Study On The Evolution Characteristics Of Organic Matter In Mixed Compost Of Different Conditioners And Bioleaching Dehydrated Sludge

Composting of sludge and agricultural and forestry wastes can improve the stability of organic carbon in the soil,reduce part of CO₂ emissions,and promote“carbon neutralization”.Dissolved organic matter（DOM）is the most active part of organic matter transformation in the composting process,and the organic matter is degraded into stable humus-like substances（HS）.It is of great scientific significance to study the evolution characteristics of DOM and HS for reasonably evaluating the transformation process and maturity of compost organic matter.In this study,Bioleaching deep dewatered sludge was used as the main material,and four kinds of agricultural and forestry organic wastes（bagasse,straw,rice bran and sawdust）were used as single auxiliary material for mixed composting.The structural characteristics and evolution law of component content of organic matter during composting with different auxiliary materials were explored.DOM and the main components of HS（humic acid and fulvic acid）were extracted from compost samples.Ultraviolet-visible spectroscopy（UV-Vis）,Fourier transform infrared spectroscopy（FTIR）and fluorescence spectroscopy were used to characterize the change of chemical structure of organic matter in compost.The content changes of DOM,HS,humic acid（HA）and fulvic acid（FA）components in composting process were determined.Finally,it analyzes the correlation between the structural changes of organic matter and the content changes of components,and explores the relationship between the structural evolution and the content changes.The composting experiment was divided into four treatment groups:T1:sludge+bagasse,T2:sludge+straw,T3:sludge+rice bran,T4:sludge+sawdust.The results showed the time sequence of maintaining high temperature period was T2>T3>T4>T1,The generated heat and microbial self-consumption reduce the water content,After composting,the p H value was stable between 7.5 and 8.5,and the final p H value of T3 and T4 treatment groups was higher than that of T1 and T2 treatment groups.The electrical conductivity of the four treatment groups was always kept in a suitable range which was harmless to plants,and the electrical conductivity of T2 treatment group kept a high value.Spectroscopic analysis of DOM,HA and FA shows that the humification degree of T3 and T4 was greater than that of T1 and T2.Proteins,polysaccharides,fats and carbohydrates are decomposed during composting,forming humus with deep aromatization.Combined with PARAFAC model to analyze 3D-EEM,the humification degree of the four treatment groups was T4>T3>T2>T1,the intensity of humus-like fluorescence peak of emission spectrum after composting was T3>T4>T1>T2,and the intensity of humus-like fluorescence peak of synchronous spectrum was T3>T4>T2>T1.At the end of composting,DOM content was T1>T2>T3>T4,while HS and FA content decreased gradually.the total amount of HS was T1>T2>T3>T4,and FA content was T2>T1>T3>T4.Organic matter was gradually transformed into stable humus-like substances during composting.Correlation analysis showed that there was a significant correlation between the content trends of DOM,HA and FA components and their spectral structure parameters,and the content and structure changed dynamically at the same time.In the four treatment groups,the correlation degree between DOM and structural parameters was T2>T1>T3>T4,and the correlation degree between HS and structural parameters was T3>T4>T1>T2.Polysaccharides,aliphatic and proteinoid substances decreased,carbonyl,carboxyl and hydroxyl groups on aromatic ring increased,and organic matter structure gradually became aromatized.According to comprehensive analysis,the stability of organic carbon after composting was improved,and carbon emissions were reduced.When rice bran and sawdust are used as auxiliary materials,the compost maturity was better,followed by straw and bagasse.