Effects Of Oxytetracycline And Doxycycline Antibiotics On Anaerobic Digestion Of Swine Manure

As socialism with Chinese characteristics has entered a new era,China has been promoting intensification and large-scale of the livestock farming is an inexorable trend.With the transformation and upgrading of stockbreeding,some new environmental problems arised due to livestock manure optional emissions.How to solve those problems has become an important research point for China to achieve rural revitalization.At present,direct utilization,insect transformation,composting and anaerobic digestion are common ways to use livestock manure.Anaerobic digestion is promising due to its advantages of low energy consumption,low pollution and renewable energy production.However,the high antibiotic residues in manure would affect the anaerobic digestion system.The fouces of this study is on the effect of veterinary antibiotics on anaerobic digestion.Swine manure was used as substrate in the study.Batch fermentation technology was conducted to evaluate the biogas yield and the effect of various oxytetracycline/doxycycline concentrations and different oxytetracycline and doxycycline ratio on biogas/methane yield,p H,ammonia nitrogen,COD,gas production rate,antibiotic residues,and microbial community.This study provided reference for the anaerobic digestion containing oxytetracycline and doxycycline.The results showed that the cumulative biogas/methane yield decreased gradually with the increase of oxytetracycline concentration,and it was negatively correlated with the antibiotic concentration.In the concentration range of 60～200mg·L^-1,however,the cumulative biogas/methane yield showed a positively linear relationship with the concentration.The higher the oxytetracycline and doxycycline concentration is,the lower the rate of methane production is.The experiment starting time was prolonged with doxycycline increasing.Different concentrations of oxytetracycline and doxycycline had weak effect on p H value,ammonia nitrogen content and COD in the anaerobic digestion process,but oxytetracycline has negative effects on methane production rate and the stability of the anaerobic digestion system.The inhibitory effect of oxytetracycline was greater than that of doxycycline in the combined experiment.Oxytetracycline and doxycycline were removed by biosorption and biodegradation in anaerobic digestion system.The biosorption was the main way of antibiotic removal,and the removal rate by biosorption showed that:doxycycline>oxytetracycline.The main target of biodegradation is the residual after biosorption.Moreover,the antibiotic removal by degradation conformed to the first-order kinetic model,and the half-life of oxytetracycline was much longer than that of doxycycline.In addition,the residual amount showed a positively linear correlation with the initial concentration.The results of alpha microbial community diversity analysis indicated that the doxycycline concentration at 200 mg·L^-1of microbial community diversity and evenness were seriously damaged.Microbial diversity and evenness also were adversely affected when oxytetracycline concentration was at 150 mg·L^-1in the combined experiment.The microbial community structure was changed in antibiotic environment for long time.Relative abundance of Firmicutes,Bacteroidetes and Proteobacteria decreased,but Acidobacteriota,Proteobacteria and Actinobacteriota became the dominant bacteria.Doxycycline has an effect on the stages of hydrolysis and acid-producing,which could lead to acid accumulation and reduce methane production.The results of this study provided theoretical basis and reference for the anaerobic digestion containing oxytetracycline and doxycycline in biogas project.