| In recent years,the total annual output of municipal sludge has increased year by year.Moreover,the sludge treatment rate in China is low,and the environmental problems caused by lagging sludge treatment and disposal have become increasingly prominent.Vermicomposting is an emerging economical and environmentally friendly method of sludge disposal.This paper takes municipal dewatered sludge as the research object,using a new type of earthworm reactor for sludge vermicomposting with the best parameters and conditions and the sludge reduction effect under continuous reaction.This paper clarified the key factors affecting the sludge vermicomposting reduction effect of the earthworm reactor.In addition,a new type of earthworm reactor vermicomposting technology pilot plant with a processing capacity of 1t/d has been developed and built.(1)The study on the optimal control parameters of the new-type earthworm reactor for sludge vermicomposting shows that the optimal conditions are the use of mature vermicompost to mix the sludge,the addition rate of vermicompost is 15%,the initial sludge moisture content is 75% and the thickness of mud laying is 6 cm.The sludge reduction effect is obvious under the best operating conditions.The volume of sludge is reduced by 28.23%,the quality of sludge is reduced by 27%,the water content of sludge is reduced from 76.83% to 72.15%,and the sludge organic matter is reduced from 52.86% to 41.38.%.(2)In the process of sludge vermicomposting,the moisture loss mainly occurs during the 12-20 hours of sludge vermicomposting,followed by the 4-12 hours of vermicomposting.The lowest moisture loss occurs in the initial stage of sludge vermicomposting.Compared with the original sludge,the mechanically bound water in the vermicompost decreased by 17.7%,and the free water content increased by18.3%.3D-EEM,TGA,SEM and biological evaluation analysis show that the addition of mature vermicompost can increase the pores and gaps of the sludge,thereby increasing the oxygen content in the sludge,and improving the activity of earthworms and aerobic microorganisms.The addition of mature earthworm manure can also speed up the humification and decomposition of organic matter in the sludge during the vermicomposting process,and improve the efficiency of vermicomposting.(3)The continuous operation effect of the new-type earthworm reactor composting pilot test equipment for sludge is stable,and the water content of the sludge can be reduced to below 72% within 20 hours.The sludge treatment cost of the pilot plant is 22.6 yuan/ton,which has significant economic benefits.Material balance analysis shows that the loss of water during composting is the main reason for the reduction of sludge quality.(4)The structure and diversity of the microbial community in the sludge vermicomposting system were studied using molecular biology methods.The results showed that after adding manure vermicompost,the diversity of bacteria and fungi in the sludge increased,while the abundance of bacteria and fungi decreased.After vermicomposting,the abundance and diversity of bacteria in the sludge decreases,and the diversity of fungi increases.The dominant bacteria in sludge vermicomposting system were Proteobacteria(30.11%-40.30%),Bacteroidetes(23.05%-2.94%),Chloroflex I(22.52%-0.28%),Saccharibacteria(4.53%-17.68%),Acidobacteria(12.07%-1.27%),Actinobacteria(0.82%-10.83%),Firmicutes(1.08%-3.89%)and Verrucomicrobia(0.90%-4.49%).(5)Correlation analysis,principal component analysis and Mental text analysis were used to explore the key influencing factors of the reduction effect of sludge vermicomposting.The results show that electrical conductivity,C/N ratio,ash conten,TOC and bacterial community succession are the main environmental factors that affect the sludge reduction effect.In addition,the reproduction and development of bacteria contribute more to the reduction of organic matter during the vermicomposting process than the fungal community. |
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