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Sustainability 2022, 14, x FOR PEER REVIEW 9 of 37

Plasma is an ionised gas formed by the addition of energy, which causes the gas molecules to ionise 256

[71]. Highly reactive oxidative and reductive species are generated in plasma-based water treatment in 257
response to an electrical discharge created between two electrodes in the presence of liquid water [72- 258

74]. Furthermore, temperature rises near the discharge, shockwaves are generated, and UV light is 259
emitted inside the reactor. Non-thermal plasma (NTP) is superior for treating PFAS-contaminated 260

water because it uses less energy at atmospheric pressure and has greater excitation selectivity and 261

energy efficiency than thermal plasma [75, 76]. The Figure 4 explains the process of the technique 262
plasma discharge. 263

Numerous techniques, including spark discharge, corona discharge, glow discharge, dielectric barrier 264
discharge, and gliding arc discharge, can be used to produce the NTP. The energised electrons will 265

have a temperature that is substantially higher than the ambient gases. Due to the continual collisions 266
between the electrons and the gas's atoms, electrons, radicals, ions, and photons are produced [76]. The 267

positively or negatively charged portions of the PFAS molecules are adsorbed onto the water-bubble 268

interface, where they clash with the ions with the greatest energies in the plasma state [77, 78]. There 269
are no further chemicals needed to finish the therapy because the plasma discharge is a complete 270

procedure [75]. The ideal plasma reactor for treating chemicals that behave like surfactants, such 271

PFAAs [79, 80], has reportedly been identified as argon bubbling. The effectiveness of the Plasma 272
technology varies greatly. It is dependent on multiple variables, including the reactor, electrode material, 273

conductivity, voltage applied, type of PFAS, liquid conductivity, pH of the solution, gas input, pulse 274
repetition rate, and input of energy. 275

276

PFAS removal in Plasma is more significant than other major water treatment methods [80, 81]. Another 277

benefit is the quick treatment time compared to other PFAS degrading methods. According to research by 278

Singh et al., co-contaminants have no effect on how well PFAS can be treated using plasma technology [74]. 279

The plasma-liquid interface is where most of the chemic al reaction takes place, as demonstrated by Stratton 280

et al. As a result, plasma-based water treatment appears to be less sensitive to the presence of organic and 281

inorganic co-contaminants than most other treatment techniques [80]. Singh et al. also observed that the 282

plasma treatment method seems to be a viable and effective approach for eliminating PFAS from high 283

conductivity water [80]. Both short-chain and long-chain PFAS can be successfully removed by NTP, while 284

short-chain PFAS compounds require longer treatment periods than long-chain PFAS compounds. Some 285

aspects of the effluent, such as pH, OM content, and nitrate concentration, can directly lower the effectiveness 286