Structural Analysis And Functional Study Of Fulvic-like Acid Substances Derived From Black Liquor In Papermaking Industry

Papermaking black liquor accounts for about 90% of the pollution in the whole papermaking and pulp industry.If it is directly discharged without treatment,its high p H,high biological oxygen demand(BOD)and chemical oxygen demand(COD)will cause great pollution to the environment.In addition,a large number of organic substances represented by lignin are not fully utilized,which also lead to resource waste.Moreover,lignin,cellulose,hemicellulose and other components in black liquor will generate a large number of humic acid substances due to physical and chemical reactions in the pulping process.Therefore,extracting usable humic acid from pulp black liquor can not only improve the utilization rate of waste water and be beneficial to the environment,but also realize the reuse of resources.Although there have been studies on the extraction of fulvic-like acids from black liquor in papermaking,there has been no in-depth study on the structural and functional differences of fulvic-like acids extracted under different papermaking processes.This article uses alkali method and ammonium method black liquor as materials to extract alkali method fulvic-like acid substances(JFLA)and ammonium method fulvic-like acid substances(AFLA),and compares them with the chemical structure of mineral source fulvic acid(KFA).At the same time,it verifies the complexation and passivation effects and differences of the two types of fulvic-like acid substances on heavy metals in water and soil environments,In addition,the impact of different types of fulvic-like acid substances on microbial communities in heavy metal contaminated soil was studied.1.Correlation analysis of fulvic acid application in agriculture based on bibliometricsBibliometrics analysis shows that the application of fulvic acid in agriculture is increasing;The impact of humic acid on crop yield improvement and growth,soil quality and stability,adsorption and complexation ability of metal ions,and analysis of its own structure are research hotspots.2.Extraction and structural analysis of fulvic-like acid substances derived from black liquorThe AFLA content in ammonium papermaking black liquor is 70.4%,and most of the organic matter in the black liquor can be transformed into precursors of fulvic acid and extracted;The JFLA content in alkaline papermaking black liquor is 9.4%.Most of the insoluble organic matter in the black liquor is removed by centrifugation,and soluble lignin is precipitated during the acid precipitation process with a decrease in p H.A small portion of the acid soluble organic matter is extracted as a precursor of humic acid.AFLA has higher nitrogen and oxygen content than JFLA,and lower hydrogen content;JFLA has lower aromaticity and lower content of oxygen-containing functional groups than AFLA.3.Study on the adsorption and passivation of lead by fulvic-like acid substancesIn aquatic environments,the adsorption effect of fulvic-like acid substances on Pb is better at low concentrations of metal ions,and the adsorption effect is significantly influenced by p H.AFLA has better metal adsorption capacity than JFLA.In the soil environment,the passivation effect of fulvic-like acid substances on the soil is achieved by converting exchangeable and carbonate Pb ions into inactive iron manganese oxidized,organic,and residual states.JFLA has a passivation effect on heavy metals in soil,while AFLA can increase the active content of heavy metals.4.Effects of fulvic-like acid on microbial communities in lead contaminated soilAfter adding different types of fulvic-like acid substances to passivate lead contaminated soil,the OTUs of soil communities decreased to a certain extent,with the AFA group having the least decrease in OTUs and the JFA group having the most decrease in OTUs.At phylum level,it mainly affects the abundance of Proteobacteria,Actinomycetes,Bacteroides,Firmicutes and Acidobacteria in soil.The abundance of Firmicutes and Bacteroides increased,the abundance of Acidobacteria and Actinomycetes decreased,and the number of Proteobacteria increased or decreased differently;At the genus level,it mainly affects the abundance of Bacillus and Monomonas genera.The function prediction showed that the addition of fulvic acid like compounds would produce dominant strains and increase the nitrogen cycle capacity of soil microorganisms.