Study On The Efficiency And Mechanism Of Modified Biochar In Adsorbing Organic Matter In Water

Aiming at the defects of unsatisfactory adsorption performance,high cost,complex preparation method and poor stability of existing adsorbents,a new type of iron nitrogen with excellent adsorption performance,low cost,simple preparation route and strong reusability was developed.Co-doped biochar material（Fe-N-C）was used as an adsorbent for organic pollutants.The adsorption efficiency and adsorption mechanism of organic pollutants were systematically studied,and the new adsorbent was applied to the second sewage treatment plant.The removal of dissolved organic matter（DOM）in secondary effluent is expected to provide new ideas for the development of new adsorption technologies.The main research results of this paper are as follows:（1）Iron-nitrogen co-doped biochar（Fe-N-C）was prepared from wood chips,dicyandiamide and ferric chloride as raw materials,and the adsorption capacity and adsorption rate of the modified biochar were significantly improved.The results showed that the maximum adsorption capacity of Fe-N-C for bisphenol A（BPA）was 54 mg/g,which was significantly better than that of graphene（19 mg/g）and conventional activated carbon（6 mg/g）;The maximum adsorption capacities of eight common organic pollutants such as phenol,sulfamethoxazole,ibuprofen,carbamazepine,tetracycline,naproxen and ciprofloxacin were also much higher than those of pure biochar,conventional activated carbon and graphene;Through adsorption-desorption cycle experiments,it was verified that heat treatment can effectively restore the adsorption capacity of Fe-N-Cs,indicating that its regeneration performance and reusability are good.（2）The effects of key process parameters including organic pollutant concentration,adsorbent dosage,initial solution pH value,inorganic anions,humus and actual water body on Fe-N-C adsorption performance were investigated.The results show that the adsorption performance of Fe-N-C is almost not affected by the initial pH value of the solution;the removal rate of BPA by Fe-N-C increases with the increase of the amount of adsorbent and decreases with the increase of the initial concentration of BPA.The correlation between adsorbent dosage and BPA initial concentration showed that BPA removal rate and adsorbent dosage were positively correlated（R²=0.9674）,and BPA removal rate and BPA initial concentration were negatively correlated（R²=0.7909）,indicating that BPA in Fe-N-C the adsorption rate depends on the number of adsorption sites rather than the BPA concentration in the solution;inorganic anions and humic substances have a weak inhibitory effect on the BPA removal rate;when the actual secondary effluent is the background water quality,the adsorbent not only It still has good removal capacity for BPA,and also has good adsorption effect on dissolved organic matter in secondary effluent.（3）Through the adsorption kinetics,adsorption isotherm and adsorption thermodynamic model,combined with Raman spectroscopy analysis,BET specific surface area and pore size analysis,X-ray photoelectron spectroscopy analysis and Zeta potential analysis and other characterization methods,as well as the degree of graphitization of the material（The correlation analysis method of I_D/I_G）,specific surface area（SSA）,chemical composition and adsorption capacity explained the reaction mechanism of Fe-N-C adsorption of organic pollutants.The graphitic N and Fe-Nx coordination bonds are the main active sites promoting its adsorption performance due to the strongπ-πelectron donor-acceptor interaction with pollutants.（4）In order to further verify the practical application effect of Fe-N-C,a Fe-N-C fixed-bed adsorption device was constructed to evaluate its adsorption effect on the dissolved organic matter in the secondary effluent of the sewage plant.The results show that Fe-N-C has outstanding adsorption performance for the secondary effluent DOM.When the dosage of Fe-N-C is only 1.0 g/L,the removal rates of TOC,UV₂₅₄ and UV₂₈₀are as high as 40.18%,76.92%and 78.26%,respectively.The adsorption effect is much higher than that of pure biochar and conventional activated carbon;the analysis results of three-dimensional fluorescence spectrum,molecular weight distribution and resin classification characterization show that Fe-N-C has selective adsorption for different components in the secondary effluent DOM;Fe-N-C is used as the core fixed-bed adsorption device has a maximum removal rate of 94.09%,95.65%and 97.18%for secondary effluent TOC,UV₂₅₄ and UV₂₈₀.The adsorption capacity is close to saturation when the treatment capacity reaches 620 times the bed volume.After regeneration and heat treatment,the adsorption performance is improved.Significant recovery.