Preparation And Modification Of Reed-based Biochar And Its Effect On Fixation Of PAHs In Sediment

Reed is a good precursor for the preparation of biochar because of its wide distribution,abundant sources and loose internal structure,high cellulose,hemicellulose and lignin content and rich in reactive groups such as hydroxyl,carboxyl and carbonyl groups.Body material,which can replace some traditional materials.Therefore,the ecological restoration waste reed is made into an adsorbent for environmental treatment,which can reduce the generation of solid waste,and achieve the dual effects of water purification and resource reuse,and improve the value of resource utilization and realize an optimized choice for energy conservation.This paper reeds on water ecological restoration is quite commonly used plant as raw materials,ammonia as activator,using Box-Behnken response surface design method,it is concluded that using ammonia activation of reed straw biomass carbon prepared by the best activation process,and its properties were characterized,and its adsorption performance of PAHs and with bitter herb joint repair effects of PAHs contaminated sediment,in order to waste recycling and fixed to find the right path of PAHs in sediment.This study mainly includes three parts:1.Optimization of activation process for preparation of reed-based biochar by ammonia method;2.Adsorption properties and structural characteristics of modified reed-based biochar;3.Analysis of fixation effect of submerged plants and biochar on PAHs in polluted sediment(1)Based on the results of the single factor experiment,the parameters were further optimized by Box-Benhnken center combination design experiment,and the BET specific surface area and iodine adsorption value were used as the response values Response surface analysis showed that all three factors affected the specific surface area of biochar,and the significant effects were:pyrolysis temperature>ammonia mass fraction>impregnation ratio.The optimum process parameters for the preparation of reed-based biochar by ammonia activation method are:pyrolysis temperature 620?,ammonia water mass fraction 8%and impregnation ratio 1:5.The specific surface area and iodine adsorption values of biochar prepared under the process conditions are respectively 334.49 m2/g and 585.52 mg/g are basically consistent with the theoretical prediction model values(335.2 m2/g,582.288 mg/g),indicating that the response surface model fits well with the actual situation,and the effective feasibility of the model is verified.(2)Diction of biomass carbon preparation by scanning electron microscopy(sem),Fourier transform infrared,CNHS characterizing the element analysis,thermogravimetric analysis,get the modified reed biochar surfaces contain rich functional groups and hydrophobic,after ammonia modification of biomass carbon channel become more smooth,pore is more apparent,porosity increase,have more regular,pore structure and surface pores,with a more developed pore structure fiber microcrystalline degrees higher.Unmodified W-620? biological carbon surface rough,a long strip,surface appear a large number of tunnels,large aperture,hole quantity is relatively small.The specific surface area of unmodified reed-based biochar was only 40.21m2/g,and the proportion of micropores was smaller,27.41%,indicating that the surface of unmodified biochar was mainly mesopores and macropores.The total specific surface area of the modified biomass carbon activated by ammonia is 357.68m2/g,which is about 8.9 times of that of the unmodified biomass carbon,with an average pore diameter of 1.871nm,and the ratio of micropore specific surface area and micropore volume of the modified biomass carbon reaches 70.88%and 69.06%,respectively.(3)ammonia activation reed of the test results show that the adsorption of biochar adsorbent additive amount of biological carbon adsorption of PAHs affect the significant effect of adsorption,adsorption process when the total content of 200 ug/L PAHs solution,the adsorption equilibrium in the solution after the PAHs removal rate with the increase of the dosing quantity rise,when m=0.1 g,total PAHs removal rate reaches 57.97%,then the increased amount of additive on PAHs removal effect is not significant,therefore in the late test selection dosing quantity is 0.1 g.The experimental results of PAHs adsorption on reed-based biochar by the initial pH value of the solution showed that the unit adsorption decreased with the increase of pH value.When the pH value was 6-8,the effect on PAHs adsorption was small.Therefore,the influence of pH value on PAHs adsorption on modified reed-based biochar was not considered in the subsequent experiments.By batch isothermal test results show that the modified reed base biochar ammonia adsorption isotherm of PAHs in water more in line with the Langmuir isotherm,belongs to the monolayer adsorption,and the modified reed base biochar of PAHs in water adsorption process conforms to the secondary adsorption dynamics model,indicating that the adsorption process mainly dominated by chemical control.(4)Four experimental groups were designed in the contaminated sediment treatment experiment:A,blank control group that only polluted sediment;B.polluted sediment+biochar group;C.polluted sediment+Vallisneria natans group;D.polluted sediment+biochar+Vallisneria natans group;The adsorption characteristics of PAHs in sediments are characterized by preferential adsorption of high-ring PAHs,especially for BeP,followed by BjFA and BjFA.The adsorption effects of BaA,Pyr and the like are also good.The experimental results show that Vallisneria natans has a good enrichment effect on the PAHs in the sediment,and the high-purity PAHs enriched in the plants are larger than the low-ring PAHs.Compared with the control group,the content of 2-3 ring PAHs in the charcoal group was significantly lower than that in the control group,and the biochar+Vallisneria natans group was lower than the other experimental groups.The experimental group added with biochar was more than the blank control group and Vallisneria natans group.The small amount of aromatics is small,indicating that biochar has a good controlled release effect on the release of polycyclic aromatic hydrocarbons in the sediment.In general,Vallisneria natans has good enrichment and treatment effects on the PAHs in the sediment.The addition of biochar can better adsorb the PAHs and inhibit the absorption and enrichment of the low-ring PAHs in the sediment.Function,can effectively block the absorption and enrichment of plants.