Efficient decomposition of perfluorooctane sulfonic acid in water using plasma and sulfate radical anions

Summary form only given. Perfluorooctane sulfonic acid (PFOS: C₇F₁₅SO₃H) is an excellent surface-active agent and has been widely used in various applications. However, PFOS is a bioaccumulating substance and has toxic effects on the human body. We recently found that plasma generated in gas bubbles can decompose PFOS very efficiently and rapidly [1]. During the PFOS decomposition process using plasma, perfluorocarboxylic acids (PFCAs: CnF_2n+1COOH) with shorter carbon chains (n = 1-6) are generated in water as byproducts. Although the plasma can also decompose the PFCAs, the decomposition rates for PFCAs with short carbon chain (n = 1-3) are very low because of the lower interfacial activity. Persulfate (S₂O₈^2-)-added hot-water treatment is another method to decompose PFCAs, which uses sulfate radical ion (SO₄^-): a strong oxidant. This treatment cannot decompose PFOS but can decompose PFCAs with short carbon chain efficiently and rapidly. Thus, the combination use of the plasma and persulfate-added hot-water treatments was performed to achieve efficient and rapid decomposition of PFOS and the by-products. The decomposition efficiency was evaluated using the amount of fluoride ions detached from PFOS and the PFCAs per energy consumption. Firstly, 20 mL of PFOS solution at an initial concentration of 61.0 mg/L was treated using dc plasma in oxygen bubbles at a current of 10 mA and an average power of 11 W. After 170 min, the PFOS concentration decreased by 99%. Then, Na₂S₂O₈ was added to the solution at a S₂O₈^2- concentration of 100 mmol/L. The solution was heated using a mantle heater, up to 353 K, at which temperature SO₄^- can be obtained from S₂O₈^2- thermally. The average power of the heater was 52 W. After 70 min, PFOS and the by-products werSummary form only given. Perfluorooctane sulfonic acid (PFOS: C₇F₁₅SO₃H) is an excellent surface-active agent and has been widely used in various applications. However, PFOS is a bioaccumulating substance and has toxic effects on the human body. We recently found that plasma generated in gas bubbles can decompose PFOS very efficiently and rapidly [1]. During the PFOS decomposition process using plasma, perfluorocarboxylic acids (PFCAs: CnF2n+1COOH) with shorter carbon chains (n = 1-6) are generated in water as byproducts. Although the plasma can also decompose the PFCAs, the decomposition rates for PFCAs with short carbon chain (n = 1-3) are very low because of the lower interfacial activity. Persulfate (S₂O₈^2-)-added hot-water treatment is another method to decompose PFCAs, which uses sulfate radical ion (SO₄^-): a strong oxidant. This treatment cannot decompose PFOS but can decompose PFCAs with short carbon chain efficiently and rapidly. Thus, the combination use of the plasma and persulfate-added hot-water treatments was performed to achieve efficient and rapid decomposition of PFOS and the by-products. The decomposition efficiency was evaluated using the amount of fluoride ions detached from PFOS and the PFCAs per energy consumption. Firstly, 20 mL of PFOS solution at an initial concentration of 61.0 mg/L was treated using dc plasma in oxygen bubbles at a current of 10 mA and an average power of 11 W. After 170 min, the PFOS concentration decreased by 99%. Then, Na₂S₂O₈ was added to the solution at a S₂O₈^2- concentration of 100 mmol/L. The solution was heated using a mantle heater, up to 353 K, at which temperature SO₄^- can be obtained from S₂O₈^2- thermally. The average power of the heater was 52 W. After 70 min, PFOS and the by-products were completely decomposed. The combination use of the treatments achieved double energy efficiency and decreased the total treatment time for the complete decomposition by half compared to the treatment using only plasma.e completely decomposed. The combination use of the treatments achieved double energy efficiency and decreased the total treatment time for the complete decomposition by half compared to the treatment using only plasma.