Removal of phenolic endocrine disrupting compounds from waste activated sludge using UV, H₂O₂, and UV/H₂O₂ oxidation processes: Effects of reaction conditions and sludge matrix

Removal of six phenolic endocrine disrupting compounds (EDCs) (estrone, 17β-estradiol, 17α-ethinylestradiol, estriol, bisphenol A, and 4-nonylphenols) from waste activated sludge (WAS) was investigated using ultraviolet light (UV), hydrogen peroxide (H₂O₂), and the combined UV/H₂O₂ processes. Effects of initial EDC concentration, H₂O₂ dosage, and pH value were investigated. Particularly, the effects of 11 metal ions and humic acid (HA) contained in a sludge matrix on EDC degradation were evaluated. A pseudo-first-order kinetic model was used to describe the EDC degradation during UV, H₂O₂, and UV/H₂O₂ treatments of WAS. The results showed that the degradation of the 6 EDCs during all the three oxidation processes fitted well with pseudo-first-order kinetics. Compared with the sole UV irradiation or H₂O₂ oxidation process, UV/H₂O₂ treatment was much more effective for both EDC degradation and WAS solubilization. Under their optimal conditions, the EDC degradation rate constants during UV/H₂O₂ oxidation were 45–197 times greater than those during UV irradiation and 11–53 times greater than those during H₂O₂ oxidation. High dosage of H₂O₂ and low pH were favorable for the degradation of EDCs. Under the conditions of pH = 3, UV wavelength = 253.7 nm, UV fluence rate = 0.069 mW cm⁻², and H₂O₂ dosage = 0.5 mol L⁻¹, the removal efficiencies of E1, E2, EE2, E3, BPA, and NP in 2 min were 97%, 92%, 95%, 94%, 89%, and 67%, respectively. The hydroxyl radical (·OH) was proved to take the most important role for the removal of EDCs. Metal ions in sludge could facilitate the removal of EDCs during UV/H₂O₂ oxidation. Fe, Ag, and Cu ions had more obvious effects compared with other metal ions. The overall role of HA was dependent on the balance between its competition as organics and its catalysis/photosensitization effects. These indicate that the sludge matrix plays an important role in the degradation of EDCs. - Highlights: • UV/H₂O₂ is effective in removing EDCs from WAS and improve sludge solubilization. • EDC degradation in sludge fitted well with pseudo-first-order kinetics. • ·OH takes the most important role in UV/H₂O₂ oxidation of EDCs in sludge. • Metal ions in sludge facilitate the removal of EDCs during UV/H₂O₂ oxidation. • Effect of HA in sludge on EDC removal during UV/H₂O₂ oxidation is observed