Effects and mechanisms of oxytetracycline and norfloxacin on microbial extracellular polymeric substances (EPS) in biological denitrification of aquaculture wastewater.

The direct equalizing ray method was employed to design three groups of mixtures of oxytetracycline(OTC) and norfloxacin(NOR) with varying proportions(Group R1 had a higher proportion of OTC, while R2 had similar concentrations of both antibiotics, and R3 had a higher proportion of NOR).The effects of these mixtures on the content and properties of extracellular polymeric substances (EPS) in the biological denitrification process were investigated using an sequencing batch reactor activated sludge reactor (SBR). The results revealed that the removal rates of ammonia nitrogen(NH 3 -N) decreased in all three groups with the addition of antibiotics. As the antibiotic concentration increased, the EPS content decreased by 68.46%, 55.53%, and 65.03% in R1, R2, and R3, respectively. To understand the interaction mechanism of mixed antibiotics on EPS in activated sludge, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) techniques were employed. The findings demonstrated significant effects of mixed antibiotics on functional groups such as C-O, C O, and C-O-C. Specifically, hydrogen bonding was found to be the primary influencing factor in the R1 ratio, while Π-Π conjugation played a major role in the R3 ratio. [Display omitted] • High-concentration mixture of OTC and NOR inhibitory nitrogen removal performance of SBR. • High-concentration mixture of OTC and NOR reduced the production of extracellular polymeric substances. • High proportion of OTC, the EPS characteristics are mainly affected by hydrogen bonding interactions. • High proportion of NOR, the EPS characteristics are mainly affected by hydrogen bonding interactions and π-π conjugation. [ABSTRACT FROM AUTHOR]