| The refractory dissolved organic matter(DOM)in the effluent after biochemical treatment of organic wastewater is the main object of advanced wastewater treatment.As one of the main methods for DOM removal,adsorption method has uncertainties in the adsorption efficiency of DOM in water and the selective adsorption of complex components in DOM due to the specificity of the structure and composition of different adsorbents.Gasification residue is a by-product of coal-to-gas,and there has been a lack of targeted research as DOM adsorbent material.Based on the feasibility experiment of adsorbing and removing DOM from the biochemical tail water of the tannery industry by gasification residue,this paper studied the modification of gasification residue using an acid-base synergistic microwave method,selected fulvic acid and gallic acid as the representative components of humic and polyphenolic DOM in the tannery wastewater,and explored the adsorption selectivity mechanism of modified gasification residue for refractory DOM,with a view to providing a new way for the gasification residue to "treat waste with waste".The main findings are as follows:(1)The inorganic chemical composition of the gasification fine slag is mainly 43.54%SiO2,25.29%Al2O3,and 9.52%Fe2O3.Through calculation,its activity coefficient is 0.58.The specific composition is divided into two parts:a smooth and dense silicon aluminum microsphere and a porous residual carbon structure,with a specific surface area of 348.21 m2/g.Combined with infrared data,it is shown that the surface contains carboxyl and hydroxyl functional groups.Compared with gasification fine slag,the surface of activated carbon is smooth and regularly distributed with pores,with a specific surface area of 1298.6 m2/g,which is about three times as large as that of gasification fine slag,and a pore volume of about two times as large as that of gasification fine slag.After acid base synergistic microwave modification,four types of modified gasification fine slag were selected,namely,0.5%sulfuric acid,0.5%sulfuric acid synergistic microwave,5%sulfuric acid synergistic microwave,and 50%sulfuric acid synergistic microwave modification.The characterization results showed that more densely arranged honeycomb shaped pores appeared on the surface of the modified gasification fine slag,and both the specific surface area and pore volume were improved.After 50%sulfuric acid synergistic microwave modification,the specific surface area could reach 490.14m2/g,Sulfuric acid assisted microwave modification not only increases the functional groups on the surface of gasification fine slag,but also destroys the silicon aluminum microsphere structure on the surface of gasification fine slag,achieving the purpose of pore expansion.Compared to the original gasification fine slag,the hydrophobic groups on the surface of modified gasification fine slag have increased,while the hydrophilic groups have decreased.Especially,for 0.5%sulfuric acid assisted microwave modified gasification fine slag,the surface hydrophobic groups after the collaborative microwave modification are as high as 71.89%.(2)The adsorption results of fulvic acid and gallic acid showed that under the conditions of adding 8 g/L gasification residue,adsorbing for 2 h,and initial concentration of the solution of 400 mg/L,the removal rate of fulvic acid and gallic acid from gasification fine residue was 80.25%and 84.85%,respectively;The corresponding removal rates of activated carbon are 63.45%and 94.48%,respectively;The corresponding removal rates of 0.5%sulfuric acid modified gasification fines are 83.76%and 97.80%,respectively;The corresponding removal rates of 0.5%sulfuric acid combined with microwave modified gasification fines were 92.28%and 97.66%,respectively;The corresponding removal rates of 5%sulfuric acid combined with microwave modified gasification fines were 81.31%and 98.00%,respectively;The corresponding removal rates of gasification fines modified by 50%sulfuric acid and microwave were 84.43%and 97.67%,respectively.Overall,the adsorption effect of gasification fine slag on large molecular weight fulvic acid is limited,and there are more adsorption sites for small molecular weight gallic acid.It can be seen that gasification fine slag has significant adsorption differences for different molecular sizes.Activated carbon exhibits a higher adsorption capacity for small molecules of gallic acid under the same conditions.After sulfuric acid and microwave modification,the adsorption efficiency of gasification fines for both is improved.The adsorption process is analyzed and fitted through adsorption kinetics and adsorption isotherms,and the results show that the adsorption process of activated carbon for fulvic acid and gallic acid is physical adsorption,and the adsorption form is multi-layer adsorption,The adsorption process of gasification fine slag and its modified products is chemical adsorption,and the adsorption form is monolayer adsorption.(3)After the gasification fine slag adsorbed on the biochemical tail water,the types of organic pollutants decreased,the total peak area of organic substances decreased by 59.4%,and the proportion of phenolic substances decreased by 8.82%.The removal effect of phenolic substances was significant.The removal efficiency of modified gasification fine slag for biochemical tail water is improved compared to that of raw gasification fine slag.Considering that the surface of modified gasification fine slag is rich in a large number of hydrophobic groups,a stable structure is formed between the modified gasification fine slag and hydrophobic substances that are difficult to degrade DOM due to the hydrophobic effect,thereby improving the adsorption effect.Through analysis of the water quality before and after adsorption,it was found that the biochemical tail water before adsorption contained a large amount of monocyclic aromatic compounds,phenols,aniline,polycyclic aromatic hydrocarbons,and heterocyclic compounds.After adsorption,the types of organic substituents in the biochemical tail water gradually decreased,with the main component being fatty chains,and the stability of the organic compounds gradually deteriorated.The modified gasification fine residue adsorption experiment was conducted on the biochemical tail water after stage filtration.It can be seen that after the biochemical tail water is filtered through different pore diameter filter membranes,macromolecular humic substances are trapped by the membrane,and macromolecular humic substances mainly exist in the range of more than 50 KDa.The modified gasification fine residue has a high removal rate for biochemical tail water with a molecular weight of less than 10 KDa,This indicates that the modified gasification fine slag has high selectivity for small molecular hydrophobic substances.In summary,compared to activated carbon,gasification fine slag has poor adsorption performance due to its low carbon content and small microporous structure.It is modified by sulfuric acid and microwave interaction,enriching the pore structure while loading a large number of hydrophobic groups on the surface,greatly improving the adsorption performance of gasification fine slag for small and medium-sized hydrophobic substances of refractory DOM components. |
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