Benign treatment and resource utilization characteristics of doramectin fermentation residues

Doramectin is a commonly used antiparasitic drug. The biopharmaceutical process to produce doramectin can generate substantial amounts of doramectin fermentation residues, causing environmental risks and increasing economic burden of pharmaceutical enterprises. In the present work, the residual doramectin in the fermentation residues was removed through a low-temperature thermal treatment (LTT) method with temperatures from 160 degrees C to 220 degrees C. The degradation products of doramectin and toxicity prediction were assessed, and the impacts of LTT on bioresource properties of doramectin fermentation residues were investigated. The high efficiency for doramectin degradation was achieved by the LTT method, and reached more than 97% at 180-200 degrees C for 30 min and at 220 degrees C for 15 min. The olefin, ether and ester groups of doramectin molecule were broken during the LTT process, and higher temperature promoted the production of degradation products with smaller molecular structure. The toxicity prediction demonstrated that the LTT method could mitigate overall acute toxicity for rats of doramectin, and the toxicity of all degradation intermediates was observably reduced at 180 degrees C. All things considered, the optimal condition for disposing doramectin fermentation residues was recommended at 180 degrees C for 30 min. The results of synchrotron-based Fourier transform infrared spectroscopy revealed that LTT had little influence on organic functional groups of solid components in doramectin fermentation residues. Under the optimal operating condition of LTT, the contents of soluble total organic carbon, soluble total nitrogen and soluble polysaccharides in doramectin fermentation residues increased by 45.83%, 19.76% and 117.87%, respectively, and the formation and release of humic acid-like matters were also promoted. Generally, the LTT technology may be a promising approach to practically and safely treat doramectin fermentation residues.