Characterization Of Bacterial Community Of Hyperthermophilic Composting And Its Application On The Removal Of Antibiotic Resistance Genes

The number of sewage treatment plants has been increasing recent years with the rapid process of urbanization in China.As a result,the amount of sewage sludge is rising substantially.The sewage sludge contains heavy metals,antibiotic,antibiotic resistance genes and parasitic ovum and other harmful materials,which imposes possible risks on public health.On the other hand,the sewage sludge is also an important renewable resource rich in various nutrients and high organic matter needed for plant growth,which can be used for potential resources.Therefore,how to dispose the sludge harmlessly and further recyle the sludge are important issues for urban sustainable development.Thermophilic composting is one of the methods in the treatment of sewage sludge to realize sludge recycling.However,the traditional thermophilic composting has some disadvantages,such as long fermentation,low efficiency,and unthorough harmless,especially in removing antibiotic resistance genes(ARGs)and mobile genetic elements(MGEs).Recently,there is a novel and effective hyperthermophilic composting technique,in which the fermentation temperature can reach more than 90 ? without exogenous heating,20-30 ? higher than traditional composting.This unique composting technique has a higher bioconversion efficiency and lower cost compared with traditional composting.But whether the hyperthermophilic composting is powerful for removing the ARGs,MGEs and functional microbial communities is still unclear.In this study,full-scale experiments were conducted in Shunyi Sludge Resource Treatment Plant,Beijing using local municipal dehydrated sludge to investigate the physicochemical composting properties,ARGs and MGEs abundance,and potential hosts via hyperthermophilic and conventional composting methods.We hypothesized that hyperthermophilic composting(a)has distinctive composting properties and microbial community composition;(b)can effectively reduce the abundance of ARGs and MGEs compared with conventional composting;(c)extreme-high temperature and associated with abating of sludge-borne microbial population and communities are the main factors to the removal of the ARGs and MGEs.The result of physicochemical properties of hyperthermophilic composting and conventional composting showed that hyperthermophilic composting can accelerate the process of sludge compost maturity and shorten fermentation period than conventional composting.The physicochemical properties of hyperthermophilic composting were similar to conventional composting.Germination index of hyperthermophilic composting was 89.9%by day 21 that higher than conventional composting.It showed that hyperthermophilic composting can quickly complete the composting process and humification.Hyperthermophilic composting could not only improve the efficiency of composting,but also improve the quality of the compost products.Illumina high-throughput sequencing bacterial 16S rRNA gene was used to determine the structure and composition of bacterial communities in the two composting processes.The results showed that hyperthermophilic composting has different bacterial community structure and composition compared to conventional composting.The bacterial communities in the initial stage of two compost treatments were mainly Proteobacteria and Bacteroides.Hyperthermophilic composting significantly reduced the relative abundance of Proteobacteria and Bacteroidetes from 32.1%to 2.0%and 30.6%to 0.32%by day 15,respectively.Correspondingly,the abundance of thermophilic phyla,Thermi and Firmicutes,increased from 0.41%to 53.1%and from 8.0%to 42.3%by day 15,respectively.During the thermophilic composting,Proteobacteria,Bacteroidetes,Firmicutes and Actinobacteria were the mainly bacterial taxa.Real-time fluorescent quantitative PCR was used to determine the abundance of ARGs and MGEs in two composting treatments.The ARGs removal efficiency and its removal mechanisms in two composting methods also were analyzed.The results showed that hyperthermophilic composting accelerates the removal of ARGs and MGEs(89%and 49%respectively)in sewage sludge.Compared to conventional composting,hyperthermophilic composting can effectively shorten the half-life of ARGs and MGEs(67%and 58%respectively)and accelerates the removal efficiencies of them.Partial Least-squares Path Modeling(PLS-PM)showed that the abundance of MGEs played a key role in the removal of ARGs of hyperthermophilic composting,while the decrease of ARGs in conventional composting was mainly affected by the change of bacterial community.