MP-UV/CaO as a pretreatment method for the removal of carbamazepine and primidone in waste activated sludge and improving the solubilization of sludge.

Medium-pressure ultraviolet light (MP-UV) combined with calcium peroxide (CaO) as a pretreatment technology for removing carbamazepine (CBZ) and primidone (PMD) in waste active sludge (WAS) and improving the solubilization of sludge were investigated. CBZ and PMD were effectively removed and the removal fitted pseudo-first kinetics under MP-UV/CaO treatment with R > 0.97. The higher CaO dosage and lower initial volatile suspended solids (VSS) concentration were conductive to the removal of CBZ and PMD. Of the CaO hydrolysates, Ca(OH) played a more important role than HO during MP-UV/CaO treatment. The removal of the target compounds was attributed to direct photolysis and indirect photolysis caused by •OH, DOM, and O, in which •OH played a vital role with > 62.2% contribution to the overall degradation rate. A model predicting the steady concentration of •OH in WAS ([VSS] ≈ 8.6 g L) under MP-UV/CaO treatment with CaO dosage ranging from 0 to 0.5 g g-VSS was proposed and validated. Moreover, major intermediates of CBZ and PMD were detected and the probable transformation pathways during MP-UV/CaO treatment were proposed. In addition, MP-UV/CaO promoted the sludge solubilization effectively. Considering both the pharmaceutical degradation and sludge solubilization, the optimum operation condition with 0.2 g-CaO g-VSS combined with 7 h MP-UV irradiation is recommended. Under this condition, more than 92.3% of CBZ and 90.3% of PMD were removed, and soluble chemical oxygen demand (SCOD) increased by 657% and 13.6% compared with sole 10 h CaO (0.2 g g-VSS) treatment and 7 h MP-UV treatment, respectively.