# A Review of Treatment Techniques for Short-Chain Perfluoroalkyl Substances
## 3 Treatment Techniques for Short-Chain PFASs
### Adsorption Technique
#### 3.1.3 Coagulation and Electrocoagulation  
Coagulation possessed the advantage of low price and high adsorption efficiency [4]. [PERSON] et al. [35] discovered that the removal efficiency of PFOA exceeded 90% when the dosage of polymer aluminum chloride (PACI) was 10 mg/L. However, the removal efficiency of PFOA was reduced significantly when multiple PFASs existed simultaneously, and the removal rates followed the order of PFBA > PFHxA > PFOA > PFDoA > PFOS, which demonstrated that the removal efficiency of short-chain PFASs was superior, compared with long-chain congeners.  
Electrocoagulation received widespread attention because of its higher removal efficiency for PFASs and short treatment period [4]. The electrocoagulation technique mainly produced a large number of cations and then generated flocs by sacrificing the anode; thus, the dissolved contaminants could be purified by condensation and adsorption of flocs, which was subsequently carried to the surface of the solution by the H2 and O2 produced by the electrodes through electrical floating. The Electrocoagulation mechanism for PFAS removal is shown in Figure 2. [PERSON] et al. [36] adopted the periodically reversing electrocoagulation (PREC) technique to treat contaminated groundwater around fluorochemical plants, indicating that the PREC was effective for the removal of PFASs with different lengths of carbon chains. Subsequently, the above group approved that the PREC technique with Al-Zn electrodes for multiple PFSA removal was impactful, the removal rates of PFBS, PFHxS, and PFOS could reach up to 87.4%, 95.6%, and 100% within 10 min underoptimal conditions (12.0 V, pH = 7, 400 r/min) [37]. In general, the removal mechanism of electrocoagulation was a hydrophobic effect and might exist with electrophoretic, polarized, and electric fields [38]. In addition, several influencing factors involving current density, inorganic ions, and OM were also crucial for the removal of short-chain PFASs.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**adsorbent**} & \multirow{2}{*}{\begin{tabular}{c} **adsorbent** \\ **Dose/(mg/L)** \\ \end{tabular} } & \multirow{2}{*}{**PFASs**} & \multicolumn{2}{c}{**PFAS**} & \multirow{2}{*}{**Experiment**} & \multirow{2}{*}{**Removal Efficiency**} & \multirow{2}{*}{**References**} \\  & & & & & & \\ \hline GAC (F400) & 1000 & PFBS & 15–150 & \begin{tabular}{c} DI, 30 \({}^{\circ}\)C, \\ pH = 7.2 \\ \end{tabular} & 98.7 mg/g & [23] \\ \hline BdAC & 200 & PFHxA & 31.4 & \begin{tabular}{c} WW, 25 \({}^{\circ}\)C \\ pH = 4, 48 h \\ pH = 4, 48 h \\ pH = 4, 48 h \\ pH = 4, 48 h \\ 170 r/min \\ \end{tabular} & 18.84 mg/g & [25] \\ \hline IRA67 & 100 & PFHxA & 31.4 & \begin{tabular}{c} WW, 25 \({}^{\circ}\)C \\ pH = 4, 48 h \\ 170 r/min \\ \end{tabular} & 37.68 mg/g & [25] \\ \hline AC (micropore) & 250 & \begin{tabular}{c} PFBA \\ \end{tabular} & 6.5–204 & \begin{tabular}{c} DI, room \\ temperature \\ pH = 6, 3 d \\ \end{tabular} & \begin{tabular}{c} 51.36 \(\pm\) 4.28 mg/g \\ \end{tabular} & [26] \\ \hline CTF & 250 & PFBA & 6.5–204 & \begin{tabular}{c} DI, room \\ temperature \\ pH = 6, 3 d \\ \end{tabular} & 92.03 \(\pm\) 4.28 mg/g & [26] \\ \hline SWCNT & 250 & PFBA & 106.4 & \begin{tabular}{c} DI, 25 \({}^{\circ}\)C \\ pH = 7, 2 d \\ 200 r/min \\ \end{tabular} & 7.5\% & [30] \\ \hline IRA910 & 100 & \begin{tabular}{c} PFBS \\ \end{tabular} & 50–400 & \
\begin{tabular}{c} DI, 25 \({}^{\circ}\)C, \\ pH = 6, 240 h \\ 160 r/min \\ \end{tabular} & 635.69 mg/g & [34] \\ \hline Electrocoagulation & – & PFBS & 0.031 &
\begin{tabular}{c} GW, pH = 7.0 \\ 10 min, 400 r/min \\ Al-Zn, 12 V \\ \end{tabular} & 87.4\% & [36] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparisons on adsorption capacities of various adsorbents for short-chain PFASs.  
Figure 2: Electrocoagulation Mechanism for PFASs removal.