Mitigating mechanism of nZVI-C on the inhibition of anammox consortia under long-term tetracycline hydrochloride stress: Extracellular polymeric substance properties and microbial community evolution

In this study, activated carbon-loaded nano-zero-valent iron (nZVI-C) composites were added to anaerobic ammonium oxidation bacteria (AnAOB) to overcome the inhibition of tetracycline hydrochloride (TCH). Results showed that 500 mg L-1 nZVI-C effectively mitigated the long-term inhibition of 1.5 mg L-1 TCH on AnAOB and significantly improved the total nitrogen removal efficiency (TNRE) (from 65.27% to 86.99%). Spectroscopic analysis revealed that nZVI-C increased the content of N-H and C--O groups in EPS, which contributed to the adsorption of TCH. The accumulation of humic acid-like substances in EPS was also conducive to strengthening the extracellular defense level. In addition, TCH-degrading bacteria (Clostridium and Mycobacterium) were enriched in situ, and the abundance of Ca. Brocadia was significantly increased (from 10.69% to 18.59%). Furthermore, nZVI-C increased the abundance of genes encoding tetracycline inactivation (tetX), promoted mineralization of TCH by 90%, weakening the inhibition of TCH on microbial nitrogen metabolism. nZVI-C accelerated the electron consumption of anammox bacteria by upregulating the abundance of electron genera-tion genes (nxrA, hdh) and providing electrons directly.

Automated summary

This study demonstrated that the addition of activated carbon-loaded nano-zero-valent iron (nZVI-C) composites could overcome the inhibition of tetracycline hydrochloride (TCH) on anaerobic ammonium oxidation bacteria (AnAOB). The results showed that 500 mg L-1 nZVI-C effectively mitigated the long-term inhibition of 1.5 mg L-1 TCH on AnAOB and significantly improved the total nitrogen removal efficiency (TNRE) from 65.27% to 86.99%. Spectroscopic analysis revealed that nZVI-C increased the content of N-H and C--O groups in EPS, which contributed to the adsorption of TCH. The accumulation of humic acid-like substances in EPS was also conducive to strengthening the extracellular defense level. Furthermore, TCH-degrading bacteria (Clostridium and Mycobacterium) were enriched in situ, and the abundance of Ca. Brocadia was significantly increased from 10.69% to 18.59%. Additionally, nZVI-C increased the abundance of genes encoding tetracycline inactivation (tetX) and promoted the mineralization of TCH by 90%, weakening the inhibition of TCH on microbial nitrogen metabolism. nZVI-C accelerated the electron consumption of anammox bacteria by upregulating the abundance of electron generation genes (nxrA, hdh) and providing electrons directly.