## 4 Electrochemical Aqueous Remediation of Fluorinated Compounds
[PERSON] et al., (2019) also investigated the degradation of PFOS by using a microporous REM composed of Magneli phase titanium suboxide [118]. To assess the performance of the REM, they ran a 2.0 uM PFOS solution with varying current density of 0.5 to 4.0 mA/cm\({}^{2}\). By comparing REM operation to a batch operation mode at an anodic potential of 3.15 V, they were able to remove 98.30% \(\pm\) 0.51% of PFOS under REM operation, a much higher efficiency than what was achieved using the batch operation mode. Their results showed that PFOS degradation formed intermediate products such as short-chain PFACs in trace amounts and underwent rapid mineralization to form carbon dioxide and fluoride. Using density functional theory simulations, they found that PFOS degradation was initiated by direct electron transfer on the anode yielding PFOS free radicals. Then, these PFOS free radicals further reacted with hydroxyl radicals, an essential component to PFOS degradation, because PFOS free radicals had the potential to react with water and reform as PFOS. Future work for this study includes scaling the REM system to remediate larger quantities of PFOS-contaminated water. Another technique recently applied to PFAS-contaminated water is a unique separation technique. The most important separation technique is electrocoagulation (EC) which involves the addition of charged metal hydroxides to a colloid in order to disrupt the electrostatic charges of its components, resulting in separation from the aqueous phase. EC has already been used to remove heavy metals, suspended solids, bacteria, oils, and other contaminants from water, but has been relatively unexplored in its ability to remove PFASs from water sources. An early attempt to optimize the EC technique for the removal of PFOS/PFOA from water came from [PERSON] et al., (2013), who sought to examine the parameters of: flocculation time, initial contaminant concentration, concentration of dissolved organic material, coagulant dosage, and solution pH and their effects on the efficiency of removing PFOS/PFOA contaminants from water [119]. [PERSON] conducted a series of jar tests on prepared solutions containing deionized water and organic material from the Suwannee River, Florida, USA, that were spiked with 0.2 uM of both PFOS and PFOA. After preparing their solutions, they were coagulated using either alum or ferric chloride at various dosages and initial pHs before being filtered through a Millipore membrane. These membranes were then analyzed using LC/MS to determine the efficiency of removal of PFOS/PFOA under their respective conditions. Their testing concluded that coagulant dosage and initial solution pH were the two dominant factors affecting the efficiency of PFOS/PFOA removal as the dosage determines the surface area available for adsorption as well as pH determines the number of protonated adsorption sites. As shown in Figure 3, [PERSON] et al., developed an operational coagulation diagram depicting the optimal operating conditions for the removal of PFOS/PFOA [119]. After optimizing the EC technique to efficiently filter PFASs such as PFOS and PFOA from water, the focus became overcoming the challenge of long-term use of a single electrode leading to passivation and a drop in removal efficiency. A novel solution to this was developed by [PERSON] et al., (2018), who modified the existing methodology by incorporating the periodically reverse electrocoagulation (PREC) technique [120]. [PERSON] sought to determine the effectiveness, energy consumption, and application to contaminated natural groundwater using various electrode materials, applied voltages, and stirring speeds. To accomplish this, they utilized a PREC reactor with duo combinations of iron, zinc, and aluminum electrodes to treat contaminated water as well as LC/MS to determine the efficiency of removal of PFOS/PFOA and FTIR to confirm the identity of the flocs formed.