Novel iron-carbon micro-electrolysis-anoxic/oxic biofilter system for enhanced treatment of tetracycline wastewater: Significant reduction of antibiotic-resistant and pathogenic bacteria

To mitigate the toxicity of tetracycline (TET) to functional microorganisms and avoid the exceeded discharge of tetracycline-resistant bacteria (TRB), a novel combined iron-carbon micro-electrolysis-anoxic/oxic biofilter (Fe–C-AOBF) system for treatment of pharmaceutical wastewater with high TET concentration was successfully established. Results showed that Fe–C-AOBF had the higher maximum tolerated concentration and the stronger degradation ability for TET than normal biological treatment system. When influent COD, NH4–N and TET were 4000, 200 and 100 mg/L, their removal efficiencies via Fe–C-AOBF could reach 96%, 86% and 90%, respectively. Microbial community analysis revealed micro-electrolysis pretreatment in Fe–C-AOBF system improved the microbial diversity compared to up-flow anaerobic/oxic biological aerated filter (UAF–UBAF). The relative abundance of dominate bacteria with tetracycline resistance genes (TRGs) in the biofilm of Fe–C-AOBF, such as Comamonadaceae, Thauera, Sinobacteracea, Acidaminobacter, and Enterobacteriaceae, was also decreased. Moreover, the absolute concentrations of five normal TRGs in effluent of Fe–C-AOBF were reduced by about 16 orders of magnitude as compared to UAF-UBAF. Due to approximately 70% of original TET has been degraded in micro-electrolysis process and lost its selective pressure to microorganisms, Fe–C micro-electrolysis played a key role in restraining the formation and reproduction of TRB and eliminating the potential risk of pathogenic bacteria (e.g., Arocobacter)in AOBF. Fe–C-AOBF system provided an efficient, stable and green method for antibiotic wastewater treatment with the function of inhibiting the emergence of antibiotic-resistant bacteria.