| Excessive nitrogen and phosphorus in water will lead to eutrophication,which leads to water pollution,ecological environment destruction and even threats to human life.However,nitrogen and phosphorus are necessary nutrients for plant growth,so it is urgent to find a way to transfer nitrogen and phosphorus from water to solid phase.In this paper,powder biomass carbon,rapidly prepared by in-situ pyrolysis of waste biomass,was used as an adsorbent for fluidized adsorption of eutrophic elements(nitrogen and phosphorus)in water,realized the effective enrichment of nitrogen and phosphorus from liquid to solid phase.Finallly,the biomass carbon riched in carbon,nitrogen and phosphorus was used as fertilizer to return to the soil,which maximally promoted the macro recycling of carbon,nitrogen and phosphorus,improved the recycling efficiency,and reduced the energy consumption of waste biomass treatment and environmental pollution.In this study,the static adsorption properties of powder biomass carbon to nitrogen and phosphorus in water were investigated.The desorption performance of biomass carbon(NxPy@C)in simulated soil water environment after adsorption of nitrogen and phosphorus was studied,which investigates the feasibility of NxPy@C as a sustained-release fertilizer.In order to further enhance the enrichment of nitrogen and phosphorus by biomass carbon,a simple fluidization device was designed,and the solid-liquid two-phase flow of carbon-water in the self-made fluidization device was preliminarily simulated and analyzed by CFD.1.The static adsorption performance of nitrogen and phosphorus in water by powder biomass charcoal was studied.The experimental results showed that the coconut shell biomass carbon(CAC)and woody biomass carbon(WAC)had good adsorption performance for phosphate and nitrate in water,and reached equilibrium after adsorption for 60 min.Within the experimental range,when optimum pH value for the adsorption was 6-7(pH is slightly acidic),the extent of adsorption of phosphate(nitrate)by biomass carbon in water increased significantly with increasing initial concentration,decreasing added biomass carbon,decreasing paticle size of biomass carbon and increasing temperature.The adsorption effect is also affected by the presence of other ions in the solution,for example,NH4+ promoted the adsorption of phosphate or nitrate by biomass carbon,while,N03-(P043"),SO42-and CO32-inhibited the adsorption of phosphate or nitrate by biomass carbon.In order to further understand the adsorption process,the kinetic and isothermal models were establishied,showed that the adsorption process of phosphate by CAC and WAC is more suitable to be described by Freundlich model and pseudo-second order model,while the adsorption process of nitrate by CAC and WAC is more suitable to be described by Langmuir model and pseudo-second order model.According to the Langmuir model,the maximum adsorption capacity of CAC and WAC for phosphate at 30? is 1.38 mg/g and 1.37 mg/g respectively,and the maximum adsorption capacity of CAC and WAC for nitrate at 30? is 0.40 mg/g and 0.31 mg/g respectively.According to thermodynamic analysis,the adsorption process of phosphate and nitrate in water by biomass carbon is an endothermic process with entropy increase,which is spontaneous and combined by various mechanisms,such as liquid film diffusion and surface adsorption.CAC and WAC adsorb phosphate and nitrate in water by means of van der Waals force,electrostatic force,hydrogen bond formation and ion exchange.2.In this paper,the desorption process of NxPy@C in simulated soil-water environment was studied.The results showed that the desorption of nitrate by CAC and WAC was basically balanced after 60 min and the desorption of phosphate was basically balanced at 90 min.Within the experimental range,the desorption effect of biomass carbon on nitrogen and phosphorus was increased with the increasing desorption temperature,the increasing value of pH and decreasing solid-liquid ratio.In addition,the actual desorption conditions also need to consider the plant growth and other factors.In order to realize process of desorption,the desorption kinetics and isotherm models were established,showed that the desorption process of phosphate by CAC and WAC is more suitable to be described by Freundlich model and pseudo-second order model,while the desorption process of nitrate by CAC and WAC is more suitable to be described by Langmuir model and pseudo-second order model.Through Langmuir model,it can be calculate that the maximum residues of CAC and WAC for phosphate at 30? were 1.004 mg/g and 0.886 mg/g,respectively,and the maximum residues of CAC and WAC for nitrate were 0.351 mg/g and 0.240 mg/g,respectively.Phosphate and nitrate on the surface of biomass carbon were desorbed into the simulated soil-water environment by means of hydrogen bond breaking,ion exchange and diffusion.3.In this paper,powder biomass carbon and water was used as the solid phase and liquid phase,respectively.The critical fluidization velocity is 0.261cm/s,and the strip velocity is 22.584cm/s,which were calculated through experiments and relevant formulas.So the dimensions of the fluidization unit are determined.The diameter and height are 0.2 m and 1.0 m,respectively.The exit is tapered with a diameter of 0.1 m and a height of 0.15 m.The flow process of solid-liquid phase in a fluidized device was simulated by CFD.The k-?turbulence model,the Euler-Euler dual fluid model and and the Gidaspow model were used for liquid phase flow,water-powder biomass carbon two-phase flow and the drag force between liquid and solid,respectively,to explore the solid holdup and particle velocity distribution.The simulation results show that the solid holdup and biomass carbon velocity in the fluidized plant are distributed symmetrically along the central bearing,and are not uniformly distributed along the X-axis and Y-axis under the influence of the circulating flow region.The uneven distribution of velocity of biomass carbon powder results in the circulation flow near the wall and the non-uniformity of solid holdup increases.In a word,biomass carbon has a good adsorption and desorption capacity for phosphate and nitrate in water.The fluidization device is used to further improve its adsorption performance,so that the NxPy@C can be used as fertilizer to return to the soil and better complete the carbon cycle.This study provides a new idea for the disposal of waste biomass and the improvement of carbon recycling efficiency,and provides theoretical support for further research. |
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