Fate of perfluorooctanoic acid (PFOA) in sewage sludge during microwave-assisted persulfate oxidation treatment

Abstract

The fate of perfluorooctanoic acid (PFOA) has been investigated for an emerging sludge treatment technique using microwave heating-assisted persulfate (PS) oxidation. The effect of heating temperature (20, 50, and 70 °C) and PS dose (PS1: 0.01; PS2: 0.1; PS3: 0.2 g/g wet sludge) was studied in sludge spiked with PFOA at an environmentally relevant concentration (200 ng/g wet weight). Control degradation experiments using spiked sludge without PS addition and background sludge (no PFOA spike) with PS addition were also conducted at each temperature. Sludge samples were analyzed for eight perfluorocarboxylic acids (PFCAs) (C4 – C11) using LC-MS/MS. At 20 °C (PS2 dose), minimal (~ 5%) removal of the spiked PFOA was observed after 72 h, suggesting the need for elevated treatment temperature. For the same PS dose (0.1 g /g sludge), treatment at 50 and 70 °C showed a decrease in PFOA concentration with increasing temperature, with ~ 28 and ~ 42% removal following 4 h of treatment. No significant increase in degradation was observed for the highest dose (PS3) after 2 h, possibly indicating self-scavenging of PS at high dosage. Due to the low initial spiking concentration of PFOA and low extraction recovery, all shorter-chain PFCAs (< C8), the degradation products of PFOA, were below quantification limits in all sludge samples.