| In this paper,aerobic composting was carried out by using dewatered sludge from sewage treatment plant in Jinnan district of Tianjin,leaves and sawdust as compost raw materials.Through the aerobic composting treatment,the biodegradable organic matter in sludge can be transformed into stable humus,using maturity compost to extract fulvic acid(FA)can not only solve the problem of source depletion of fulvic acid,but also solve the trouble of sludge disposal.The main research object of this paper is fulvic acid in sludge compost.Extraction,purification,analysis and characterization of fulvic acid from sludge compost are the main work.The details of the study are as follows:The extraction experiments of FA from sludge compost were carried out.The results show that compost grinding is beneficial to the extraction of FA;the extraction efficiency of FA by hydrochloric acid or nitric acid are similar,and the extraction efficiency with sulfuric acid is poor;nitrogen protection has no significant effect on the extraction rate of FA;the extraction rate of FA with hydrochloric acid increases first and then decreases with the decrease of solid-liquid ratio;the extraction rate of FA increases with the increase of reaction time,the increase of reaction temperature and the increase of acid concentration.Based on the orthogonal experiment of FA extraction,the factors influenced the FA extraction rate are ranked in the following order: reaction temperature > concentration of hydrochloric acid > solid-liquid ratio > reaction time.Based on the FA extraction experimental data,a mathematical model of FA extraction efficiency was established by using nonlinear optimization techniques.The statistical analysis of the model proved that this model is well posed,the average relative error of model regression is about 11.6%,and the model parameters indicated that the apparent activation energy of FA extraction reaction is about 18095 J/mol.In this paper,the purification method of crude FA by membrane dialysis,macroporous resin adsorption,nanofiltration(NF)and water washing were studied,and the samples were analyzed and characterized.When the solution temperature are 20 ?,30 ?and 40 ?,the solubility of FA purified by membrane dialysis in the water are 0.049 g/g,0.062 g/g and 0.074 g/g respectively,and the solubility of FA purified by resin in formic acid are 0.217 g/g,0.229 g/g and 0.241 g/g respectively.The total acid group content is 9-11 mmol·g-1,and the carboxyl content accounts for about 60-70% of the total acid group.Compared with the raw FA,the content of organic elemental(C,H,N,S and O)obtained with macroporous resin adsorption or nanofiltration are largely increased.The contents of organic elements in the former are more than 92.59%,while the content of Cl and Fe are about 4% and 2.76% respectively,and the content of organic elements in the latter are more than 99.52%,the contents of other elements are very low.A large amount of Cl,Fe,Ca,P and Si is contained in the water washing sample.It is clear that the NF purification method is more thorough and efficient.The elemental analysis of membrane classification samples showed that the C/N of low molecular weight was higher,while the C/H in FA for different fractions are similar,the value is about 0.53.The infrared spectrums show a large number of carboxyl groups,hydroxyl groups,aliphatic structures and aromatic structures exist in FA,and FA of low molecular weight contains more oxygen functional groups.It is known from TG-DSC analysis that the weight loss of FA mainly happen in the range of 150-500 ?.The results of scanning electron microscope and X-ray powder diffraction showed that the FA in this study is an amorphous solid. |
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