Valorization of oxytetracycline fermentation residue through torrefaction into a versatile and recyclable adsorbent for water pollution control

Antibiotics fermentation residue (AFR) is an environmental threat, as well as a valuable mycelial biomass resource. However, there is still a lack of safe and high-value conversion routes for AFR. Herein, torrefaction was applied to safely dispose of oxytetracycline fermentation residue (OFR) and simultaneously convert it into a high-performance adsorbent, and the adsorption performances of the resultant torrefaction char (TC) and pyrochar from pyrolysis were compared to show the advantage of torrefaction in converting the biomass waste into a functional adsorbent. Results showed that no oxytetracycline in OFR was detected after drying, and antibiotic resistant genes in OFR were reduced by > 6 logs after torrefaction, suggesting that torrefaction was efficient in eliminating environmental threats from OFR. Attributed to the richer oxygen- and nitrogen-containing functional groups, the TC far outperformed the pyrochar in adsorption performances at various conditions, suggesting that torrefaction was more efficient than pyrolysis for converting the biomass waste into a functional adsorbent. Specifically, the maximum adsorption amounts for uranium (U(VI)) and methylene blue (MB) by the TC reached 141 and 582 mg/g, respectively. Spectroscopic analyses evidenced that the oxygen-/nitrogen-containing groups on the TC dominated the adsorption of these pollutants. Moreover, no decreases of U(VI) and MB adsorption amounts and intensity of surface organic functional groups were observed for the TC after several cycles, suggesting the high reusability of the TC. Therefore, this study suggested that the AFR could be safely valorized via torrefaction into a powerful adsorbent for the removal of various pollutants from the solution.

Automated summary

Torrefaction was utilized to safely dispose of oxytetracycline fermentation residue and convert it into a high-performance adsorbent, with the torrefaction char demonstrating superior adsorption performances compared to pyrochar. The study suggested that torrefaction is an efficient method for converting antibiotic fermentation residue into functional adsorbents for pollutant removal.