Degradation of emerging per- and polyfluoroalkyl substances (PFAS) using an electrochemical plug flow reactor.

In recent years, shorter-chain fluorinated compounds have been manufactured as alternatives to legacy per- and polyfluoroalkyl substances (PFAS) after a global ban on some long-chain PFAS. This study is the first to investigate the degradability of emerging PFAS by an electrochemical plug flow reactor (EPFR). Ten different emerging PFAS, representing classes of fluorotelomer alcohol, perfluoroalkyl ether carboxylate, polyfluoroalkyl ethersulfonic acids, perfluoroalkyl ether/polyether carboxylates, perfluoroether sulfonate, N-alkyl perfluoroalkylsulfonamido carboxylate, fluoroalkyl phosphonic acid, and perfluoro alkane sulfonamide were investigated. The process kinetics was performed. The degradation of parent compounds increased with increasing retention time (RT). At 45.2 min of RT, the degradation of parent compounds ranged between 68%-100% with a current density of 17.2 mA/cm2. A linear increase in pseudo-first order rate constants was observed for all PFAS with increasing current density from 5.7 to 28.7 mA/cm2 (R2 > 0.91). The effect of pH, natural organic matter, and bicarbonate on the degradation, defluorination, and fluorine mass balance are reported. Alkaline pH (11) caused a decrease in degradation for all PFAS. While the presence of natural organic matter (NOM) significantly decreased the degradation and defluorination processes, the presence of bicarbonate at all studied concentrations (25, 50, and 100 mg/L) did not affect the process efficiency. The defluorination reduced to 34% from 81% with 15 mg/L NOM. The unknown/undetected fluorine fraction also increased in the presence of 15 mg/L NOM indicating the formation of NOM-PFAS complexes. Additionally, C2-C8 perfluoro carboxylic acids (PFCAs), one perfluoro sulfonic acid (PFSA), two H-PFCAs, and 4:2 fluorotelomer sulfonate (FTS) were identified as degradation byproducts in suspect screening. The electrical energy per order for PFAS ranged between 1.8 and 19.4 kWh/m3. This study demonstrates that emerging types of PFAS can potentially be degraded using an EPFR with relatively low electrical energy requirements.

Occurrence and removal of poly/perfluoroalkyl substances (PFAS) in municipal and industrial wastewater treatment plants.

The presence of poly- and perfluoroalkyl substances (PFAS) has caused serious problems for drinking water supplies especially at intake locations close to PFAS manufacturing facilities, wastewater treatment plants (WWTPs), and sites where PFAS-containing firefighting foam was regularly used. Although monitoring is increasing, knowledge on PFAS occurrences particularly in municipal and industrial effluents is still relatively low. Even though the production of C8-based PFAS has been phased out, they are still being detected at many WWTPs. Emerging PFAS such as GenX and F-53B are also beginning to be reported in aquatic environments. This paper presents a broad review and discussion on the occurrence of PFAS in municipal and industrial wastewater which appear to be their main sources. Carbon adsorption and ion exchange are currently used treatment technologies for PFAS removal. However, these methods have been reported to be ineffective for the removal of short-chain PFAS. Several pioneering treatment technologies, such as electrooxidation, ultrasound, and plasma have been reported for PFAS degradation. Nevertheless, in-depth research should be performed for the applicability of emerging technologies for real-world applications. This paper examines different technologies and helps to understand the research needs to improve the development of treatment processes for PFAS in wastewater streams.

Electrooxidation of short and long chain perfluorocarboxylic acids using boron doped diamond electrodes.

This study investigates electrooxidation of short (C3-C6) and long (C7-C-18) chain perfluorocarboxylic acids (PFCAs) including perfluorooctane sulfonate (PFOA) using Si/BDD electrode. The effect of operational parameters (supporting electrolyte type, applied current density, and initial pH) were explored for PFOA removal. At the optimized conditions, 74% TOC removal and 37% defluorination ratio were gained for 10 mg L-1 of PFOA solution which evidences that the shorter chain PFCAs were formed. The PFOA degradation pathway followed one direct electron transfer from PFOA molecule to anode surface. Then two different degradation pathways were proposed. The first proposed degradation mechanism involved the reaction of perfluoroheptyl radical and hydroxyl radical, the release of HF and hydrolysis. The second mechanism involved the reaction between perfluoroheptyl radical and O2, formation of C7F15O and perfluorohexyl radical with releasing COF2. The removal of short- (C3-C6) and long-chain PFCAs (C7-C18) was also characterized. More than 95% of removal efficiency was gained for all long-chain PFCAs, excluding C7. The removal ratios of short-chain PFCAs (C3-C6) were 39%, 41%, 66% and 70% for C3, C4, C5 and C6, respectively. Contrary to long-chain PFCAs, chain-length dependence for short-chain PFCAs were observed. Defluorination ratio of short-chain PFCAs was only 45% signifying that defluorination partially occurred. Water matrix did not significantly affect the degradation of short-chain PFCAs in deionized water (DI), river water and secondary effluent of a wastewater treatment plant (WWTP). In contrast, defluorination ratio of long-chain PFCAs was noticeably affected by water matrix with the order of DI water > WWTP effluent > river water.

Electrochemical treatment of anti-cancer drug carboplatin on mixed-metal oxides and boron doped diamond electrodes: Density functional theory modelling and toxicity evaluation.

This study represents the electrooxidation of anti-cancer drug carboplatin (CrbPt) with different mixed metal oxide (MMO) and boron doped diamond (BDD) electrodes. The most effective anode was found as Ti/RuO2 with the complete degradation of CrbPt in just 5min. The effect of applied current density, pH and electrolyte concentration on CrbPt degradation has been studied. The degradation of CrbPt significantly increased at the initial stages of the process with increasing current density. However, further increase in current density did not affect the degradation rate. While complete degradation of CrbPt was provided at pH 7, the degradation rates were 49% and 75% at pH 9 and 4, respectively. Besides, increasing supporting electrolyte (Na2SO4) concentration provided higher degradation rate but further increase in Na2SO4 concentration did not provide higher degradation rate due to excess amount of SO4-2. According to the DFT calculations, the formation of [Pt(NH3)2 (H2O)2]2+ and [Pt(NH3)2 (OH)2] takes place with molecular weights of 265 and 263gmol-1, respectively. Toxicity of treated samples at BDD and Ti/RuO2 electrodes has been also evaluated in this study. The results showed that Ti/RuO2 anode provided zero toxicity at the end of the process.

Optimization and modelling using the response surface methodology (RSM) for ciprofloxacin removal by electrocoagulation.

In this study, response surface methodology (RSM) was used to investigate the effects of different operating conditions on the removal of ciprofloxacin (CIP) by the electrocoagulation (EC) with pure iron electrodes. Box-Behnken design was used for the optimization of the EC process and to evaluate the effects and interactions of process variables such as applied current density, process time, initial CIP concentration and pH on the removal of CIP by the EC process. The optimum conditions for maximum CIP removal (86.6%) were found as pH = 4; Co = 5 mg.L(1-); Id = 4.325 mA.cm(2-); tprocess = 10 min. The model adequacy and the validity of the optimization step were confirmed with additional experiments which were performed under the proposed optimum conditions. The predicted CIP removal as 86.6% was achieved at each experiment by using the optimum conditions. These results specify that the RSM is a useful tool for optimizing the operational conditions for CIP removal by the EC process.

An evaluation on different origins of natural organic matters using various anodes by electrocoagulation.

In this investigation, natural organic matters (NOM) of different origins (commercial, terrestrial and natural water) were treated by electrocoagulation (EC) process using aluminum, iron and hybrid electrodes. Electrode type effect on removal efficiency was observed for each NOM (commercial, terrestrial, and natural). The results were presented as dissolved organic carbon (DOC) (mg L(-1)) and UV/VIS absorbance (cm(-1)). The specific UV absorbance (SUVA) was determined before and after treatment of water. The lowest effluent concentration was obtained as 5.05 mg L(-1) with hybrid electrode for natural NOM source at its original pH 7.3. In addition, among the metal types, the best UV-abs-254 removal efficiency was obtained as 92.4% with 0.0312 cm(-1) by hybrid electrode at the end of the process. The color removal efficiency of water occurred successfully by Al and hybrid electrodes. Aquatic NOM source was the most resistant to EC treatment with DOC reduction of 71.1%, 59.8%, and 68.6% for Al, Fe and hybrid electrodes, respectively. Zeta potential and floc size of colloids were observed during the process for the determination of destabilization level of natural organic matters in EC process. Fast coagulation or flocculation and incipient instability were formed during electrolysis time for Al and Fe electrode, respectively. SUVA value was reduced to below 2 for three NOM sources studied. The EC process was shown to be a viable for different NOM sources with various metals.