Biodegradation of Chlortetracycline by Trametes versicolor –Produced Laccase: By-Product Identification

Chlortetracycline (CTC) is one of the widely used antibiotics in animal farms commonly found in wastewater and surface water and therefore development of new treatment technologies is necessary to avoid adverse effects on humans and the environment. White-rot fungi laccase is an attractive candidate for safe treatment of water and wastewater contaminated with micropollutants. In this work, Trametes versicolor laccase was produced and response surface methodology with a central composite design was employed to investigate the effects of different parameters including pH, temperature, mediator concentration, and enzyme concentration on biodegradation of CTC in the aqueous phase. A quadratic model was fitted to express the effects of each parameter including quadratic, linear, and interaction terms. The values for R2 and adjusted R2 were 0.85 and 0.70, respectively, indicating a reasonably good model for practical applications. Among the examined parameters, linear terms of temperature and pH had the largest effects. It was observed that the maximum degradation efficiency of approximately 95% can be achieved at pH, temperature, enzyme concentration, and mediator concentration of 5.2, 35.5°C, 62.3 units/L, and 10.9 μM, respectively. Also, three structures were proposed for the by-products of CTC biodegradation using mass spectroscopy data, and the yeast estrogen screen test showed that these by-products are not toxic.