| With the rapid development of China’s economy,the number of sewage treatment plants has also increased rapidly.Dewatered sludge as a by-product of sewage treatment is also increasing sharply,and its disposal has become a problem for China’s environmental protection industry.In recent years,vermicomposting has developed well as a simple and environmentally friendly sludge treatment technology.Vermicomposting can reduce,stabilize and recycle sludge.However,vermicomposting has a slower stabilizing efficiency,and its products contain a large amount of pollutants such as antibiotic resistance genes,which hinders the development of its technology.Biochars can accelerate the degradation of organic matter and reduce pollutants in the environment,but its function in vermicomposting is rarely reported.Therefore,this study investigated the effects of biochars on the degradation of organic matter and antibiotics and resistance genes in sludge vermicomposting by adding 1.25% and 5% corncob biochars and rice husk biochars to the sludge,respectively.Short-term digestion experiments analyze its effect mechanism,the main results are as follows.(1)Compared with the control group without added biochar,the electrical conductivity and organic matter loss of the high-content corncob biochar group increased by 1.1 and 2.6 times,respectively;the abundance of bacteria and fungi increased by 2.13 and 11.8 times,respectively(P<0.05);Shannon index of bacteria increased by 6.8 %,and β diversity also changed significantly.This shows that high content of corncob can change the community structure and diversity of the sludge and earthworm compost by increasing the number of bacteria and fungi in the sludge and vermicomposting,and improve the efficiency of vermicomposting.Compared with non-addition,rice husk biochar had no significant effect on the degree of mineralization and organic matter loss during vermicomposting(P>0.05);high and low concentrations of rice husk biochar had no Significant effect on the number of bacteria in sludge earthworm manure(P>0.05),but high and low concentrations of rice husk biochar significantly increased the number of fungi by 1.6 and 2.4 times(P<0.05);high content of rice husk biochar increased the Shannon index of bacteria by 4.4%,but β diversity No significant change.This shows that only high content of rice husk biochar will cause changes in the bacterial diversity in the sludge and vermicompost products,but have little effect on the degradation of organic matter and bacterial community structure.(2)Compared with the control,the average removal efficiency of the addition of biochar to tetracycline,norfloxacin,enrofloxacin and sulfonamide reached 100%,90%,50% and 20%,respectively.This indicates that biochar can promote the degradation of antibiotics during sludge and vermicomposting.The addition of corncob biochar increased the gene abundance of intI-1,sul-1 and sul-2,but had inhibitory effects on ermF and tetX genes,and had a negative correlation with corncob biochar concentration.However,the reduction of rice husk biochar resistance genes had no promoting effect.This shows that biochar is selective for degradation of resistance genes,depending on the type and concentration of biochar.(3)Compared with no addition,corncob biochar significantly increased the bacterial abundance in earthworm intestine and excreted feces by 1.4 and 2.5 times,and the fungal abundance increased by 1,200 and 7 times,respectively(P<0.05);for rice husk biochar,increased the bacterial abundance in earthworm feces by 2.35 times(P <0.05),but at the same time the bacterial abundance in the intestinal tract of earthworms decreased by 0.5 times(P<0.05).In addition,the addition of biochar led to an increase in Shannon and Simpson indices of 1.03-1.04 times and 1.08-1.19 times in the intestines and feces of earthworms.And the β diversity of bacteria has also changed.Redundant analysis showed that biochar could increase the community abundance of bacteria in the intestine of earthworms,and thus significantly increase the abundance of resistance genes in the intestine of earthworms(P<0.05).In summary,the addition of biochar can accelerate the degradation of organic matter and improve the efficiency of earthworm composting.At the same time,it has a significant removal effect on antibiotics.But the effects of antibiotic resistance genes are selective.Earthworm intestinal digestion analysis showed that biochar affected the diversity of intestinal microflora and then the fate of resistance genes. |
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