Ultrasonic assisted activation of persulfate for the treatment of spent porous biochar: Degradation of adsorbed PFOA and adsorbent regeneration

In this work, the regeneration of spent biochar adsorbent and the degradation of adsorbed PFOA by the system of ultrasonic assisted activation of persulfate were explored. The effects of ultrasound, persulfate and biochar on PFOA removal were investigated through a series of regeneration and degradation experiments. Meanwhile, the degradation mechanism and reaction pathways of PFOA were investigated with electron paramagnetic resonance (EPR) and high-resolution quadrupole orbitrap mass spectrometer. The results showed that PFOA adsorbed by biochar could be degraded efficiently with the synergistic effect of ultrasound and persulfate. The degradation of PFOA in biochar could be finished in 4 h, while the defluorination took longer, with a defluorination efficiency of 50.6% after 4 h and 99.6% after 10 h. In this process, PFOA was degraded and defluorinated gradually by thermal decomposition caused by cavitation bubbles and degradation caused by the attack of SO4•ˉ and •OH. Two different free radicals controlled different degradation pathways, with SO4•ˉ playing a dominant role. In this system, the regeneration of the waste biochar adsorbent was achieved by eliminating PFOA, which could be recycled more than three times. The application potential of the system was evaluated using real water sample, and it was found that the removal of PFOA in real water sample was satisfactory even with the influence of inorganic ions and organic matter, indicating that it has promising application prospects. This work provided new insight into the degradation of adsorbed PFOA and adsorbent regeneration.