Application of the biogas residue of anaerobic co-digestion of gentamicin mycelial residues and wheat straw as soil amendment: Focus on nutrients supply, soil enzyme activities and antibiotic resistance genes

The dewatering performance of streptomycin mycelial residue promoted by the Fenton process synergistic with biochar

In this study, the performance and mechanism of streptomycin mycelial residue (SMR) dewatered by the Fenton process coupled with biochar was investigated. The optimal dosages of Fe2+, H2O2, and biochar were determined based on the response surface method (RSM), and the corresponding prediction equation was proposed. The walnut shell biochar prepared at 300 °C (WS300) exhibited the best dewatering performance due to its rough surface and large pore size. At the dosage of 0.3 g/g dry solids (DS) for WS300, the combination with Fenton process decreased the specific resistance to filtration of SMR and the water content (WC) of the filter cake by 93.9% and 27.8%, respectively. The RSM results suggested that the interaction between Fe2+ and H2O2 had significant influence on the dewatering properties compared to the other factor combinations. The optimum dosages of Fe2+, H2O2, and WS300 were 56.5 mg/g DS, 63.2 mg/g DS and 0.28 g/g DS, respectively. The strong oxidation of Fenton's reagents increased the zeta potential and reduced the particle size of SMR flocs, which promoted the release of bound water. In addition, the biochar worked as skeleton builder was conducive to construct hydrophobic channels and reduce the hydrophilicity of proteins and polysaccharides.

Characteristics of acidic hydrothermal treatment for disintegration of spiramycin fermentation residue and degradation of residual antibiotics

To recycle the nutrients in spiramycin (SPM) fermentation residue (SFR) through biological methods, acid hydrothermal treatment (AHT) was employed as pretreatment to enhance SFR biodegradability. The results showed that the degradation rate of residual SPM in SFR reached 100% after 120 min at 100℃ and 0.30 M acid with a 30.5% and 89.7% increase in proteins and polysaccharides, respectively. The SPM degradation was faster at higher acidity and temperature. However, elevated SPM concentration and the presence of protein, humic acid, and polysaccharide inhibited SPM degradation. The disintegration of SFR was evidenced by changes in its microstructure and could be predicted through the release of dissolved organic matter. Eight major SPM intermediates were identified with lower mutagenicity and antibacterial activity testing against Staphylococcus aureus. These results demonstrate that AHT not only disintegrates SFR but also degrades the residual SPM antibiotics, which implies the possibility for practical applications.

Safe utilization of bioresources in gentamicin mycelial residues by thermal treatment: Antibiotic degradation, resistance gene inactivation and available nutrients promotion

Gentamicin mycelium residues (GMRs) abundant in organic substances were generated during the production of gentamicin. Inappropriate handling techniques not only waste valuable resources, they could also result in residual gentamicin into the natural environment, leading to the generation of antibiotic resistance genes (ARGs), which would cause a significant threat to ecological system and human health. In the present work, the effects of thermal treatment on the removal of residual gentamicin in GMRs, as well as the changes of associated ARGs abundance, antimicrobial activity and bioresources properties were investigated. The results indicated that the hazards of GMRs was significantly reduced through thermal treatment. The degradation rate of residual gentamicin in GMRs reached 100 %, the total abundance of gentamicin resistance genes declined from 8.20 to 1.14 × 10-5 and the antibacterial activity of the decomposition products of GMRs on Vibrio fischeri was markedly reduced at 200 °C for 120 min. Additionally, the thermal treatment remarkably influenced the bioresource properties of GMRs-decomposition products. The release of soluble organic matters including soluble carbohydrates and soluble proteins have been enhanced in GMRs, while excessively high temperatures could lead to a reduction of nutrient substances. Generally, thermal treatment technology was a promising strategy for synergistic reducing hazards and utilizing bioresources of GMRs.