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enabling high treatment efficiencies for all effluents [94]. This technology is also seen as environmentally 343
friendly as it does not allow for the formation of NOx and SOx compounds that are highly toxic. 344

Even though SCWO works well with high volumes of effluents, it is not economically viable to treat more 345

than 50,000 gallons/day of diluted waste streams due to the heat required. Not only the heat, but also the mass 346

transfer, and the large volume that has to be pumped requiring extra costs [92]. During oxidation, SCWO also 347

produces a large variety of acids (H2SO4, HCl) resulting in pH reduction cause the corrosion of the reactor. 348

Another major issue is the precipitation of salts on the wall of the reactor. 349

350

3.8 Thermal Treatment 351

Heat is used in thermal treatment to treat, degrade, and/or destroy materials. This process is quite complex 352

and is influenced by several factors. These variables include the reaction chamber's environment, the target 353

effluent's chemical properties, and the operating parameters, which include the gases present, temperature, 354

residence time, and residence time. The optimum process for incineration of PFAS is mineralization, which 355

results in the by-products of carbon dioxide, water, carbon monoxide, and hydrogen fluoride. Because PFASs 356

are physically and chemically stable, they need more time and greater temperatures to degrade. As a thermal 357
oxidation treatment process, incineration is performed at high temperatures in an oxygen-rich environment. 358

Typically, hazardous waste incinerators run between 980 and 1200 °C [95]. However, because the majority 359

of organic compounds are destroyed thermally between 590 and 650 °C, it is predicted that almost all organics 360
in the fluid, including PFASs, will be eliminated [95]. 361

The U.S. EPA [96] produced a brief regarding the incineration of PFAS in 2020, with the major finding being 362

that it is unclear how well PFAS are destroyed by incineration and what would happen to them in terms of the 363

production of mixed fluorinated organic by-products. The possibility of PIC (products of incomplete 364

combustion), which might pose a risk, forming as a result of the incomplete destruction of PFAS is a serious 365

concern. According to Solo-Gabriele et al., raising the incinerator's temperature reduced the overall amounts 366

of PFAS that were treated. Not all PFAS species, however, experienced a reduction with rising temperatures 367

[97]. The public is concerned that the incinerator may spread PFAS rather than removing it because of high 368

quantities of PFOA discovered in the air nearby the incineration site [98, 99]. Waste by-products that undergo 369

incineration include bottom ash. This bottom ash consists of non-combusted products, containing volatile 370