The Impacts Of Earthworm Mucus And Digestion On Sewage Sludge's Microbial Community Structure

With the improvement of sewage treatment,along with sewage sludge disposal.It is common for our country to pay attention to sewage but make light of sludge.The goal that “13th plan” drown up is still outland.Vermicompost,a green environmental sludge disposal technology,comformed to the goal of “green mountains are gold mountains” and step into the public eye in recent years.Earthworms can accelerate the degradation of organic matter in sludge and promote the transformation of toxic and harmful substances.Vermicompost is a system where earthworms and microorganisms play a synergistic role,and earthworms can affect microorganisms,thereby affecting sludge treatment.The previous studies of our group investigated the comprehensive effects of earthworms on urban sludge,The comprehensive effects of earthworms include mucus and digestion.However,the effects of earthworm's mucus and digestion on sludge is unclear.If the effects of earthworm mucus and digestion on urban microbial community structure in urban sludge are ignored,it is difficult to fully explain the earthworms effects on microorganisms during the stabilization of urban sludge.This study mainly explored the effects of earthworm digestion and mucus on the physical and chemical properties and microbial community structure of sludge.In the earthworm digestion part,the effects of earthworm digestion on the microbial community structure of sludge were investigated by comparing the physical and chemical properties of the sludge group and the cast group,microbiological microscopy,and high-throughput sequencing.The physical and chemical properties of the sludge group,the mucus group and the earthworm group were compared,and the effect of earthworm mucus on sludge and the role of earthworm mucus in the earthworm composting system were explored by principal component analysis.The end result is shown below:(1)Earthworm digestion can significantly reduce the content of organic matter in sludge.Organic matter is reduced by 70.76 % after earthworm digestion.The content of ammonia nitrogen in the cast group was 6.0 times that of the sludge group,indicating that the digestion of earthworms can promote the mineralization of organic nitrogen in the sludge.Earthworm digestion significantly reduced the total nitrogen content in the sludge without significantly affecting nitrate and nitrogen.The higher conductivity of the sludge group than the cast group may be caused by the use of inorganic salts in the sludge by microorganisms in the intestinal tract of the earthworm.There was no significant difference in the available phosphorus in the sludge group and the cast group,indicating that the digestion of earthworms was not the cause of the increase in available phosphorus in the earthworm composting system.The microscopic examination of micro-animals showed that the digestion of earthworms had little effect on the composition of micro-animals,but it could significantly reduce the number of surface insects,sand-worms,rotifers and rotifer eggs in the sludge.(2)High-throughput results indicate that the sludge has decreased its richness and diversity after passing through the intestinal tract of the earthworm.Seven phylums disappeared in the 18 s rRNA gene sequence after worming by earthworms,accounting for 46.67 % of the 18 s rRNA gene sequence in the sludge.There are only 6 mycoplasmas in the 16 s rRNA gene sequence,accounting for 23.08 % of the 16 s rRNA gene sequence in the sludge,and a new mycoplasma-mena.This shows that the effect of earthworm phagocytosis on the 18 s rRNA gene sequence in sludge is greater than the 16 s r RNA gene sequence.At the level of phylum classification,earthworm phagocytosis will also have a greater impact on the proportion of microorganisms in sludge(physical level,genera level).Among the 16 s rRNA gene sequences,the mycophyta showing significant differences are Proteobacteria,Bacteroides,Fusobacteria,Actinomyces and Pachyphyta.Among them,Proteobacteria and Bacteroides decreased;18s rRNA gene sequence had significant differences in Ascomycota,Basidiomycota,and norank_k_Fungi.Among them,Ascomycota decreased significantly,and Basidiomycota and norank_k_Fungi increased.At the level of 16 s rRNA gene sequence,the bacterial genera that are relatively high in sludge are Trichomonas,Fibrobacteriaceae,Dechloromonas,Flavobacterium,all of which are The bacteria related to denitrification indicate that the phagocytosis of earthworms can reduce the abundance of denitrifying bacteria.Trichosporon,Galactomyces,norank_p__Ascomycota,and norank_k__Fungi are the main genus in vermicompost in the 18 s rRNA gene sequence.The proportion of Trichosporon and Galactomyces increased after phagocytosis by earthworms,indicating that earthworm feces can accelerate cellulose degradation in sludge.From the perspective of gene sequence function,phagocytosis by earthworms will not affect the functional composition of microorganisms in sludge,but only the abundance of functional genes.Earthworm phagocytosis reduces functional memory abundance of related amino acids,carbohydrate transport and metabolism in sludge.(3)The earthworm mucus experiment results showed that the three groups of earthworms had the fastest degradation of organic matter,followed by the mucus group,the sludge group was the slowest,and the mucus and sludge groups showed similar trends.The dosing of mucus accelerates the degradation of sludge organic matter in the early stage of the experiment and has a smaller effect in the later stage of the experiment.This is due to the utilization of the mucus by microorganisms and the volatility of the mucus.During the experiment,the electric conductivity of the mucus group was higher than that of the sludge group and lower than that of the earthworm group,indicating that the mucus increased the mineralization of the urban sludge and the mineralization of the sludge was less than that of the earthworm.At the end of the experiment,the ammonia nitrogen of the mucus group was significantly higher than that of the sludge group,indicating that the ammoniation process of the mucus is ahead of time,and the effect of the dosing of mucus on nitrate nitrogen and TN is small.On the twentieth day of the experiment,the available phosphorus in the mucus group began to accumulate and was significantly higher than that in the sludge group but lagging behind the earthworm group,indicating that mucus is one of the reasons for the increase in available phosphorus in the earthworm compost system.Principal component analysis showed that OM,pH,ammonia nitrogen,AP,and EC had higher correlations with the first principal component;SWC,TN,and nitrate nitrogen had higher correlations with the second principal component.The distribution of the samples in the principal component analysis chart shows that the similarity between the sludge group and the mucus group is higher,while the differences between the sludge group,the mucus group and the earthworm group are greater.