Degradation of tetracyclines and sulfonamides by stevensite‐ and biochar‐immobilized laccase systems and impact on residual antibiotic activity

Abstract

Abstract BACKGROUND Stevensite and biochar were investigated to covalently immobilize laccase from Myceliophthora thermophila (MtL) and Pleurotus eryngii (PeL) through the sequential application of aminopropyltriethoxysilane and glutaraldehyde. The immobilized preparations were tested to remove three tetracyclines and six sulfonamides at 0.1 mmol L −1 of each antibiotic. Degradation experiments were conducted both in the absence and in the presence (0.2 mmol L −1 ) of ABTS, 1‐hydroxybenzotriazol (HBT), syringaldehyde or violuric acid. The residual antibiotic activity was tested towards five bacterial species and a bacterial consortium from wastewater. RESULTS Higher values of activity yields (74% and 70.3%) and catalytic capabilities (1426 and 1405 IU g −1 ) were obtained with PeL on stevensite and biochar than with MtL. Stevensite enabled higher reusability and storage stability than biochar. Best removals of tetracyclines and sulfonamides were obtained with immobilized‐laccase systems coupled to ABTS or syringaldehyde. Immobilized‐laccase/ABTS systems removed 100% of tetracyclines while only chlortetracycline was completely removed in the presence of syringaldehyde. With ABTS, the most effectively removed sulfonamides were sulfathiazole and sulfadiazine (up to 100% and 54%), while syringaldehyde best supported the removal of sulfanilamide, sulfamethazine and sulfamethoxazole (up to 42%, 45% and 46%, respectively). In some cases, an effective antibiotics removal led to either low or no residual antibiotic activity. CONCLUSION MtL and PeL were immobilized successfully on biochar and stevensite. The addition of either ABTS or syringaldehyde enhanced significant removals, up to 100%, of tetracyclines and sulfonamides by the immobilized laccase systems. Noteworthy, biochar‐immobilized laccases/ABTS led to complete suppression of the antibiotic activity of tetracyclines. © 2018 Society of Chemical Industry