| The accumulation of heavy metals in municipal sludge limits its value.To weaken the effectiveness and enhance the availability of heavy metals in sludge,earthworm mucus was used as an additive for sludge composting.Therefore,in this study,earthworms were first induced to produce mucus using various electric shock modes,based on the analysis of mucus components to obtain high value mucus.The high-quality mucus was then used in sludge composting in five modes: sludge composting alone,rice husk charcoal composting sludge alone,mucus composting sludge alone,combined mucus-rice husk charcoal composting sludge,and mucus-modified rice husk charcoal composting sludge,to investigate the physical and chemical properties of the sludge,heavy metals and microbial changes in the composting process,to investigate the mode of influence of sludge composting on heavy metals and microbial structure in sludge and its mechanism of action,the main findings are as follows:(1)The mucus produced by the six groups of electrical stimulation patterns mainly consists of the following main components: proteins,amino acids and carbohydrates.Among the mucus produced by different electrical stimulation,p H and conductivity were higher at 6V 20 m A,total nitrogen and total phosphorus content reached the maximum at5 V 30 m A,total potassium content reached the maximum at 6V 10 m A,protein,amino acids and carbohydrates were highest in the mucus produced at 5V 10 m A.In comparison,trace elements reached the lowest value at 5V 10 m A.The principal component analysis,combined with previous studies,revealed that the mucus produced by electrical stimulation at 5V 10 m A was weakly alkaline,high in amino acids and nutrients and low in trace metal elements,and was best suitable for sludge and straw composting experiments,soil remediation and improvement experiments.(2)The addition of mucus,mucus-rice husk charcoal and mucus-modified rice husk charcoal can increase the temperature of the pile to above 60°C for 4～6 days and reduce the water content of the sludge to below 50% after composting.When rice husk charcoal,slime rice husk charcoal and mucus-modified rice husk charcoal were added to the compost,the p H of the pile increased to 8.25～8.49,the conductivity of the composted sludge with the addition of mucus increased by 1.57% and increased the mineral salt content compared to the sludge composted alone;the organic matter degradation efficiency of the composted sludge with the addition of mucus rice husk charcoal and mucus modified rice husk charcoal was as high as 49.38% and 49.00% after composting compared to the sludge composting alone,increased by 101.56% and 102.05%,total potassium content increased by 20.16% and 16.91% compared to sludge alone,and nutrient salts were abundant;both the addition of mucus and rice husk charcoal to sludge composting increased the nutrient content of total nitrogen,total phosphorus and total potassium by 0.44%～4.03%,3.12%～20.01% and 4.39%～20.16%,respectively;the highest total phosphorus content was found with the addition of mucus and mucus-rice husk charcoal composted sludge,which increased by 11.35% and 6.20% with higher nutrient content than sludge composted alone.(3)Mucus alone was effective in reducing heavy metals Cu after composting sludge,while mucus-rice husk charcoal and mucus-modified rice husk charcoal reduced the content of heavy metals Ni,Zn and Cd in sludge;p H and TP were found to be the main factors affecting the effective states of Ni,Zn,Cd and Cu in compost by correlation analysis and stepwise regression equation,respectively.When analysing the morphology,it was observed that the Ni,Zn and Cd carbonate bound state and Fe-Mn bound state of rice husk charcoal compost alone gradually changed to Fe-Mn bound state and residual state,the Ni,Zn and Cd carbonate bound state and residual state of mucus compost alone gradually changed to Fe-Mn bound state and organic bound state,and the Ni,Zn and Cd exchangeable state,carbonate bound state and Fe-Mn bound state of mucus rice husk charcoal and mucus modified rice husk charcoal compost gradually bound state and FeMn bound state transformed into organic bound state and residue state,the addition of mucus rice husk charcoal and mucus modified rice husk charcoal were effective in passivating the effectiveness of heavy metals Ni,Zn and Cd in sludge,but revitalised Cu.Mucus-composted sludge alone was effective in passivating the efficacy of the heavy metal Cu.(4)The sequencing coverage of bacterial samples in all five treatment groups excee ded 98.6%,accurately reflecting the actual bacteria situation in the samples.The abunda nce and diversity of bacterial communities showed a gradual decrease during sludge com posting.At the phylum level,the dominant bacterial groups at the beginning of composti ng were Chloroflexi,Proteobacteria,Acidobacteria and Bacteroidetes,and the leading g roups in the stable piles at the end of composting were Firmicutes,Chloroflexi,Actinoba cteria,and at the genus level,the dominant groups at the beginning of composting were Anaerolineaceae＿uncultured,Caldilineaceae＿uncultured,Saccharibacteria＿norank,Sap rospiraceae＿uncultured,TK10＿norank.The phylum-level bacterial and physicochemica l properties and heavy metals analysis revealed that Firmicutes showed significant negat ive correlations with organic matter and total nitrogen,and significant positive correlatio ns with p H,conductivity and pile temperature,while Chloroflexi and Proteobacteria sho wed significant negative correlations with p H,conductivity,total potassium and pile tem perature,and significant positive correlations with total nitrogen and organic matter,and Actinobacteria showed significant positive correlations with total phosphorus and total potassium;The mucus-rice husk charcoal and mucus-modified rice husk charcoal compo sts had higher Firmicutes abundance and lower Chloroflexi and Proteobacteria abundan ce,and sound effect in reducing Ni and Zn effective state;rice husk charcoal and mucus-modified rice husk charcoal composts had Actinobacteria abundance at lower levels an d sound effect in reducing Cd effective state.Figure 24 Table 16 Reference 147... |
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