Effieciency And Mechanism Of The Enhancement Anaerobic Treatment Of Spectinomycin Mycelial Residues By Alkaline-thermal Pretreatment And Conductive Medium

Antibiotic pharmaceutical industry is a strategic industry related to the national economy,people’s livelihood,economic development and national security.In recent years,with the development of high quality of the pharmaceutical industry,the production of antibiotics has been increasing.Meanwhile,the suitable treatment of a large number of byproducts antibiotic mycelial residue has become a prominent problem restricting the development of the industry.Antibiotic mycelial residues produced by fermentation are classified as hazardous wastes because they contain antibiotic residues and carry antibiotic resistance genes（ARGs）.At the same time,they contain a lot of organic matter,and are also classified as perishable organic solid waste,which could be reused.Anaerobic digestion is one of the important technologies to realize the reduction,harmless and resource utilization of antibiotic mycelial residues,but its application is limited by the antibacterial activity of antibiotic,low conversion efficiency and antimicrobial resistance risk of system.In this paper,taking spectinomycin mycelial residue（SMRs）as a representative,the efficiency and mechanism of alkaline-thermal pretreatment and conductive medium to enhance the anaerobic digestion performance of SMRs were explored.The antimicrobial resistance risk of the treatment process was analyzed,and the environmental benefits were preliminarily analyzed,thus providing theoretical reference and technical support for an efficient and safe utilization of SMRs.The effects of alkaline-thermal pretreatment techniques on mycelium decomposition,organic matter dissolution,biomethane potential,antibiotics and ARGs reduction were investigated.The results showed that the synergy of alkali and heat could effectively promote the decomposition of bio-flocs and mycelium,organic matter solubilization and hydrolysis of macromolecular organic matter,and mineralization was not occurred in the pretreated system（VS biomass loss of 0.3%～0.8%）.Excessive temperature（140 ^oC）and p H（13）will make the system produce a large number of organic matter which is not easy to biodegrade,thus reducing the biomethane potential of SMRs.Alkaline-thermal pretreatment can remove spectinomycin efficiently.The degradation mechanism of spectinomycin during the pretreatment process was studied by density functional theory and transition state theory.It was concluded that the efficient degradation of spectinomycin was attributed to the general base-catalyzed hydrolysis reaction.Alkaline-thermal pretreatment can also reduce the abundance of ARGs.Through the change of spectinomycin and ARGs and biomethane potential,the suitable parameters were determined as 90 ^oC,p H 12 and 2 h.Under the operating conditions,the methane production increased from 230.0±5.4 m L（g VS）^-1 in the untreated group to 267.1±5.0m L（g VS）^-1.The spectinomycin residues decreased below the detection of limit(16.5μg kg^-1).Therefore,alkaline-thermal pretreatment can enhance the biomethane potential of SMRs by removing the bacteriostatic effect of spectinomycin and increasing the content of soluble available substrates.A stable and efficient semi-continuous flow anaerobic digestion of SMRs was established by adjusting the operation conditions and adding conductive medium（activated carbon or Fe₃O₄nano particles,NPs）.The changes of methane yield,biogas purity,reduction ratio,microbial community structure and metabolic pathway under different operation strategies were analyzed.Spectinomycin and ammonia nitrogen inhibition can be produced in the system in a long-term anaerobic digestion of SMRs.Alkaline-thermal pretreatment can eliminate the inhibition effect of spectinomycin,and coarse starch can adjust the C/N ratio of feedings to eliminate the inhibition of ammonia nitrogen,thus ensuring the stability of a long-term operation.The operating system can effectively resist the impact of organic load.When the organic load rate in the system was set to 3.056 g VS（L·d）^-1,the maximum daily methane production under experimental conditions was 336.98±14.45 m L g VS¹,and the maximum TS removal rate was 70.10±1.18%.The addition of 500 mg g VS^-1 activated carbon or 50 mg g VS^-1 Fe₃O₄NPs can significantly improve the methane yield,biogas purity and reduction effect of anaerobic digestion system,and reduce the content of inhibitory substances.When the organic load rate in the system was set to 3.056 g VS（L·d）^-1,the average daily methane production in the experimental group with activated carbon or Fe₃O₄NPs increased by 11.36%and6.78%,and the removal rate of TS increased by 5.09%and 2.85%,respectively.The proportion of methane in biogas increased from 67.52%in control group to 72.02%in the experimental group with activated carbon and 70.57%in the experimental group with Fe₃O₄NPs,respectively.The hydrolytic acidification metabolic processes were enhanced due to the addition of conductive medium,and Methanobacterium and Candidatus＿Methanofastidiosum were enriched.The efficiency of CO₂ reduction and H₂-dependent methyl-reductive methanogenesis process was improved by improving the efficiency of electron transport and related functional enzyme activities.Based on the biological characteristics of spectinomycin degradation products and the variation of ARGs abundance during the treatment process,the safety of treatment process was investigated.The antibacterial activities and toxicities of the degradation products are significantly lower than those of the parent,and the product is biodegradable,thus reducing the negative effects on the environment.In the pretreatment-anaerobic digestion process,the abundance of ARGs were reduced by 0.62 orders of magnitude.The abundance of ARGs and mobile genetic elements（MGEs）in the effluent of the reactor was effectively reduced,while their abundance in the sludge of the reactor without the addition of conductive medium was increased.The abundance of ARGs and MGEs in the reactor with conductive medium was lower than that of inoculums.Meanwhile,due to the change of microbial community,the VGT potential and conjugation and transformation potential of HGT were lower in the system with conductive medium,thus improving the safety of the resource utilization of SMRs.The carbon emission reduction benefits of direct drying and incineration were compared with those of two treatment routes including alkaline-thermal pretreatment combined anaerobic digestion with conductive medium-drying and incineration or land utilization.The carbon emission of direct drying and incineration of 1t SMRs（water content of 87.3%）was 48.66 kg CO₂.However,the treatment routes related to alkaline-thermal pretreatment combined anaerobic digestion with conductive medium can effectively reduce the carbon emission.Taken drying and incineration as terminal disposal can reduce carbon emissions by 42.2%～51.4%.Taken land utilization as terminal disposal can reduced carbon emissions by 54.7%～62.8%.Two treatment routes including alkaline-thermal pretreatment combined anaerobic digestion with conductive medium-drying and incineration or land utilization,can efficiently and safely realize harmless,resource utilization and reduction of SMRs,and contribute to the development of reducing pollution and carbon emission.