Page 11 - report

Sustainability 2023, 15, x FOR PEER REVIEW 3 of 37

it feasible to use sunlight as a sustainable energy source [85, 86]. Figure 5 gives the idea about the removal of 315
PFAS using photocatalysis. 316

Additionally, changes to these photocatalysts' semiconductor-based chemical compositions, their 317

morphologies, and their sizes can drastically improve PFAA removal and mineralization. Due to its high 318

reactivity, cheap cost, decreased toxicity, and chemical stability, TiO2 is also near to a perfect catalyst due to 319

its photocatalytic and hydrophilic properties [87]. Photocatalytic treatment is a potential technique that may 320

be performed at a variety of ambient temperatures and requires less energy than other treatments [88]. Due to 321

its low energy consumption and potential for using green energy, photocatalysis is also seen to be a highly 322

sustainable process in contrast to AOP and ARP technologies. The catalyst can also be recycled, in addition 323

[89]. In contrast to other PFAS mineralization methods, photocatalysis has comparatively low efficiency. It 324

works better for PFOA and has minimal effect on PFOS. TiO2 is unsuccessful for PFOS absorption because 325

it functions mostly in the UV region, which is unfavourable for absorption [82]. TiO2 recovery from the 326

treated solution is also challenging and complicated [90]. Lastly, the presence of co-contaminants effects the 327

process, which may cause to significantly lower the degradation efficiency [91]. 328

3.7 Supercritical Water Oxidation 329

Supercritical water oxidation (SCWO) is an oxidation treatment method that converts OM into water, carbon 330

dioxide, and a few additional products depending on the waste stream. Dewatering is not necessary for the 331

treatment of a wide variety of wet waste. Additionally, this approach has shown to be successful in eliminating 332

PFASs and other harmful and persistent organic pollutants [92]. Supercritical water is reached at above 374 333

degrees Celsius and 218 atm. It is a condition where organic solubility is significantly improved and oxidation 334

is promoted [93, 94]. The fluid is neither a liquid nor a gas at this extremely important point, but exhibits 335

characteristics of both. Since there are no separate gas phases or all liquid phases in supercritical water, and 336

have unlimited mass transfer, promoting chemical processes. Organic molecules, such as PFASs, that do not 337

oxidise at normal temperatures and pressures can be broken down by super critical oxidations [93]. 338

SCWO is a highly destructive treatment in which the compounds treated are degraded to simple elements and 339

there are no reaction by-products, incompletely oxidised impurities, or unreacted hazardous accidents. Super 340

critical water oxidation is comparatively quicker than other technologies, enabling it to treat huge quantities 341

of wastewater at a cheap cost. Additionally, this method is unaffected by the presence of co-contaminants, 342