Table 2.

Effect of different cold plasma discharges on various pathogenic micro-organisms including viruses present in wastewater

S. No.	Type of cold plasma discharge used	Treatment (dose and time)	Source of wastewater	Target pathogenic microbe or virus	Other properties of treated wastewater	Observed effects	References
1.	DBD-ACP system	60, 70, 80 kV for 0,1,2,5 min	Dairy and meat industry	● E. coli ● E. faecalis ● Clostridium perfringens ● Vegetative cells and spores of Bacillus megaterium	● Toxicity	● Significant reduction by 16 %, 30 % and 49 % was observed in E. coli at 60, 70 and 80 kV with 2 mins respectively. ● Similarly, C. perfringens was also reduced by 22 %, 37 % and 29 % at 60, 70 and 80 kV with 2 mins treatment time, respectively. ● Furthermore, with 5 mins treatment time reduction was up to undetectable levels at all three-voltage levels in E. coli and C. perfringens. ● Likewise, significant reduction of around 24% and 42 % was also observed in E. faecalis at 70 and 80 kV with 2 mins, respectively. However, with 5 mins reduction was up to undetectable levels at 70 and 80 kV while, at 60 kV it got reduced by 53 %. ● With 5 mins treatment time, vegetative cells of B. megaterium were completely inactivated while, population of spores was decreased by ±1.9 log10 CFUml-1. ● Furthermore, plasma treatment limited the toxic effects but it was dependent on treatment time and concentration of treated effluents.	Patange et al. (2018)
2.	FE-DBD cold plasma system	10 kHz, 18 kV for 10 min	WWTP of a Greek municipality	● Salmonella spp. ● Coliforms ● Escherichia coli		● 100% removal of all Salmonella spp. after a treatment for 10 mins. ● Likewise, Coliforms and E. coli load was less than 40 CFUs g-1 after treatment	Svarnas et al. (2020)
3.	Multi-hole DBD	15 kV at 25 kHz for 20min	Seaweed processing plant	● Escherichia coli	● BOD ● COD ● Turbidity ● pH ● Colour ● Conductivity	● E. coli population was significantly reduced by 99.99 % after treatment. ● BOD and COD of wastewater got reduced by 18.6 mgL-1 and 23.9 mgL-1, respectively. ● Turbidity of wastewater was reduced by 5.8 NTU, respectively. Hence, a reduction of around 59% was observed. ● Slight increase in pH by 8.51, i.e. around 22% was observed. ● Red colour of contaminated wastewater disappeared after being treated due to oxidation of organic pollutants. ● Minimal changes in conductivity were observed after treatment.	Ma et al. (2020)
4.	Atmospheric pressure NTP reactor	2 kV, 4 kV, 6 kV for 20 mins followed by spreading after every 5 min	The strains were incorporated artificially using distilled water	● Gram negative E. coli ● Gram positive E. faecalis	● pH ● Electrical conductivity	● Concentration of E. coli was reduced by about 100 % after 15 mins treatment time at 6 kV. ● Similarly, concentration of E. faecalis was also reduced by 100 % at 4 kV & 6 kV with treatment time of 10 & 5 mins, respectively. ● Decrease in pH (neutral to acidic) and increase in electrical conductivity was observed.	Murugesan et al. (2020)
5.	Multi hole DBD	2 kW at 20 kHz for 5 min	Aqua pathogens were incorporated in artificial saline water	● Vibrio harveyi ● Vibrio ichthyoenteri ● Vibrio damsela ● Streptococcus parauberis ● Edwardsiella tarda	● E. coli	● Initial concentration of all five aqua pathogens was 2.8×108 cells/ml. After one day of treatment, it was reduced by log(N/N0) -3.8, -7, -7.8, -6.4 & -4 in Vibrio harveyi, Vibrio ichthyoenteri, Vibrio damsela, Streptococcus parauberis, Edwardsiella tarda, respectively. ● Initially, the population of E. coli was 108 CFU/ml. After 5 mins treatment time it significantly reduced by -4.5 log (N/N0).	Hong et al. (2019)
6.	DBD plasma reactor	5–30 kHz, 0–30 kV for 10 s, 30 s, 60s, 120 s, 240 s	Beijing water treatment plant	● E. coli ● S. aureus ● Bacillus subtilis	● pH ● Natural organic matter	● Initial concentration of E. coli, S. aureus, B. subtilis was 1.0×107 CFU/ml, 5.7×107CFU/ml and 7.5×107 CFU/ml, respectively. After treatment for 30s, the log inactivation ratio of E. coli and B. subtilis was 7.0 and 1.1 log, while in S. aureus it was 7.8 log after 10s. ● Decrease in natural organic matter and pH was also observed after treatment.	Zhang et al. (2016)
7.	DC air liquid discharge plasma	10 kV for 0, 5, 10, 15, 20 min	Single colony of E. coli and S. aureus were overnight cultured in fresh sterile LB and TSB and their 4ml was taken for treatment	● E. coli ● S. aureus	● Metabolic activity of cells	● Initial concentration of both pathogenic microbes was 1×107 CFU/ml. After treatment for 10 mins, there was a significant reduction of more than 99% in the population of both the microbes. ● Furthermore, after treatment for 20 mins E. coli and S. aureus were reduced by 6.65±0.19 log 10 CFU/ml and 5.35±0.34 log 10 CFU/ml significantly. ● Similarly, after 20 mins, 95.5 % and 86 % of E. coli and S. aureus lost their metabolic activity.	Xu et al. 2018
8.	Spark plasma	10 kV at 30 Hz for 1, 3, 5, 7, 10, 12, 15 min	Both strains were cultured in PCA and later artificially incorporated in water	● E. coli ● E. faecalis	● pH	● Significant reduction of 8 log from 108CFU/ml was observed in E. coli and E. faecalis after treating for 15 and 12 mins, respectively. ● Furthermore, this reduction was 1 log and 3 log in E. coli and E. faecalis during storage periods of 12 mins and 10 mins, respectively. ● Sudden decrease by 51% was observed in pH.	Rashmei et al. 2016
9.	Dielectric Barrier Discharge	5 kV at 8kHz for 0, 2.5, 5, 10 min	Prepared yeast cells in exponential phase were incorporated in sterile ionized water	● Wild-type strain of S. cerevisiae	● pH ● MDA content	● With an increase in treatment time, the load of live cells was decreased from 95.20% to 10.89% while the number of dead and injured cells increased from 2.25% to 70.96% and 1.94% to 16.89%, respectively. ● Furthermore, after 10 mins treatment time the decrease in survival rate was maximum (19.0 %). ● Similarly, after 10 mins, a reduction of about 39 % was observed in pH. ● After treatment, an increase in MDA content was observed indicating plasma discharge can affect cell membrane leading to lipid peroxidation.	Xu et al. (2021)
10.	CAP	0.56 kV for 0, 1, 3 and 5 min	Prepared yeast cells in exponential phase were incorporated in sterile ionized water	● Wild-type strain of S. cerevisiae	● Cell morphology ● Cell membrane integrity ● MDA content	● After 1 to 5 mins, a significant reduction from 40.2 % to 1.5 % was observed in survival rate of cells. ● Furthermore, after 5 mins treatment, physical destruction and formation of cell debris was observed in treated cells. MDA content was increased by 2.65-fold compared to controlled samples. ● Leakage ratio of DNA/RNA was also increased significantly with increase in treatment time. Hence a damage in cell membrane integrity was observed.	Xu et al. (2020)
11.	CAP	8.36 kV at 23 kHz for 5 and 10 min	Prepared culture of virus was incorporated in PAW treated for 5 & 10 mins	Pseudo virus incorporated with SARS-Co-V-2 S protein	_	● In controlled samples, RLU value of hACE2-CoS-7 & hACE2-HEK-293T cells were 24,071 & 271,295, while in treated (PAW for 5 & 10 mins) pseudo virus it was 13.4 and 13.2 & 21.2 and 16.8, respectively. ● Significant inactivation of S protein in pseudo virus was observed after treatment leading to its aggregation. ● RLU value of treated pseudo virus was around more than 500 times lower than that in controlled samples. ● Furthermore, RBD of treated samples (PAW for 5 & 10 mins) was about 270 times higher than that in untreated samples (370ng/ml). Hence, a significant destruction of RBD was observed after treatment inhibiting its binding with hACE2.	Guo et al., (2020)
12.	CAP	0.2 W/cm2 for 0, 20, 40, 60, 80, 100, 120 s	The purchased strains of bacteriophage were cultured artificially for direct plasma treatment & also incorporated in PAW for the same	● T4 bacteriophage (double-stranded DNA) ● ø174 bacteriophage (single-stranded DNA) ● MS2 bacteriophage (RNA)	● Morphology	● After direct plasma treatment for 40s, reduction in PFU from 8.7×1010 to 3.7×105PFU/ml was observed, while after 80s treatment time there was 99.99% inactivation and further treatment for 100 s completely destroyed the infectivity of T4 bacteriophage. ● Similarly, incorporation of T4 bacteriophage in PAW brought a significant reduction of about 20 PFU/ml. ● Likewise, after 60 s plasma treatment there was complete inactivation of ø174 and MS2 bacteriophage. ● T4 got completely inactivated in PAW treated for 120 s, while ø174 and MS2 bacteriophage got inactivated in PAW treated for 80s. ● Disruption of both protein and DNA was observed in bacteriophages due to reactive species generated by plasma. ● T4 was critically aggregated and formation of large complexes was observed.	Guo et al. (2018)

PCA plate count agar; DBD-ACP dielectric barrier discharge-atmospheric cold plasma; FE-DBD floating electrode dielectric-barrier discharge; WWTP wastewater treatment plant; BOD biological oxygen demand; COD chemical oxygen demand; NTPnon-thermal plasma; DC direct current; LBLuria-Bertani;TSB tryptic soy broth; MDA malondialdehyde; PBSphosphate-buffered saline; CAP cold atmospheric pressure plasma; NTU nephelometric turbidity unit; CFUcolony-forming unit; PFUplaque-forming unit; RLU relative light unit; RBD receptor binding domain; PAWplasma-activated water; DNA deoxyribonucleic acid; RNA ribonucleic acid