Impact of ultrasonication on the regeneration of tetracycline-saturated activated carbon and activated coke using persulfate

Activated carbon (AC) and activated coke (ACO) are being widely applied in China for drinking water purification and advanced treatment of secondary effluent, respectively. A cost-effective approach for regenerating these exhausted carbons is crucial. The combined ultrasonication (US) and peroxydisulfate (PDS) process was proved effective for regenerating tetracycline(TC)-saturated carbons. Optimal PDS concentration and regeneration time were identified while the regeneration efficiencies were stable across a wide initial solution pH range. Raman spectral intensity of the regenerated ACO is higher than that of the pristine ACO, while the intensity of the regenerated AC is particularly lower than that of the pristine AC. After US-PDS regeneration,the saturated ACO and AC retained 70.6 % and 46.7 % of their initial specific surface area, respectively. The average pore size of ACO decreased from 3.24 nm to 2.62 nm, while that of AC increased from 2.50 nm to 2.80 nm. Additionally, the proportion of micropores on ACO increased from 54.19 % to 66.98 %, while it decreased from 57.32 % to 49.16 % on AC. Consecutive adsorption-regeneration demonstrated similar regeneration performance for both carbons, with ACO being more practical due to its lower price and predominantly mesoporous structure. Both superoxide radicals (O2·-) and singlet oxygen (1O2) played the significant roles, with 1O2 contributing particularly highly in the US/ACO-PDS process. The regeneration of TC-saturated ACO and AC by US-PDS process primarily involves TC stripping and oxidation enhanced by ultrasonic waves and PDS.