Effectively remediating spiramycin from production wastewater through hydrolyzing its functional groups using solid superacid TiO₂/SO₄

Breaking down the structural bonds and eliminating the functional groups are more efficient than destroying the whole molecule in antibiotic production wastewater (APW) pretreatment before further biotreatment. Two sulfated titania (TiO₂/SO₄) solid superacids, SSA1 and SSA2 were synthesized, characterized and used for hydrolytic pretreatment of spiramycin in APW. Spiramycin removal followed an order of SSA2>SSA1>TiO₂≈pH = 3>control. The hydrolytic efficiencies increased at elevated temperature from 25 °C to 65 °C. The hydrolytic kinetics followed a first-order model and SSA2 performed the fastest. The performances were positively correlated with both the total acidity determined by n-butylamine titration and the strength of acid sites measured by NH₃-temperature-programmed desorption (TPD). The residual solution for SSA2 presented the least antibacterial potency and anaerobic inhibition among all treatments. The hydrolyzed product was identified as the m/z 699.4321 fragment using UPLC-Q/TOF-MS, which was formed after losing a functional mycarose moiety from the parent molecular. The solid superacids were effective in selectively eliminating 433 mg/L of spiramycin and the antibacterial potencies of the spiramycin production wastewater, which contained very high concentrations of COD (33,000 mg/L). This hydrolytic method avoids using and handling hazardous and corrosive mineral acids on site. It is attractive as a selective catalytic pretreatment method to cleave antibiotics’ functional groups and to reduce its inhibitory effects before sequential biotreatments.