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Sustainability 2022, 14, x FOR PEER REVIEW 7 of 37

GAC is effective in removing long chain PFASs and can lower PFAS levels in drinking water to ng/L. 191

GAC is not selective and becomes partially saturated with other organic chemicals, therefore it cannot 192
be utilised for water that includes them. In addition, short chain PFAS leak through, and inorganic 193
chemicals are not removed. Additionally, using GAC is very expensive. 194

3.2 Ion-Exchange Resins 195

IXR is better than GAC at removing PFASs at the ng/L level, including anionic and long chain PFASs, 196

and has a higher adsorption capacity. However, it is also not particularly effective against water that 197
has large levels of total dissolved solids (TDS) and/or organic materials found naturally. Additionally, 198

it has reduced affinity for short-chain PFASs, and this method necessitates burning the ion exchange 199
resin. The detailed process is explained in figure 3. 200

3.3 Nano-Filtration and Reverse Osmosis 201
Nano-filtration and reverse osmosis are effective for both short and long chain PFASs and can treat all 202

types of water contaminated with PFASs. But the membrane used in Nano-filtration and reverse 203

osmosis is affected when treating inorganic compounds. Separation technologies such as IXR and GAC 204
can only remove the PFAS from a specific medium; however, they remain in the environment and 205

continues to cause health risks. he most popular or commonly accepted methods for PFAS removal 206

from drinking water and ground now are GAC and IXR. The greater adsorption capabilities of IXR, 207
along with shorter contact durations and lower equipment footprints, are making IXR applications more 208

attractive than GAC applications even though IXR systems are more costly. More crucially, although 209
the on-site regeneration of GAC is impractical, IXR may be regenerated on-site to a practically virgin 210
capacity and afterwards utilised frequently. 211

These technologies don’t destroy the PFASs, they only separate them from the contaminated water on 212

adsorbent materials or in concentrated brine. The disposal of these absorbent materials or this brine 213

could lead to secondary contamination. The high amounts of PFASs produced by IXR technology are 214
now being held in safe locations across the world until an appropriate disposal method is found. The 215

destruction of PFASs also depends on their fluoroalkyl chain lengths. Currently there is no method 216
being used, however there are many that have been developed and have shown promise in destroying 217

PFAS. These methods are Electrochemical oxidation, Plasma, Photocatalysis, Sonolysis, Supercritical 218
water oxidation, and Thermal degradation/incineration. 219

3.4 Electrochemical Oxidation Process 220

The Electrochemical Oxidation (EO) process oxidises organic pollutants present by applying an 221
electrical current through a conductive solution between an anode and a cathode and. Contaminants are 222

absorbed and destroyed either in the liquid media or at the electrode [48, 49]. Through both direct and 223