Performance Of Hydrothermal Treatment Of Lincomycin Mycelial Residues(LMRs) And Soil Application Safety Investigation

Antibiotic mycelial residues(AMRs)is one kind of byproducts in the process of antibiotic production.The untreated AMRs is easily re-fermented as it contains lots of water(60～90%)and organic matters.The re-fermentation will produce airpolluted oder,and also contaminate soil and groundwater.Moreover,the residual antibiotics in AMRs will induce bacterial resistance and pose environmental risks.The AMRs appeared on the hazardous material list of China in 2008,and its harmless treatment is urgent to realize for the pharmaceutical enterprises.In this research,the hydrothermal method was developed based on the characteristics of lincomycin mycelial residues(LMRs)that it is rich in organic matters and lincomycin is stable.The goals of the research is to remove residual lincomycin and lincomycin resistance genes in LMRs,and to immobilize heavy metals simultaneously.Then the treated LMRs could be used as soil amendment to enhance its fertility.This research tries to develop a harmless and resourceful treatment method for AMRs and make the theoretical foundations for the technical norm of AMRs pollution control.This study firstly investigated the release of fertilizer-use organic matters with hydrothermal treatment and optimize lincomycin removal parameters via response surface methodology(RSM).Meanwhile,investigate lincomycin removal characteristics in hydrothermal treatment process.The results showed that the content of dissolved organic matters(polysaccharide and protein),total nitrogen and phosphorus increased significantly with the increase of reaction temperature.However,the soluble organic matters and nitrogen decreased as reaction time extended to 180 min because of consumption of Maillard reaction.The multiple regression model based on RSM predicted lincomycin removal in hydrothermal process.A degradation model was developed successfully based on the degradation kinetics analysis.According to the model,observed reaction constant(k)increased with the elevation of reaction temperature and acid concentration.Additionally,increasing initial concentration of lincomycin promoted its degradation,while it showed a different trend once the concentration exceeded 300 mg/L.Secondly,we investigated the changes of harmful factors such as lincomycin resistance genes,mobile genetic elements and heavy metals in LMRs hydrothermal treatment process.Then,the biotoxicity test was conducted to evaluate the toxicity of hydrothermal treated LMRs.The results showed that about 99% of lincomycin resistance genes and mobile genetic elements were removed after hydrothermal treatment.A two-phase first-order kinetic model was developed to display the target genes’ removal in hydrothermal treatment process.The target gene removal rate in the first stage was two orders of magnitude higher than that in the second stage(after 30 min of treatment).There was a significant correlation between the absolute abundance of lincomycin resistance genes and int I1,Tn916/1545.Moreover,the proportion of stable heavy metals(organicbounding fraction and residual fraction)increased after hydrothermal treatment,and the environmental risk decreased at least on grade based on risk assessment code evaluation.Moreover,the biotoxicity test confirmed that after hydrothermal treatment lincomycin and its degradation products have no inhibition effect to Staphylococcus aureus and Microcystis microalgae cells.A total of 7 major intermediates were identified,based on which hydrolysis,hydroxylation and desulfuration were inferred as the mainly evolution processes.Finally,the effects of treated LMRs amendment and the dose effects of lincomycin on lincomycin resistance genes and soil bacterial communities were studied.The results told that application of treated LMRs did not cause the significant increase of lincomycin resistance genes and changes of soil microbial communities structure.However,the introduced lincomycin induced the increase of lincomycin resistance genes after incubation for 8 days,and two genes(lmr A and lnu B)showed a dosage-related increase.However,the abundance of lincomycin resistance genes recovered to the control level as the incubation period extended to 50 days,indicating a low persistence in soil.In addition,alpha diversity of LMRs amended soil was lower than control soil.Chao1 and Shannon indexes were negative correlated with lincomycin concentration.In addition,LMRs application markedly shifted the bacterial composition,difference was found between control soil,10 mg/kg and 50 mg/kg lincomycin amended soil.The difference was decayed as incubation period extended to 50 days.