Research Of Enhancing Compost Maturity Of Sewage Sludge By Hyperthermophilic Aerobic Fermentation Technology

With the rapid development of the urban sewage treatment industry in China,sewage sludge,which is a by-product of the municipal wastewater treatment plant,is also increased dramatically.Since sludge contains a lot of biodegradable organic matter,serious environmental issues will be caused if it is discharged indiscriminately before treating.Traditional aerobic fermentation technology,which is an effective approach to treat sewage sludge for its recycling,reduction and harmless,is limited in wide application due to the shortcomings such as a long fermentation period and low fermentation temperature.Recently,an innovating technology of hyperthermophilic aerobic fermentation technology has been studied by our research group in order to overcome these shortcomings.In addition,we have established the industrialization demonstration project with the capacity of 600 t·d-1 for sludge treatment.In this study,the comparative experiments between traditional aerobic fermentation(TC)and hyperthermophilic aerobic fermentation(HTC)were performed in a full-scale composting plant to investigate the differences in composting process,microbial community structures and characteristics of dissolved organic matter(DOM),which would provide theoretical basis and technical support for HTC technology.A total of 14 physico-chemical parameters such as temperature,organic matter and moisture were determined to distinguish these two processes,suggesting that there were significant differences between HTC and TC.HTC could run at the hyperthermophilic phase of ≥80 ℃with the maximum value of 93.4℃ on day 3,and maintained for 9 days.The thermophilic phases of ≥50℃ lasted 21 d,which could promote the degradation of organic matter and enhance compost maturity.At the end of the composting process,the organic matter and total nitrogen contents in HTC were decreased by 21.2%and 11.6%,respectively,while were decreased by 15.9%and 19.5%for TC,respectively.The GI in HTC increased to 102.7%,while it only increased to 65.4%by the end of TC.These observations revealed that HTC could improve the composting temperature,speed up the degradation of organic matter and enhance compost maturity,which resulted in higher composting efficiency and shorter the composting period compared to TC,showing incomparable techno-economic advantages.16S rRNA gene high-throughput sequencing technique was used to reveal the dynamic variations of microbial community structures,and canonical correspondence analysis(CCA)was performed to identify the relationship between physico-chemical parameters and microbial community structure during composting.Results showed thatthat drastic changes of bacterial community occurred during HTC,where Thermaceae(28.0-53.3%)and Thermoactinomycetaceae(4.0-36.1%)were the dominant families in the hyperthermophilic and thermophilic phases.Canonical correspondence analysis suggested that these dominated thermophilic bacteria could be the cause of continuous high temperature in HTC,and therefore,speed up the degradation of organic matter and enhance compost maturity.The parameters of GI,pH,NH4+-N also had significant correlation with microbial communities in mature composts,which demonstrated that composts in HTC became mature after 24 days of composting.Based on Spectroscopic indicators of Ultraviolet-visible(UV-Vis),Fourier transform infrared(FTIR)and three-dimensional excitation and emission matrix(3D-EEM)spectra,the differences in DOM structures between HTC and TC were characterized.Compared with TC,9 UV-Vis spectral indexes(E253/E203,SUVA280,A240-400 and et al)varied significantly in 0-24 d,which showed that the degree of aromatization and humification of DOM increased significantly during HTC.At the end of the composting process,the results of FTIR results suggested that the contents in decreasing polysaccharide,aliphatic and amide,and increasing aromatic structures in HTC was greater than those in TC.3D-EEM spectra combined with fluorescence regional integration(FRI)analysis pointed out that the protein substance of DOM was almost completely degradated in 0-6 d by HTC,while a large amount of humic acid and fulvic acid substances were produced in 0-24 d,which suggested that compost maturity was achieved in the thermophilic phase of HTC.Parallel factor(PARAFAC)analysis further indicated that HTC could not only shorten composting time,but also improve the quality of compos.Together these results of spectral characterizations in DOM,physico-chemical parameters and microbial community structures suggested that HTC could obviously accelerate the composting process and enhance composting efficiency,showing a great application potential for recycling of organic solid waste.