Characteristics and phytotoxicity assay of biochars derived from a Zn-rich antibiotic residue

Abstract:

Zn-rich antibiotic residue-derived biochars were produced at different temperatures (300-700^oC) and duration times (1 and 2 h). It was found both temperature and duration times had significant effect on the biochar’s physiochemical properties, speciation and bioavailability of Zn. The ash content and pH increased as temperature and duration time increased, whereas the biochars yield decreased with the increasing temperature. Pyrolysis process increased the biochar surface area with biochars produced at 500 ^oC showing the greatest surface area at 43.02 and 32.79 m²/g for duration times of 1 and 2 h, respectively. While a further increase in pyrolysis >500 ^oC decreased the surface area, SEM analysis showed that the biochars produced at 500 ^oC had the most developed pore structure. Zn was concentrated through pyrolysis, and the pyrolysis process stabilized Zn by transforming acid-soluble species into relatively stable forms. EDTA sodium had higher biochar Zn extraction efficiency than that of citric acid, CaCl₂ and NaOAc. The final phytotoxicity test based on plant response indicated that the application of antibiotic residue and resultant biochars had significant adverse effect on the ryegrass growth. The phytotoxicity decreased for the biochars produced with higher pyrolysis temperature and longer duration time, which reveals the stabilization of Zn during pyrolysis treatment. These results are useful for designing an environmental friendly means for disposing the Zn-rich antibiotic residue.