Nano iron tetroxide-modified rice husk biochar promoted Feammox performance of Klebsiella sp. FC61 and synergistically removed Ni2+and ciprofloxacin

The iron reduction coupled with ammonia oxidation process (Feammox) is a biological reaction process asso-ciated with the nitrogen cycle that has been discovered in recent years. In this study, the iron-reducing bacterium Klebsiella sp. FC61 was attached by synthesizing nano-loadings of iron tetroxide (nFe3O4) onto rice husk biochar (RBC), and the RBC-nFe3O4 was used as an electron shuttle to participate in the biological iron reduction process of soluble and insoluble Fe3+ to improve the ammonia oxidation efficiency to 81.82%. This acceleration of electron transfer increased the carbon consumption rate and further tuned up the COD removal efficiency to 98.00%. The Feammox could be coupled with iron denitrification for internal nitrogen/iron cycling to reduce the accumulation of nitrate by-products and achieve the recycling of iron. In addition, pollutants such as Ni2+, ciprofloxacin, and formed chelates could be removed by pore adsorption and pi-pi interactions using bio-iron precipitates produced by iron-reducing bacteria.

Automated summary

In this study, iron-reducing bacteria were attached to rice husk biochar by synthesizing nano-loadings of iron tetroxide, which improved the ammonia oxidation efficiency to 81.82%. The electron shuttle provided by the biochar increased the carbon consumption rate and further improved the COD removal efficiency to 98.00%. Additionally, the Feammox process coupled with iron denitrification can reduce nitrate accumulation and achieve nitrogen/iron recycling.