| Compared with the pollution problem of live pig and dairy cattle breeding,the environmental pollution problem of poultry farming was widely concerned due to its large number and scope.Chicken manure not only had an unpleasant smell,which had a great impact on the air around the farm,but also contained antibiotics and resistance genes（ARGs）and other pollutants in chicken manure.Improper treatment of chicken manure would cause it to enter the soil and water around the farming enterprises,which indirectly harmed to human health.In this study,aimed at the problem of the abuse of antibiotics in the breeding process of layer hens that induce a large number of ARGs pollution,the effect of the ectopic fermentation system（EFS）on the treatment of layer breeding waste and the changes of microbial community at different layers in the EFS were analyzed.This research explored the degradation of chlortetracycline（CTC）and tetracycline resistance genes（TRGs）in different layers of EFS,as well as the main potential host bacteria of TRGs,and evaluated their association with environmental factors.This study provided a theoretical basis for the popularization and application of EFS on the treatment of layer breeding waste.The specific conclusions are as follows:1.The ectopic fermentation system was used for continuous dynamic treatment of laying hens breeding waste,which realized harmlessness and resource utilization of layer breeding waste and rural straw.The high temperature period of ectopic fermentation lasted for 60 d,which reached the hygienic standard for the treatment of livestock and poultry waste（>7 d）.At the end of the experiment,the EC was 3.75 m S·cm-1,which was in line with national standard for solid waste treatment(EC<9 m S·cm-1),and the average p H of the EFS in the whole experiment was ab OTU 8.0,which ensured the stable operation of the fermentation.In this study,the absorption coefficient per kilogram of fillers to layer breeding wastewater was 1.05,which was lower than that of pig breeding wastewater,and the absorption coefficient of feces from laying hens was 4.37,which was better than that from pigs.The aerobic fermentation system was mainly composed of bacteria,followed by actinomycetes,which could effectively degrade the waste of laying hens.At the end of the fermentation,the nutrient content of the EFS was in line with the NY525-2012 on the mass fraction of total nutrient and organic matter.2.High-throughput sequencing technology was used to monitor the changes of microbial community during the EFS.The results showed that the middle layer（20-30 cm）had the highest species,diversity and richness of microorganisms and the most active metabolism,which was the degradation layer of the main organic matter and cellulose.The middle layer of the EFS was mainly organic matter and cellulose degrading bacteria,and the main dominant bacteria genus were Bacillus of Firmicutes and Thermobifida of Actinomycetes.The content of anaerobe in the lower layer was higher,and the dominant bacteria genus was A4b of Chloroflexi.In this study,high temperature and the degradation of antibiotics had appreciable impact on the bacterial community structure in the EFS.The higher dispersion of the lower layer,upper layer and middle layer indicated that the moisture content also affected the microbial community distribution.3.This research explored the fate of chlortetracycline（CTC）and tetracycline resistance genes（TRGs）in different layers of EFS,as well as the main potential host bacteria of TRGs,and evaluated their association with environmental factors.The results revealed that the degradation of chlortetracycline（CTC）at different layers of EFS accorded with first-order kinetic model curve,and the degradation half-life of CTC during the overall fermentation was 4.7 days.Until the 21st day,the degradation rate of CTC at all layers had reached ab OTU 90%,and by the end of the fermentation,CTC was almost completely degraded.Overall,the degradation rate of CTC was upper layer（0-20 cm）>middle layer（20-30 cm）>lower layer（30-40 cm）.In this study,the removal rate of TRGs and integrons（int I1,int I2）at different layers of EFS reached more than 90%,and in the middle layer（20-30 cm）,the removal effect of TRGs and integrons is better than that of other layers.The int I1 and int I2 were significantly positively correlated with TRGs,and the reduction of integrons abundance prevented the horizontal transfer of TRGs.According to the network diagram analysis,the number of positive host bacteria in the middle layer were less,and the number of positive host bacteria in the lower bedding were the most,indicated that the middle layer has a better removal efficiency of TRGs.However,the FFCH7168 of the Chloroflexi is unique to the lower layer of bedding,which might be the host bacteria of TRGs and integrons,indicating the increase in host range of TRGs and integrons in the lower layer.This experiment showed that the increase in temperature would accelerate the removal of resistance genes and integrons,and the dynamic changes of microbial community diversity are the main driving factors for the changes of TRGs in the EFS. |
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