Table 1.

Effect of different cold plasma discharges on various pollutants present in wastewater

S. No.	Type of cold plasma discharge used	Treatment (dose and time)	Source of wastewater	Target pollutant	Other properties of treated wastewater	Observed effects	Reference
1.	High voltage DC pulsed discharge NTP reactor	Sample A (300, 500, 900 pps for 0.2s) Sample B (500 pps for 0.2 s)	Viscous oil fields	● Silica content	● Hardness ● pH ● Electrical conductivity	● Treatment showed reduction of silica content by 50 % and 43 % at 500 pps in sample A and B, respectively. ● After treatment hardness was reduced by 57 % at 900pps and 53 % at 500 pps in sample A and B, respectively. ● pH of sample A and B was slightly reduced by 3 % and 2 % in sample A and B. ● An increment of electrical conductivity of around 6 % and 19 % at 500 pps was observed in sample A and B.	Wang et al., (2015)
2.	GAD falling film reactor coupled with TiO2	9000 V for 60, 70, 120, 140 180 min	The tested chemical was dissolved in distilled water	● Acid Green 25 (AG25) Anthraquinone dye	● Total organic carbon (TOC)	● After exposure to treatment for 60 mins, significant reduction by 60% and 94% was observed in GAD and GAD-TiO2 treated samples and in GAD process 94 % reduction was achieved after 180 mins. ● After treating for 180 mins, significant degradation of about 59 % and 85 % in TOC was observed in GAD and GAD-TiO2 treated samples.	Saïm et al. (2015)
3.	PCDP coupled with natural SPs	24.1 kV at 75 Hz for 0, 10, 20, 30, 40, 50, 60 min with BS, LS & RS	Purchased TCH was dissolved in water	● Tetracycline Hydrochloride (TCH)	● Total organic carbon (TOC)	● On treating 60 mins, the removal efficacy of TCH was significantly increased by 46.43 %, 36.17 % & 22.79 % in RS, LS & BS coupled with corona discharge. ● With increase in treatment time, reduction in TOC was observed indicating TCH might be broken down into small inorganic molecules.	Wang et al. 2018
4.	APPJ, using He gas	4.8 kV for 40-50 & ≥ 40 mins at 2.5 and 10 L/min flow rate of He	Aqueous solution of the tested chemical was prepared	● Methylene Blue dye	_	● Initially, the colour of solution was dark blue. But after treatment for 40-50 mins at 2.5L/min flow rate it turned into light blue. ● Furthermore, at ≥ 40 mins treatment time with 10L/min flow rate there was complete decolourization of MB solution.	Abdel-Fattah 2019
5.	Gas phase DBD	7 kHz, 7 kV for 60, 80, 100, 120 min	Coke plant in Dalian, China	● Total phenols ● PAHs (like naphthalenol, dimethyl phthalate, benzoquinone) ● NH3-N	● COD ● BOD5/COD	● With 60 and 80 mins treatment time, removal efficacy of low phenols and high phenols concentration reached around 100 %, respectively. ● Similarly, complete removal of all PAHs compounds was also observed. ● Likewise, significant removal of around 21 % was observed in NH3-N and 70 % in COD with 120 mins treatment time. ● BOD5/COD showed an increment of around 0.52 from 0.14 after 100 mins treatment time. Thus, showed significant improvement in biodegradability of wastewater.	Duan et al. (2015)
6.	DBD coupled with Fe-based zeolite	20.0 kV, 14.5 kHz, 2.0 g (Fe-catalyst dosage) for 20 min at 25°C	Ammonia nitrogen and phenol wastewater was prepared	● Ammonia nitrogen ● Phenols	● pH ● Conductivity	● Initially, concentration of ammonia nitrogen was 100 mg/L but after treatment its removal rate reached up to 75.11 %. ● Similarly, the initial concentration of phenols was 20 mg/L but after treatment their removal rate reached up to 56.67 %. ● Slight increase in pH and conductivity (up to 1.981 mS/cm) was also observed after treatment.	Wu et al. (2020)
7.	Pilot-scale gas phase PCD	0.5 kWhm-3 and 1 kWhm-3	Raw sewage from Etelä-Karjala central hospital and biologically treated wastewater from Rinnekoti foundation	● Pharmaceuticals (32 compounds)	● Colour ● Turbidity ● Conductivity	● After treatment, pharmaceuticals content (excepting biodegradable caffeine) in raw sewage was reduced by 87 % at 1 kWhm-3 while this reduction was 100 % in biologically treated wastewater at 0.5 kWhm-3. ● Further, significant reduction of about 58 % and 47 % was observed in colour and turbidity. ● Slight increase in conductivity of wastewater was observed after treatment.	Ajo et al. (2018)
8.	APPJ (zero air, nitrogen & argon gas)	16 to 20 kV at 50 Hz for 0, 10, 20, 30, 40 min	The tested chemical was dissolved in Milli-Q-water	● Methylene Blue dye	● pH ● Conductance	● Argon plasma showed the highest degradation of MB. It was degraded by 100 % for 20 ppm and 99 %, 97 % & 96 % for 30, 40 & 50 ppm respectively while, in case of zero air & nitrogen plasma degradation of MB was 88 % & 72 % for 50 ppm, respectively. ● pH got reduced by 3.2 in argon plasma after treatment for 40 mins. ● Conductance was highest (from 2.9 to 1700 μS/cm) in case of zero air plasma.	Chandana et al. 2015
9.	NTAPP coupled with Cu-CeO2 NPs	31 kV for 30 mins followed by 20mg addition of Cu-CeO2 NPs & again plasma treated for 5,10,15, 20, 25 mins at 31 kV	The aqueous solution of tested chemical was prepared	● Reactive Black-5(RB-5) dye	● pH ● Electrical conductance (EC) ● Total organic carbon	● Treatment for 25 mins, maximum degradation of 77.4 % was observed in RB-5 while this degradation was only 38 % after 30 mins treatment time when plasma alone was used. ● Initial pH of solution was 7.67 which got reduced by 4.9 after treatment. Hence, reduction of around 36 % was observed, while the EC showed opposite behaviour. ● Similarly, after treatment for 25 mins, a maximum degradation of 55.36 % was observed in TOC while this degradation was only 7.52 % after 30 mins treatment time when plasma alone was used.	Pandiyaraj et al. 2021
10.	NTAPP coupled with Cu-CeO2 NPs	31 kV for 30 mins followed by 20 mg addition of Cu-CeO2 NPs & again plasma treated for 10, 20, 30 min at 35 kV	Junior textile dying, Tirupur, India	● Colour	● pH ● Electrical conductance (EC) ● Total organic carbon (TOC)	● Initial colour of the received effluent was black. But after treatment for 30 mins with plasma+Cu-CeO2 NPs, the solution turns colourless. ● pH of solution got reduced by 7.82 after treatment. ● An increase in EC from 3.67 to 5.16 μS/cm was observed. ● Furthermore, after treatment for 30 mins with plasma+Cu-CeO2 NPs a reduction of 48.2 % was observed in TOC.	Pandiyaraj et al. 2021
11.	Pulsed corona discharge	Delivered energy at 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 kWh/m3	WWTP of Guangdong Shaoguan steel company	● Biodegradability (BOD5/COD) ● Thiocyanate	● pH ● Electrical conductivity	● Biodegradability of wastewater increased by 0.43 after treatment at 42 kWh/m3. ● Thiocyanate concentration of received effluent got reduced by 86mg/L after treatment at 42 kWh/m3. Hence, a reduction of about 75 % was observed. ● Decrease in pH of 5.5 was observed after treatment at 50 kWh/m3. ● Slight increment from 570 to 600 μS/cm was observed in EC of treated samples.	Liu et al. 2018b
12.	GAD coupled with TiO2 catalyst	9000 V for 0, 30, 60, 90, 120, 150, 180 min	SORTEX plant Two samples were taken (one before treatment in purifying unit & 2nd was locally treated)	● Colour ● Turbidity ● COD	● Biodegradability (BOD5/COD) ● pH	● Change in colour up to colourless state was observed in both samples after 30- & 20-mins but the decolourization process was fast in sample 2 (20 mins). ● In sample 1, turbidity got reduced by 83.2 % after 180 mins when only GAD was used while this reduction was up to 94 % in presence of TiO2. Similarly, in sample 2 it was reduced by 81 % and 94.5 % by GAD and GAD TiO2 treatment, respectively. ● Likewise, COD of sample 1 & 2 got reduced by 94.6 % & 96 % after 180 mins in presence of catalyst along with GAD. ● Decrease in pH was observed in both samples after treatment. After 60 mins, pH of sample 1 & 2 was 0.80 & 1.5, respectively. ● Biodegradability of both samples was improved after 30 mins treatment time.	Ghezzar et al. 2009

PAHsPoly-cyclic aromatic hydrocarbons; NH₃-N ammoniacal nitrogen; BS black soil of Jilin; LS Loess soil of Shaanxi; RS red soil of Hunan; APPJ atmospheric pressure plasma jet; He helium; NTPnon-thermal plasma; DC direct current; GAD gliding arc discharge; TiO₂ titanium dioxide; PCDC pulsed corona discharge plasma; SPs Soil particles; Fe iron; NETAPPnon-thermal atmospheric pressure plasma; Cu-CeO₂NPscopper-doped cerium oxide nanoparticles; WWTP wastewater treatment plant; COD chemical oxygen demand; BOD₅/COD biodegradability