improving the absorption of light and enhancing the performance of the photocatalytic process in a compact reactor at the pilot scale.

Additional information about the luminous textiles used can be found in our previous work [20].

3.2. Removal of Pollutants by Non-Thermal Plasma

3.2.1. Influence of Voltage

Degradation and disinfection efficiencies are significantly influenced by the density of produced active species and energetic electrons in plasma. Increasing the voltage amplitude usually results in an increase in the density of active species in the plasma. The EA removal and the E. coli reduction were evaluated as a function of the applied voltage, as shown in Figure 3. An increase in degradation efficiency from 49.3% to 86.9% and bacterial inactivation from 0.1 log(CFU/mL) to 3.4 log(CFU/mL) was observed when the increase in applied voltage rose from 9 to 18 kV (Figure 3a). The same behavior was observed when both pollutants were treated simultaneously. The application of 9 to 18 kV resulted in an increase in degradation efficiency from 35.7% to 76.9% and bacterial inactivation from 0.1 log(CFU/mL) to 2.06 log(CFU/mL) (Figure 3b). This enhancement is attributed to the stronger electric field generated within the reactor at higher voltages, which improves the ionization degree. Consequently, pollutants are more susceptible to attack by radicals or electrons, leading to higher EA elimination and E. coli inactivation [23].

Comparing the degradation results for pollutants treated separately versus simultaneously revelated that the EA enhances bacterial inactivation, whereas EA elimination decreases in the presence of E. coli. For example, at 18 KV, the bacterial reduction for E. coli alone was 3.5 log(CFU/mL), while it was 2 log(CFU/mL) for the EA/E. coli mixture. The reason for these results is the damage caused to the bacterial protein by active particles generated by plasma. In reality, the byproducts generated by VOC degradation can impact bacterial cells [20]. In addition, at 18 kV, the degradation efficiency decreases from 86.9% in the absence of E. coli to 76.9% in E. coli’s presence. The found result suggests that E. coli slightly impedes EA removal, likely due to competition reactions of DBD between EA, byproducts of EA and bacteria [20]. This phenomenon may also be because of humidity, which is discussed in the following section.

In the DBD plasma process, VOCs and microorganisms are primarily transformed to carbon dioxide (CO₂) and other organic molecules. The variation in the selectivity of CO₂ is depicted in Figure 4. This parameter is calculated as follows:

$${CO}_2 Selectivity \left(\%\right)= {\displaystyle \frac{{{[CO}_2]}^{out}- {\left[{CO}_2\right]}^{in}}{4 \left[EA\right]\ast \%RE}}{10}^4$$

(4)

where ${{[CO}_2]}^{out}$ and ${\left[{CO}_2\right]}^{in}$ are the outlet and inlet concentrations of CO₂, respectively (ppm). $\left[EA\right]$ is the EA concentration (ppmv). The number 4 is the stoichiometric coefficient of the elimination reaction.

When applied voltage increases from 9 to 18 KV, CO₂ selectivity increases from 21% to 42%. More mineralization occurs when applied voltage increases due to the production of more electrons and reactive species, resulting in mineralized EA byproducts [23].

During the process of pollutant oxidation by DBD, ozone is a crucial element. The decomposition of ozone in situ leads to the formation of atomic oxygen, which interacts with contaminants. In these experiments, the amount of ozone produced had a direct effect on its concentration, as the flow rate of oxygen was kept constant at 1 m³/h.

It can be observed that the quantity of ozone increases when applied voltage is increased (Figure 4), which is due to the higher energy dissipation at higher voltages [24].

3.2.2. Influence of Humidity

Investigating the impact of relative humidity (RH) is very important because real-world applications involve ambient air that typically contains significant amounts of water. In order to examine the RH impact on simultaneous removal of EA and decontamination of E. coli, plasma tests were conducted at two different relative humidities (70% and 92%). The RH in the room air was measured to be 40%. The reactor had a relative humidity of 70% when E. coli was present and room air was fed into it. By installing a water bubbler at the entrance of the reactor that contained E. coli, the relative humidity in the reactor was raised to 92%. As shown in Figure 5, increasing RH from 70% to 92% caused EA removal efficiency to decrease from 76.9% to 65.2%, while E. coli inactivation increased from 2.06 log(CFU/mL) to 2.4 log(CFU/mL).

Several phenomena may occur due to increased humidity during a DBD process: (i) The high concentration of water molecules and air ions cause their interaction to facilitate the recombination of positive and negative ions, which results in a decrease in the overall ion concentration. These active air ions continue to react with water vapors and generate more °OH at the site of contamination. (ii) As for °OH, a similar trend can be observed for H₂O₂. Excess H₂O results in the formation of more H₂O₂. (iii) Water molecules are consumed by atomic oxygen O through the following reaction: O + H₂O ⟶ 2 OH, reducing the concentration of atomic O. It is widely acknowledged that in the DBDs, atomic O was the primary cause of the formation of O₃, O + O₂ + M ⟶ M + O₃, hence the generation of O₃ could be inhibited by water [25]. As relative humidity increased, the effectiveness of EA removal decreased, potentially because of the inhibition of O₃ regeneration. This finding suggests that O₃ is essential in the degradation of EA [26].

The decrease in EA removal efficiency at higher humidity may be attributed to the inhibition of ozone regeneration, suggesting that ozone plays a significant role in EA degradation. Conversely, numerous studies have demonstrated that reactive species such as °OH and H₂O₂ are essential for microorganism inactivation [27,28]. The °OH radical possesses a high oxidation potential, which is equal to 2.8 eV, exceeding that of other reactive species. These radicals interact directly with airborne microorganisms, playing a significant role in disinfection, whereas ozone concentration is less critical for bacterial inactivation. These findings explain the enhanced bacterial disinfection observed at higher humidity levels [25].

3.2.3. Influence of Air-Flow Rate

The impact of the air-flow rate on simultaneous EA removal and E. coli inactivation by the DBD process was investigated under the conditions of applied voltage 18 kV and relative humidity 70%. The air-flow rate was varied at 0.5, 1, and 2 m³/h. As shown in Figure 6, both EA elimination efficiency and E. coli inactivation decreased as the air-flow rate increased. Higher air-flow rates shorten the residence time of the gas mixture within the reactor. Consequently, some EA molecules and E. coli microorganisms may exit the reactor without colliding with high-energy electrons or reacting with oxidative free radicals, thereby reducing the overall degradation efficiency [29].

3.3. Removal of Pollutants by Combined Plasma Photocatalysis

In order to assess the efficiency of the coupled plasma–photocatalysis reactor, degradation studies were first performed on each pollutant separately (flow rate: 1 m³/h, frequency: 50 Hz, [EA]: 5 mg/m³, [E. coli]: 10⁴ CFU/mL). Then, the same methodology was applied when the reactor contained both pollutants simultaneously. Figure 7 shows the EA elimination rate and the E. coli inactivation obtained using a combined plasma–photocatalysis process at different plasma voltages. The experimental data indicate that increasing the applied voltage from 9 to 18 kV results in a rise in degradation efficiency from 49.2% to 86.9% and bacterial inactivation from 0.13 log(CFU/mL) to 3.5 log(CFU/mL). The same behavior was observed when both pollutants are treated simultaneously; the increase in applied voltage from 9 to 18 kV causes an increase in EA removal from 35.8% to 76.9% and bacterial removal from 0.3 log(CFU/mL) to 3.9 log(CFU/mL).The same behavior was observed when EA and E. coli were treated using only plasma processes. In fact, increasing the voltage applied to the combined reactor enhances the electric field strength, resulting in a higher degree of ionization. Thus, electrons or radicals have a higher probability of attacking the pollutant, which results in greater removal of EA and E. coli [23]. Based on the comparison of the degradation results for both pollutants separately and simultaneously, we found that EA has a greater effect on bacterial inactivation, while its elimination decreases when E. coli is present. These results are due to the damage caused to the bacterial protein by active particles generated by plasma and photocatalysis. In addition, the byproducts produced by VOC degradation can have an impact on bacterial cells [20,22]. Competitive reactions in combined plasma photocatalysis between EA, EA byproducts and bacteria can account for the slight obstacle to the removal of EA due to E. coli’s presence [20].

CO₂ selectivity and ozone generation were monitored during the combined plasma photocatalysis process, under several applied voltages from 9 to 18 kV, as shown in Figure 8. The CO₂ selectivity increases from 27% to 53%. More mineralization occurs when applied voltage increases because of the higher production of reactive species and electrons, resulting in greater mineralization of EA byproducts [23]. It can be observed that the quantity of ozone increases when applied voltage is increased (Figure 8), which is due to the higher energy dissipation at higher voltages [24].

During the process of pollutant oxidation by combining DBD plasma/photocatalysis, ozone is a crucial element. The decomposition of ozone in situ leads to the formation of atomic oxygen, which interacts with contaminants. In these experiments, the amount of ozone produced had a direct effect on its concentration, as the flow rate of air was kept constant at 1 m³/h [24].

3.4. Comparison Between Plasma, Photocatalysis, and Coupled Plasma/Photocatalysis Processes

Three processes—photocatalysis, plasma, and coupled plasma/photocatalysis—were compared for EA removal, E. coli inactivation, ozone generation, and CO₂ selectivity (Figure 9). The combined process proved most effective. At 18 kV, Figure 9a shows that the combined process achieved 87% EA removal and 3.8 log(CFU/mL) inactivation. The reactive species produced can efficiently oxidize the treated pollutants, improving their degradation. The elimination of EA and E. coli in the gas stream is attributed to both energetic electrons and atomic oxygen (O°) [23]. Combining DBD plasma with a photocatalyst improves EA and E. coli abatement over DBD plasma alone because of the increased number of reactive species. This indicates that a strong synergetic effect exists in the combined process of DBD plasma and photocatalysis for the removal of VOCs and microorganisms.

The majority of EA is converted into CO₂, along with other organic compounds, such as ethanol and acetaldehyde. E. coli is mostly converted into CO₂, H₂O, nitrogen and sulfur [20]. Figure 9b shows the variation in CO₂ selectivity during the simultaneous EA removal and E. coli inactivation. When DBD is combined with photocatalysis, the selectivity of CO₂ increases from 42% to 53%, which is noteworthy to observe. This behavior is a result of TiO₂’s photocatalytic activity. In fact, by coupling DBD and photocatalysis, the selectivity of CO₂ is improved compared to DBD alone. Additionally, the removal of EA may result in the deposition of intermediates on the photocatalyst’s surface, which can subsequently lead to mineralization. Many studies have reported similar results on isovaleraldehyde [23] and acetylene [30]. With photocatalysis, CO₂ selectivity is increased to 61%. Several studies have established that the improvement in mineralization is linked to the porosity of the medium: porosity causes gas byproducts to spend more time in the solid pore system [23,31].

Ozone plays a crucial role in the EA and E. coli oxidation. Pollutants interact with the atomic oxygen that is generated from ozone decomposition. It is worth mentioning that the photocatalytic material presence reduces the O₃ amount in the reactor’s exit from 30 ppm to 26 ppm. The output of the photocatalytic reactor did not contain any ozone. In reality, UV radiation can promote the destruction of ozone through the following reaction [32]:

$$O_3+h\mathcal{V}\left(254<\lambda <350 \mathrm{n}\mathrm{m}\right)\to O_2+°O$$

(5)

Table 1. Literature comparison of bacterial inactivation and VOC degradation using different approaches for indoor air purification.

Pollutants	Methods	Operating Parameters	Degradation Results	References
Microorganisms	Photocatalysis Ag/TiO2-NTs	[E. coli] = 4 × 106 CFU/mL Volume = 100 mL Time = 180 min	1.6 log(CFU/mL)	[33]
	Agar matrix surface + blueberry skin + UV-TiO2 and UV alone	[E. coli] = 7 log CFU/g UV intensity = 6.0 mW/cm2 Time = 30 s	3.4 logCFU/g (UV alone) 4.6 logCFU/g (UV-TiO2)	[34]
	Photocatalysis Spherical batch reactor Ag/TiO2	[VOC] = 4.4 g/m3 T = 50 at 100 °C Λ = 380–420 nm UV–vis light irradiation	Simultaneous treatment: E. coli: 99.7% (60 min) VOC: 100% (25 min)	[35]
VOCs	Photocatalysis Cu/TiO2	Air-flow rate = 1 m3/h [Butane-2,3-dione] = 10 mg/m3 H= 5% UV-A light	52%	[22]
	TiO2 fiberglass	Flow rate = 150–300 mL/min [Methyl-ethyl-ketone] = 1.5 mg/L UV light source	10%	[36]
	TiO2 Ahlström-support		40%
E-coli + EA	Photocatalysis Cu/TiO2	UV–vis light irradiation Applied voltage = 18 kV Air-flow rate = 1 m3/h RH = 70% Frequency = 50 Hz [EA] = 5 mg/m3 [E. coli] = 104 CFU/mL	Simultaneous treatment: EA: 28% E. coli: 1 log(CFU/mL)	[21]
	Plasma		Simultaneous treatment: EA: 77% E. coli: 2.06 log(CFU/mL)	This work
	Combined plasma/photocatalysis		Simultaneous treatment: EA: 87% E. coli: 3.86 log(CFU/mL)	This work

presents a comparison between the results obtained in the present study and those reported in previous works on VOC degradation and E. coli inactivation using different air-treatment processes. Most of the studies available in the literature were carried out using a single oxidation system, whereas the present work investigated a dual oxidation system. In addition, the combined plasma/photocatalysis process based on Cu/TiO₂ luminous textile demonstrated superior degradation performance compared with other reported reactor and catalyst systems. These findings highlight the potential of the combined plasma/photocatalysis process using Cu/TiO₂ luminous textile as an efficient method for the simultaneous removal of ethyl acetate (EA) and E. coli.

From a technoeconomic perspective, the plasma/photocatalysis coupling represents a promising strategy for indoor air treatment due to its high degradation efficiency, low chemical consumption, absence of secondary pollution, and potential reduction in operating time; however, challenges related to energy consumption, reactor scale-up, catalyst durability, and process optimization still need to be addressed before large-scale industrial implementation.

To summarize, plasma generates a cocktail of RONS (O, OH·, HO₂·, O₂⁻, O₃, H₂O₂, NO_x, UV, electrons), not only ozone and hydroxyl radicals; in plasma + Cu/TiO₂, the catalyst enhances local electric fields and electron density, increasing radical production and concentrating them near its surface; plasma also activates and regenerates Cu/TiO₂ (more oxygen vacancies, surface OH, modified Cu states), boosting photocatalytic oxidation; E. coli, being surface attached and surrounded by water, is more strongly affected by localized OH·/O and surface hydroxyls than volatile ethyl acetate, so the synergy is greater for bacteria; finally, humidity shifts the chemistry toward OH· and surface OH, which favors E. coli inactivation more than ethyl acetate removal, consistent with the observed stronger synergistic effect on E. coli.

4. Conclusions

The present study examined the influence of applied voltage, relative humidity, and air-flow rate on EA removal and E. coli inactivation using plasma and coupled plasma–photocatalysis processes. An increase in applied voltage significantly impacts the degradation process: (i) the EA removal efficiency is greatly increased; (ii) the E. coli inactivation is increased; (iii) the CO₂ selectivity is improved; and (iv) the generated amount of ozone is increased, because of the generation of more electrons and reactive species. In addition, the influence of applied voltage on the performance of combined DBD plasma/photocatalysis was evaluated. The same behavior was observed when studying the influence of applied voltage on the efficiency of combined DBD plasma/photocatalysis. Relative humidity is critical in the degradation of EA and E. coli during a DBD process. In addition, EA elimination and E. coli inactivation can be improved by reducing the air-flow rate, which increases the residence time of the mixed gas in the reactor. The effects of the presence of each treated pollutant on the elimination of the other were also estimated. EA enhances the inactivation of bacteria, but EA elimination decreases when E. coli is present.

Finally, comparing the three processes demonstrated that coupled plasma/photocatalysis yielded a combined effect, providing the highest efficiency for EA removal and optimal E. coli inactivation.