Catalytic and Non-Catalytic Treatment of Industrial Wastewater under the Exposure of Non-Thermal Plasma Jet

: Freshwater is only 2.5% of the total water on the Earth and rest is contaminated or brackish. Various physical and chemical techniques are being used to purify the contaminated water. This study deals with catalytic plasma treatment of contaminated water collected from di ﬀ erent sites of Faisalabad-Pakistan. A non-thermal DC plasma jet technique was used to treat the water samples in the presence of TiO 2 catalyst. The plasma-assisted catalytic treatment introduced some oxidative species (O 3 , H 2 O 2 , HO 2 − , OH − ) in the water. These species reacted with pollutants and cause the degradation of harmful contaminants, especially dyes. The degradation of dye sample during plasma treatment was more pronounced as compared to other samples. pH, conductivity and TDS of dye containing sample decreased after catalytic plasma treatment. The degradation of organic pollutants increased due to presence of several oxidants, such as TiO 2 , ferrous ions and hydrogen peroxide. FT-IR analysis revealed the degradation of some functional groups during treatment process and conﬁrmed the e ﬀ ectiveness of the process. The residue of the treated samples was consisted of amines, amides and N-H functional groups. XRD analysis showed the presence of Alite, Ferrite, aluminate, Si, S and some heavy metals in the residue. The e ﬀ ect of plasma treatment on activity of gram-negative Escherichia coli ( E. coli ) bacteria in water was also checked. The bacterial activity was reduced by almost 50% after 2 min of plasma treatment.


Introduction
The depleting fresh water sources is a global issue. For the existence of living organisms, the water is the most vital component. The use of polluted water is causing numerous diseases. About 3.4 million people, mostly children, die every year from waterborne diseases [1][2][3]. Population of the underdeveloped countries is rising exponentially and so does the demand of clean water. Most parts of Punjab and Sindh in Pakistan have polluted and brackish ground water. Faisalabad is the second largest city in eastern province of Punjab and third most populated city of Pakistan. Faisalabad has a semi-arid four-season climate with very low to high temperatures and nearly 320 days of annual sunshine. Faisalabad has grown into a multi-industrial metropolis and distribution center due to its central location in the region. This city contributes over 20% of GDP of Punjab with annual GDP of USD 20.5 billion. Textile industry and agriculture remain its hallmark. However, this city lacks basic data related to air and water quality. Apparently, no planned environmental monitoring is being undertaken by the government in this city. absence of a catalyst and samples treated with plasma in combination with TiO2 catalyst (Z1, Z2, Z3, Z4, Z5, Z6, Z7). The flowchart of the process, adopted for plasma-assisted catalytic and non-catalytic treatment of water samples, is shown in Figure 1. Wastewater treatment plant . Figure 1. Flowchart of the plasma-assisted treatment of water samples with TiO2.

Plasma Treatment Setup
Schematic of an atmospheric pressure DC plasma treatment system is shown in Figure 2. The setup is consisted of a high-voltage DC supply, variable resistance box, Tungsten anode, copper nozzle of 2 mm orifice diameter, sample holder and gas supply valves. A total of 50 mL of a water sample was taken in a beaker and placed on the sample holder. The Tungsten anode was dipped in water sample. The copper nozzle, which also worked as a cathode, was fixed at 10 mm above the water level. The inter-electrode distance was set at 20 mm. A safety resistance of 100 kΩ was also added in the circuit to avoid breakdown in case of direct contact between electrodes. Once the circuit was complete, the argon gas was passed through plasma nozzle at a fixed flowrate of 5 LPM. A fixed

Plasma Treatment Setup
Schematic of an atmospheric pressure DC plasma treatment system is shown in Figure 2. The setup is consisted of a high-voltage DC supply, variable resistance box, Tungsten anode, copper nozzle of 2 mm orifice diameter, sample holder and gas supply valves. A total of 50 mL of a water sample was taken in a beaker and placed on the sample holder. The Tungsten anode was dipped in water sample. The copper nozzle, which also worked as a cathode, was fixed at 10 mm above the water level. The inter-electrode distance was set at 20 mm. A safety resistance of 100 kΩ was also added in the circuit to avoid breakdown in case of direct contact between electrodes. Once the circuit was complete, the argon gas was passed through plasma nozzle at a fixed flowrate of 5 LPM. A fixed voltage of 6 kV was applied across the electrodes to produce plasma jet of argon-air mixture. The plasma jet interacted with contaminated water sample and initiated some chemical reactions.
Processes 2019, 7, x FOR PEER REVIEW 4 of 15 voltage of 6 kV was applied across the electrodes to produce plasma jet of argon-air mixture. The plasma jet interacted with contaminated water sample and initiated some chemical reactions.

Figure 2.
Atmospheric pressure DC plasma treatment system.

Plasma Chemistry
Since a plasma jet was generated by discharging argon-air mixture, the possible plasma chemistry is explained in Figure 3. The plasma jet may contain several species, including neutrals, ionized particles, excited particles and electrons. Oxygen (O2), nitrogen (N2), excited argon particle (Ar*), argon ions (Ar − ), neutral argon (Ar), CO2, NO, N2O and O3 were expected in the discharge. Some other species may also be present in the plasma plume, depending on the local environment. The degradation of contaminants was anticipated due to chemical interactions of plasma species with water molecules and contaminants. The reactive species for these interactions are assumed as H2O + , H − , O3, OH − or HO −2 . The oxidation potential of these species is provided in Table 2.
The water treatment process was carried out at room temperature. Each sample was exposed individually to plasma jet for 10 min without using TiO2 catalyst. Then a similar procedure was repeated by introducing TiO2 catalyst in the reaction. Only 0.5 g of catalyst was added in the water and exposed to plasma for 10 min. Filtration of the plasma-treated water was performed to remove the catalyst and solid residue. The filtered water was analyzed to check the removal of pollutants after catalytic and noncatalytic treatment under plasma exposure. Several analyses were conducted on water samples to examine the suitability of plasma treatment for removal of pollutants from industrial effluents. These analyses include testing of pH, TDS, turbidity, conductivity, alkalinity, color, etc. No solid particles were detected in the water samples before plasma treatment. However, a white solid residue emerged in the water during plasma treatment. Th solid residue was separated from the water through centrifugation and dried in an oven for 6 h at 80 ºC. The dried residue was characterized using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) techniques.

Plasma Inactivation of Bacteria
The industrial effluents may also contain gram-negative bacteria along with heavy metals, dyes and other pollutants. Therefore, the effect of plasma treatment on inactivation of gram-negative bacteria in the water samples was also investigated. The Escherichia coli (E. Coli) bacteria was cultured and subjected to the argon plasma jet under similar conditions as set for treatment of water samples.

Plasma Chemistry
Since a plasma jet was generated by discharging argon-air mixture, the possible plasma chemistry is explained in Figure 3. The plasma jet may contain several species, including neutrals, ionized particles, excited particles and electrons. Oxygen (O 2 ), nitrogen (N 2 ), excited argon particle (Ar*), argon ions (Ar − ), neutral argon (Ar), CO 2 , NO, N 2 O and O 3 were expected in the discharge. Some other species may also be present in the plasma plume, depending on the local environment. The degradation of contaminants was anticipated due to chemical interactions of plasma species with water molecules and contaminants. The reactive species for these interactions are assumed as H 2 O + , H − , O 3 , OH − or HO −2 . The oxidation potential of these species is provided in Table 2.
The water treatment process was carried out at room temperature. Each sample was exposed individually to plasma jet for 10 min without using TiO 2 catalyst. Then a similar procedure was repeated by introducing TiO 2 catalyst in the reaction. Only 0.5 g of catalyst was added in the water and exposed to plasma for 10 min. Filtration of the plasma-treated water was performed to remove the catalyst and solid residue. The filtered water was analyzed to check the removal of pollutants after catalytic and noncatalytic treatment under plasma exposure. Several analyses were conducted on water samples to examine the suitability of plasma treatment for removal of pollutants from industrial effluents. These analyses include testing of pH, TDS, turbidity, conductivity, alkalinity, color, etc. No solid particles were detected in the water samples before plasma treatment. However, a white solid residue emerged in the water during plasma treatment. Th solid residue was separated from the water through centrifugation and dried in an oven for 6 h at 80 ºC. The dried residue was characterized using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) techniques.

Plasma Inactivation of Bacteria
The industrial effluents may also contain gram-negative bacteria along with heavy metals, dyes and other pollutants. Therefore, the effect of plasma treatment on inactivation of gram-negative bacteria in the water samples was also investigated. The Escherichia coli (E. Coli) bacteria was cultured and subjected to the argon plasma jet under similar conditions as set for treatment of water samples. The bacteria culture was exposed to plasma for 3 min under ambient conditions. The effect of plasma treatment on inactivation of bacteria was determined by counting the colony forming units (CFUs) in the sample before and after plasma exposure. treatment on inactivation of bacteria was determined by counting the colony forming units (CFUs) in the sample before and after plasma exposure.

Water Quality Parameters
Most of the samples exhibited a slight increase in pH value during plasma treatment, as shown in Table 3. An increase in pH of water is related to increase of OH radicals during plasma treatment. A change in pH of sample depends on concentration of OH radicals in the sample. In this experiment, pH of X1, X2, X3, X5, X6 and X7 samples increased after plasma treatment. However, pH of dye containing sample (X4) decreased from 12.2 to 12 after plasma treatment in the absence of catalyst. In the presence of catalyst, pH of sample declined twofold after 10 min of plasma treatment. Similar results were reported by Sugiarto et al. [15]. A decrease in pH of X4 is attributed to the alkaline nature of the sample [16]. As shown in Table 3, the electrical conductivity of some of the samples increased after plasma treatment, while other samples exhibited a decrease in electrical conductivity. An increase in conductivity is attributed to the formation of by-products in the sample during plasma treatment while decrease in conductivity was due to conversion of soluble inorganic salts to insoluble ones. This change in electrical conductivity also depends on the nature of intermediates formed during plasma processing of the water samples [17].
Both catalytic and noncatalytic plasma treatments did not show notable influence on total dissolved solid (TDS) except for dye sample (X4). TDS value of X4 decreased by 140 points after simple plasma treatment and 190 points after catalytic plasma treatment. Similarly, some samples showed slight increase in hardness on plasma treatment. The degradation efficiency of organic pollutants increased in the presence of several oxidants, such as TiO2, ferrous ion and hydrogen peroxide [18].
The inorganic particles like sulfates and phosphates were also present in the samples. A change in sulfate and phosphate contents of plasma-treated samples is attributed to the by-products obtained during plasma treatment. The presence of sulfate ions in solution also caused a decrease in percentage degradation because these ions could react with OH radicals in solution and result in their depletion. According to Ghezzr et al. [19], degradation of inorganic compounds starts after 20 min of plasma treatment [20].

Water Quality Parameters
Most of the samples exhibited a slight increase in pH value during plasma treatment, as shown in Table 3. An increase in pH of water is related to increase of OH radicals during plasma treatment. A change in pH of sample depends on concentration of OH radicals in the sample. In this experiment, pH of X 1 , X 2 , X 3 , X 5 , X 6 and X 7 samples increased after plasma treatment. However, pH of dye containing sample (X 4 ) decreased from 12.2 to 12 after plasma treatment in the absence of catalyst. In the presence of catalyst, pH of sample declined twofold after 10 min of plasma treatment. Similar results were reported by Sugiarto et al. [15]. A decrease in pH of X 4 is attributed to the alkaline nature of the sample [16]. As shown in Table 3, the electrical conductivity of some of the samples increased after plasma treatment, while other samples exhibited a decrease in electrical conductivity. An increase in conductivity is attributed to the formation of by-products in the sample during plasma treatment while decrease in conductivity was due to conversion of soluble inorganic salts to insoluble ones. This change in electrical conductivity also depends on the nature of intermediates formed during plasma processing of the water samples [17].
Both catalytic and noncatalytic plasma treatments did not show notable influence on total dissolved solid (TDS) except for dye sample (X 4 ). TDS value of X 4 decreased by 140 points after simple plasma treatment and 190 points after catalytic plasma treatment. Similarly, some samples showed slight increase in hardness on plasma treatment. The degradation efficiency of organic pollutants increased in the presence of several oxidants, such as TiO 2 , ferrous ion and hydrogen peroxide [18].
The inorganic particles like sulfates and phosphates were also present in the samples. A change in sulfate and phosphate contents of plasma-treated samples is attributed to the by-products obtained during plasma treatment. The presence of sulfate ions in solution also caused a decrease in percentage degradation because these ions could react with OH radicals in solution and result in their depletion.
Hu et al. [21] reported photocatalytic degradation of two azo dyes called Procion Red MX-5B (MX-5B) and Cationic Blue X-GRL (CBX). They observed the effect of inorganic ions on the photocatalyst activity of TiO 2 and its role in degradation of dyes. Both dyes reacted differently with different pH ranges in the presence of a catalyst. The presence of inorganic ions (sulfates and phosphates) in the solution significantly influenced the degradation of dyes. Ghezzar et al. [19] degraded two textile wastewater samples having different pH values. They used gliding arc discharge technique to degrade the samples with and without using TiO 2 catalyst. The effect of catalyst amount and plasma treatment time on degradation of wastewater was investigated. The degradation activity of TiO 2 depends on pH, catalyst amount and treatment time. In the presented work, catalytic did not shown significant effect on removal of inorganic substances as the catalytic activity is pH dependent and almost all the samples were alkaline in nature. pH dependence may explain why the organic compounds are degraded in acid medium but not in basic solution [22].
Different water quality parameters, such as pH, TDS, hardness, conductivity, sulfates and phosphates for the tested samples are given in Table 3. Most of the samples did not show any noticeable change in quality parameters after plasma treatment. The dye containing samples (X 4 , Y 4 , Z 4 ) showed appreciable improvement in quality parameters. The acceptable ranges of standard water quality parameters are shown in Table 4.  Table 4. Acceptable ranges of standard water quality parameters. The hardness testing of the reported samples produced random results. Hardness is basically referred to the amount of calcium and magnesium in water. It causes harmful impact on human health [23]. In this study, no predictable trend of hardness was observed. Some samples exhibited slight increase in hardness while others showed slightly decreasing trend. However, in the presence of the catalyst, most of the samples underwent a slight decrease in hardness. The possible reason for having least effect of plasma on hardness is the treatment of samples under constant plasma pressure, applied voltage and exposure time. Yang et al. [24] revealed that water hardness is mainly due to presence of CaCO 3 , Na 2 CO 3 and CaCl 2 . To remove such water hardening particles, they adopted a pulsed spark discharge technique. The experiments were performed with different gas flowrates (200, 300 and 400 mL/min). Hardness was decreased with an increase in gas flowrate.

Identification of Heavy Metals
As shown in Figures 4-8, some heavy metals (Ni, Pb, Cd, Cu and Cr) were detected in the tested samples. The concentration of heavy metals in plasma-treated and untreated samples were examined by using atomic absorption spectrophotometer. This technique is used to identify the concentration of elements present in the sample. In dye containing sample, significant removal of metals was observed during plasma treatment. The notable removal shows the effectiveness of the treatment process, especially for dye containing water ( Figure 4). The high degradation of dye in samples is attributed to its alkaline nature (pH 12) [25]. The removal of metals from the sample depends on the pH of the sample. Ke et al. [25] reported the highest removal of Cr (VI) from samples of high pH due to presence of more reducing species in the sample. As TiO 2 is more effective for organic compounds, some of the metals were removed from the water in the presence of catalyst while others were not. The hardness testing of the reported samples produced random results. Hardness is basically referred to the amount of calcium and magnesium in water. It causes harmful impact on human health [23]. In this study, no predictable trend of hardness was observed. Some samples exhibited slight increase in hardness while others showed slightly decreasing trend. However, in the presence of the catalyst, most of the samples underwent a slight decrease in hardness. The possible reason for having least effect of plasma on hardness is the treatment of samples under constant plasma pressure, applied voltage and exposure time. Yang et al. [24] revealed that water hardness is mainly due to presence of CaCO3, Na2CO3 and CaCl2. To remove such water hardening particles, they adopted a pulsed spark discharge technique. The experiments were performed with different gas flowrates (200, 300 and 400 mL/min). Hardness was decreased with an increase in gas flowrate.

Identification of Heavy Metals
As shown in Figures 4-8, some heavy metals (Ni, Pb, Cd, Cu and Cr) were detected in the tested samples. The concentration of heavy metals in plasma-treated and untreated samples were examined by using atomic absorption spectrophotometer. This technique is used to identify the concentration of elements present in the sample. In dye containing sample, significant removal of metals was observed during plasma treatment. The notable removal shows the effectiveness of the treatment process, especially for dye containing water ( Figure 4). The high degradation of dye in samples is attributed to its alkaline nature (pH 12) [25]. The removal of metals from the sample depends on the pH of the sample. Ke et al. [25] reported the highest removal of Cr (VI) from samples of high pH due to presence of more reducing species in the sample. As TiO2 is more effective for organic compounds, some of the metals were removed from the water in the presence of catalyst while others were not. A comparison of heavy metals can be discussed based on concentration of metals. The concentration of some metals increased while others decreased after catalytic and noncatalytic plasma treatments. Due to the formation of by-products in the sample during plasma treatment, the increment levels of metals occurred through catalytic activity. As seen in Figure 5, concentration of Cu in all samples increased with plasma treatment except X4 sample. As for Pb, it was found in most of the untreated water samples. Pb was removed from almost all water samples after plasma treatment. Upon plasma treatment, as shown in Figure 6, Pb was completely absent in dye containing water sample. Almost similar results were obtained for Ni, Cr and Cd metals in plasma-treated samples. A comparison of heavy metals can be discussed based on concentration of metals. The concentration of some metals increased while others decreased after catalytic and noncatalytic plasma treatments. Due to the formation of by-products in the sample during plasma treatment, the increment levels of metals occurred through catalytic activity. As seen in Figure 5, concentration of Cu in all samples increased with plasma treatment except X 4 sample. As for Pb, it was found in most of the untreated water samples. Pb was removed from almost all water samples after plasma treatment. Upon plasma treatment, as shown in Figure 6, Pb was completely absent in dye containing water sample. Almost similar results were obtained for Ni, Cr and Cd metals in plasma-treated samples.  Icopini et al. [26] tested wastewater samples of different pH values for identification of Cr. It was observed that Cr containing solution will be either neutral or positively charged for lower pH values [26]. Cserfalvi et al. [27] used a glow discharge technique to figure out the presence of metals in the solution. The electron temperature in the glow discharge was measured about 5000 K. They used an advanced electrolyte-cathode discharge spectrometry technique for identification of metals, like Ni, Cu, Pb, Zn, Cd and Mn in water samples. Each metal had a specific peak intensity value and concentration curve, depending on pH and hydrogen ion concentration of the tested solution. In this work, the simple plasma treatment did not significantly promote the removal of heavy metals from the water samples. However, catalytic plasma treatment significantly suppressed Ni concentration. As shown in Figure 7, all untreated and plasma-treated samples measured Ni though, in the presence of a catalyst, it was almost absent from the sample treated with plasma. Cd was present in untreated tap water and the sample collected from wastewater treatment plant. The simple plasma and catalytic plasma treatments did not affect Cd in X2 sample, while Cd was not detected in other plasma-treated samples (Figure 8).  Icopini et al. [26] tested wastewater samples of different pH values for identification of Cr. It was observed that Cr containing solution will be either neutral or positively charged for lower pH values [26]. Cserfalvi et al. [27] used a glow discharge technique to figure out the presence of metals in the solution. The electron temperature in the glow discharge was measured about 5000 K. They used an advanced electrolyte-cathode discharge spectrometry technique for identification of metals, like Ni, Cu, Pb, Zn, Cd and Mn in water samples. Each metal had a specific peak intensity value and concentration curve, depending on pH and hydrogen ion concentration of the tested solution. In this work, the simple plasma treatment did not significantly promote the removal of heavy metals from the water samples. However, catalytic plasma treatment significantly suppressed Ni concentration. As shown in Figure 7, all untreated and plasma-treated samples measured Ni though, in the presence of a catalyst, it was almost absent from the sample treated with plasma. Cd was present in untreated tap water and the sample collected from wastewater treatment plant. The simple plasma and catalytic plasma treatments did not affect Cd in X2 sample, while Cd was not detected in other plasma-treated samples (Figure 8). Icopini et al. [26] tested wastewater samples of different pH values for identification of Cr. It was observed that Cr containing solution will be either neutral or positively charged for lower pH values [26]. Cserfalvi et al. [27] used a glow discharge technique to figure out the presence of metals in the solution. The electron temperature in the glow discharge was measured about 5000 K. They used an advanced electrolyte-cathode discharge spectrometry technique for identification of metals, like Ni, Cu, Pb, Zn, Cd and Mn in water samples. Each metal had a specific peak intensity value and concentration curve, depending on pH and hydrogen ion concentration of the tested solution. In this work, the simple plasma treatment did not significantly promote the removal of heavy metals from the water samples. However, catalytic plasma treatment significantly suppressed Ni concentration. As shown in Figure 7, all untreated and plasma-treated samples measured Ni though, in the presence of a catalyst, it was almost absent from the sample treated with plasma. Cd was present in untreated tap water and the sample collected from wastewater treatment plant. The simple plasma and catalytic plasma treatments did not affect Cd in X 2 sample, while Cd was not detected in other plasma-treated samples (Figure 8).

FT-IR and XRD Analysis of Residue
After sampling, the water samples were left undisturbed for 24 h. Some solid particles settled down at the bottom of container having industrial wastewater (X5). The solid residue was separated from the wastewater through centrifugation. This water sample was given simple plasma and catalytic plasma treatment in separate runs. As shown in Figure 9, some solid residues again settled down at the bottom of beaker during plasma treatment, which were separated from the water through centrifugation. The solid residues of untreated (X5), plasma-treated (Y5) and catalytic plasmatreated (Z5) samples were dried in an oven for 6 h. These residues were analyzed through FT-IR and XRD techniques, FT-IR patterns of the residue are shown in Figure 10. The degradation of some functional groups during treatment process confirmed the effectiveness of plasma treatment process. The residue contained hydroxyl, amine, amides, ester, ether, carboxylic acids and anhydrides. In the range of 3320-3520 cm −1 , aromatic amines, primary amines and amides with N-H stretching were observed in the sample. The broad band at ~3482 cm −1 was simply due to interaction of hydroxyl groups in water and the band near 1630 cm −1 comes from the scissoring of water molecules. C-O-C

FT-IR and XRD Analysis of Residue
After sampling, the water samples were left undisturbed for 24 h. Some solid particles settled down at the bottom of container having industrial wastewater (X5). The solid residue was separated from the wastewater through centrifugation. This water sample was given simple plasma and catalytic plasma treatment in separate runs. As shown in Figure 9, some solid residues again settled down at the bottom of beaker during plasma treatment, which were separated from the water through centrifugation. The solid residues of untreated (X5), plasma-treated (Y5) and catalytic plasmatreated (Z5) samples were dried in an oven for 6 h. These residues were analyzed through FT-IR and XRD techniques, FT-IR patterns of the residue are shown in Figure 10. The degradation of some functional groups during treatment process confirmed the effectiveness of plasma treatment process. The residue contained hydroxyl, amine, amides, ester, ether, carboxylic acids and anhydrides. In the range of 3320-3520 cm −1 , aromatic amines, primary amines and amides with N-H stretching were observed in the sample. The broad band at ~3482 cm −1 was simply due to interaction of hydroxyl groups in water and the band near 1630 cm −1 comes from the scissoring of water molecules. C-O-C

FT-IR and XRD Analysis of Residue
After sampling, the water samples were left undisturbed for 24 h. Some solid particles settled down at the bottom of container having industrial wastewater (X 5 ). The solid residue was separated from the wastewater through centrifugation. This water sample was given simple plasma and catalytic plasma treatment in separate runs. As shown in Figure 9, some solid residues again settled down at the bottom of beaker during plasma treatment, which were separated from the water through centrifugation. The solid residues of untreated (X 5 ), plasma-treated (Y 5 ) and catalytic plasma-treated (Z 5 ) samples were dried in an oven for 6 h. These residues were analyzed through FT-IR and XRD techniques, FT-IR patterns of the residue are shown in Figure 10. The degradation of some functional groups during treatment process confirmed the effectiveness of plasma treatment process. The residue contained hydroxyl, amine, amides, ester, ether, carboxylic acids and anhydrides. In the range of 3320-3520 cm −1 , aromatic amines, primary amines and amides with N-H stretching were observed in the sample. The broad band at~3482 cm −1 was simply due to interaction of hydroxyl groups in water and the band near 1630 cm −1 comes from the scissoring of water molecules. C-O-C linkage in ether was observed in the range of 1070-1240 cm −1 . In the range of 1140-1200 cm −1 , sulfates (S=O) had SO 2 symmetric stretching, while the C-C=O group in ketones was present in the range of 510-560 cm −1 . Similar results were reported by Tichonovas et al. [16] for plasma-treated industrial wastewater. They treated contaminated water with dielectric barrier discharge plasma under atmospheric conditions. The functional groups, found in their investigations, include amines, amides, nitrates and carboxylic acids. Parshetti et al. [28] used Rhizobium radiobacter pathogen for degradation of methyl violet and some other industrial dyes, such as red HE7B, yellow 4G, blue 2B, navy blue HE22, red M5B and red HE3B. Adsorption of methyl violet and removal of some organic contaminants were observed in the presence of poly (acrylamide-co-acrylic acid) hydrogels. Solpan et al. [29] used Poly(AAm-co-AAc) as an absorbent for dyes and other contaminants in the solution. In the range of 1140-1200 cm −1 , sulfates (S=O) had SO2 symmetric stretching, while the C-C=O group in ketones was present in the range of 510-560 cm −1 . Similar results were reported by Tichonovas et al. [16] for plasma-treated industrial wastewater. They treated contaminated water with dielectric barrier discharge plasma under atmospheric conditions. The functional groups, found in their investigations, include amines, amides, nitrates and carboxylic acids. Parshetti et al. [28] used Rhizobium radiobacter pathogen for degradation of methyl violet and some other industrial dyes, such as red HE7B, yellow 4G, blue 2B, navy blue HE22, red M5B and red HE3B. Adsorption of methyl violet and removal of some organic contaminants were observed in the presence of poly (acrylamide-co-acrylic acid) hydrogels. Solpan et al. [29] used Poly(AAm-co-AAc) as an absorbent for dyes and other contaminants in the solution.    In the range of 1140-1200 cm −1 , sulfates (S=O) had SO2 symmetric stretching, while the C-C=O group in ketones was present in the range of 510-560 cm −1 . Similar results were reported by Tichonovas et al. [16] for plasma-treated industrial wastewater. They treated contaminated water with dielectric barrier discharge plasma under atmospheric conditions. The functional groups, found in their investigations, include amines, amides, nitrates and carboxylic acids. Parshetti et al. [28] used Rhizobium radiobacter pathogen for degradation of methyl violet and some other industrial dyes, such as red HE7B, yellow 4G, blue 2B, navy blue HE22, red M5B and red HE3B. Adsorption of methyl violet and removal of some organic contaminants were observed in the presence of poly (acrylamide-co-acrylic acid) hydrogels. Solpan et al. [29] used Poly(AAm-co-AAc) as an absorbent for dyes and other contaminants in the solution.    The plasma produced oxygen under plasma jet exposure and that was already present in water reacted with metals to form metal oxides. The residue of plasma treatment and catalytic plasma treatment was characterized by generating XRD patterns. The heavy metals in wastewater comes from both natural and man-made sources. The major natural sources of heavy metals are volcanic activities, soil erosion, urban runoffs and aerosols. The man-made sources are electroplating, metal finishing, textile dying, mining operations, leader industry, glass industry, metallurgical industry, automobile manufacturing, washing and direct industrial wastes. Faisalabad is a major industrial and distribution center and anchor of all these industries. The toxic metals from industry releases into wastewater through rinsing, spillage and dumping. The cleaning of bath tanks and chemical containers also produces substantial quantities of wet sludge of toxic metals. Sharma et al. [30] investigated the presence of heavy metals in industrial wastewater. They reported several heavy metals in the industrial wastewater collected from different parts of India. They used metallic nanoparticles for the removal of heavy metals. In this study, TiO 2 nanoparticles were used to remove the heavy metals under plasma exposure. XRD patterns of solid residue of plasma-treated water samples are shown in Figure 11. The atomic oxygen and oxygen radicals converted some metals into their oxides [30,31]. Both plasma-treated and catalyst/plasma-treated samples contained almost same metals and oxides. The only difference was the presence of TiO 2 , which was used as a catalyst in the second trial. XRD peaks of TiO 2 are identified as anatase and rutile phases.
activities, soil erosion, urban runoffs and aerosols. The man-made sources are electroplating, metal finishing, textile dying, mining operations, leader industry, glass industry, metallurgical industry, automobile manufacturing, washing and direct industrial wastes. Faisalabad is a major industrial and distribution center and anchor of all these industries. The toxic metals from industry releases into wastewater through rinsing, spillage and dumping. The cleaning of bath tanks and chemical containers also produces substantial quantities of wet sludge of toxic metals. Sharma et al. [30] investigated the presence of heavy metals in industrial wastewater. They reported several heavy metals in the industrial wastewater collected from different parts of India. They used metallic nanoparticles for the removal of heavy metals. In this study, TiO2 nanoparticles were used to remove the heavy metals under plasma exposure. XRD patterns of solid residue of plasma-treated water samples are shown in Figure 11. The atomic oxygen and oxygen radicals converted some metals into their oxides [30,31]. Both plasma-treated and catalyst/plasma-treated samples contained almost same metals and oxides. The only difference was the presence of TiO2, which was used as a catalyst in the second trial. XRD peaks of TiO2 are identified as anatase and rutile phases. XRD

Angle (2θ)
Residue after catalyst/plasma treatment Figure 11. XRD patterns of the solid residue of plasma-treated and catalyst/plasma-treated industrial wastewater.

Effect of Plasma Treatment on Bacteria Inactivation
In untreated and inadequately treated waters, various forms of bacteria can be present. Examining water for all types of bacteria is not feasible, but testing for coliform bacteria is a relatively

Effect of Plasma Treatment on Bacteria Inactivation
In untreated and inadequately treated waters, various forms of bacteria can be present. Examining water for all types of bacteria is not feasible, but testing for coliform bacteria is a relatively simpler way of accessing the water quality. Coliforms are the naturally found bacteria in the environment. The presence of coliform bacteria in water is a sign of presence of several other dangerous bacteria. E. Coli is a gram-negative coliform and its presence in water causes short-term health problems by putting the health of elderly people, infants and those having weak immune systems at risk. Since most of the wastewaters contain gram-negative bacteria, the effect of plasma treatment on inactivation of E. Coli (gram-negative) was investigated. The bacteria culture was exposed to DC plasma jet for 2 min. The pre-and post-plasma treatment bacteria colony-forming units (CFUs) were counted using a digital counter. The binary converted photographs of untreated and plasma-treated bacterial cultures are shown in Figure 12. The change in CFU count of bacteria with plasma treatment time is shown in Figure 13. simpler way of accessing the water quality. Coliforms are the naturally found bacteria in the environment. The presence of coliform bacteria in water is a sign of presence of several other dangerous bacteria. E. Coli is a gram-negative coliform and its presence in water causes short-term health problems by putting the health of elderly people, infants and those having weak immune systems at risk. Since most of the wastewaters contain gram-negative bacteria, the effect of plasma treatment on inactivation of E. Coli (gram-negative) was investigated. The bacteria culture was exposed to DC plasma jet for 2 min. The pre-and post-plasma treatment bacteria colony-forming units (CFUs) were counted using a digital counter. The binary converted photographs of untreated and plasma-treated bacterial cultures are shown in Figure 12. The change in CFU count of bacteria with plasma treatment time is shown in Figure 13. CFU counts were reduced by 50% after plasma treatment time of 2 min. Hereinafter, plasma treatment did not show significant effect on bacterial culture. A similar bacteria inactivation trend was observed for catalytic plasma treatment. It reveals that TiO2 nanoparticles are not very effective for antibacterial treatment of contaminated water. Raza et al. [31] used chromium oxide nanoparticles for killing micro-organisms, such as E. coli and Pseudomonas aeruginosa. Chromium chloride was used as precursor for synthesis of nanoparticles. Vo et al. [32] produced controlled size triangular nanoparticles of silver. They studied the effect of shape on antibacterial activity of these silver nanoparticles. However, the use of such materials for bacterial inactivation is itself an expensive process, which needs a lot of post processing as well. On the other hand, plasma treatment is a simple, nontoxic and single-step process for antibacterial treatments. Additionally, no post-treatment processing of the sample is need. Figure 12. Scattering configuration of CFUs of E. Coli before (a) and after (b) plasma treatment. Only the plasma-exposed area is shown in the photograph. Figure 12. Scattering configuration of CFUs of E. Coli before (a) and after (b) plasma treatment. Only the plasma-exposed area is shown in the photograph. Several authors have confirmed the effectiveness of plasmas as pathogens disinfectant [12][13][14][15][16]. Several factors play a role in plasma inactivation of bacteria. Most atmospheric plasma jets produce UV radiations in the range of 200 to 300 nm. These radiations weaken the bacteria cell wall by transferring the energy of the cell membrane. Since a argon-air mixture was used as a precursor gas for production of plasma jet, the possibility of reactive oxygen species being present in plasma also ruptured the bacteria cell. The electrically-charged species in the plasma jet accumulated on the