| At present,the problem of water pollution is increasingly serious.Water pollution can be divided into industrial wastewater and domestic wastewater according to their sources.Dye wastewater is one of the main harmful industrial wastewater.If it is discharged directly into the environment without effective treatment,it will affect the ecosystem.Water eutrophication is a phenomenon of water pollution caused by excessive nitrogen,phosphorus and other nutrients.These nutrients mainly come from the unreasonable discharge of agricultural fertilizer,domestic wastewater and industrial wastewater,which will affect the living environment of aquatic organisms.As one of the common treatment methods to remove water pollutants,adsorption method has the advantages of easy operation,simple equipment,green and so on.Because water purification sludge has developed pore structure,large specific surface area and other characteristics,it can be used as a potential adsorption material.In addition,hydrothermal treatment is a simple,efficient and cost-saving technology.Hydrothermal carbon has higher polarity and a higher proportion of oxygen-containing functional groups,but also retains more active adsorption sites.The adsorption capacity and selectivity of hydrothermal carbon to pollutants can be improved by modifying the material.However,there are few researches on the hydrothermal modification of water purification sludge.Therefore,this paper prepared the corresponding adsorbent by hydrothermal modification of water purification sludge and carried out adsorption studies on methylene blue(MB),ammonia nitrogen and phosphate pollutants respectively.The optimum preparation conditions of the modified material were determined and the effects of various single factors on its adsorption of corresponding pollutants were investigated.The structure and physicochemical properties of water purified sludge before and after modification were analyzed by SEM,FTIR and other characterization methods.The adsorption characteristics were analyzed by adsorption isothermal model,adsorption kinetics model and adsorption thermodynamics.The adsorbent(WTSA)was prepared by modifying water purification sludge by hydrothermal treatment.The results of the adsorption on MB showed that WTSA7(hydrothermal temperature 260℃,hydrothermal time 9h)was the best preparation condition.Under certain conditions,the adsorption capacity and removal rate of WTSA7 for 50 mg/L MB were 29.73 mg/g and 89.18%,respectively.The characterization results showed that WTSA7 had rough surface,loose structure and developed pore structure.The pore volume and average pore diameter of the modified material increased,while the specific surface area of the modified material decreased compared with the original mud.The materials before and after modification have abundant functional groups,which can adsorb cationic dye MB by electrostatic attraction,hydrogen bond and π-π interaction.In the presence of K+,Na+,NO3-and Cl-,the adsorption capacity of WTSA7 to MB decreased.The effect of K+on the adsorption of MB by hydrothermal carbon was greater than that of Na+,and the effect of Cl-on the adsorption of MB by hydrothermal carbon was greater than that of NO3-.Among the fitted adsorption models,Freundlich isothermal adsorption model and quasi-second-order kinetic model were more consistent with the data of WTSA7 adsorption MB,respectively,indicating that the adsorption process was mainly chemisorption of multiple molecular layers.Thermodynamic results showed that the adsorption of MB by WTSA7 was a spontaneous endothermic and entropy increasing process.The adsorbent(WTSB)was prepared by modifying water purification sludge by alkaline hydrothermal treatment.The results of the adsorption on ammonia nitrogen showed that the modified material could effectively improve the adsorption of ammonia nitrogen.WTSB5(hydrothermal temperature at 210℃,mass concentration of NaOH at 5%,hydrothermal time at 6h)had a better adsorption effect on ammonia nitrogen,and the adsorption capacity was 1.46 mg/g,which was about 5.03 times that of original mud(WTS).The adsorption capacity of WTSB5 to ammonia nitrogen was enhanced by cation exchange and electrostatic attraction of hydroxyl group on the surface of the material.The characterization results showed that the WTSB5 structure became rough and loose,and the specific surface area decreased.The Na+with small radius was replaced with some cations in the water purification sludge pores,which increased pore volume,decreased Si/Al ratio and enhanced cation exchange characteristics.The adsorption process of ammonia nitrogen by WTSB5 was well fitted with Freundlich isothermal adsorption model and quasi-second-order kinetic model,and the intra-particle diffusion model showed that the adsorption process of MB by WTSB5 was controlled by membrane diffusion and intra-particle diffusion.The thermodynamic results showed that the adsorption of ammonia nitrogen by WTSB5 was a spontaneous endothermic process,and the adsorption was an entropy-increasing process,which increased the disorder degree of material at the solid-liquid interface.Preparation of adsorbent(WTSC)by loading lanthanum alkali hydrothermal modification treatment of water purification sludge,and the research results of phosphorus showed that:WTSC1(loading lanthanum alkaline hydrothermal temperature 170℃,hydrothermal time 3h)was the best preparation conditions.Under certain conditions,the adsorption capacity of WTSC1 to 50 mg/L phosphorus was 24.57 mg/g,and the removal rate reached 98.29%.The characterization results showed that after modification,the surface of water purification sludge was loaded with a certain amount of lanthanum,and the surface was granular and rough,which increased the BET specific surface area of the material,improved pore volume and aperture,increased the active adsorption sites,and enhanced the adsorption capacity of phosphorus.The adsorption processes of phosphorus by WTSC1 were mainly electrostatic attraction,ligand exchange and surface precipitation.In the coexistence system,the presence of Cl-,NO3-and SO42-in the solution had relatively no effect on the adsorption process of phosphorus by WTSC1.However,the high concentration of HCO3-had a certain effect on the adsorption process of WTSC1,because it increased the pH of solution and competed with PO43-for the active adsorption site,which was not conducive to the adsorption process.The adsorption process of WTSC1 was consistent with Freundlich isothermal adsorption model and quasisecond-order kinetic model,indicating that the adsorption process was mainly multi-molecular layer chemisorption.In addition,thermodynamic results showed that the adsorption of phosphorus by WTSC1 was endothermic and spontaneous with increasing entropy.In conclusion,adsorption of MB by WTSA1,ammonia nitrogen by WTSB5 and phosphate by WTSC1 all have certain removal effects.It not only provides a reference for solving the water pollution problem,but also realizes the resource utilization of water purification sludge,and reduces the environmental pollution and resource waste caused by the traditional treatment of sludge,which has a certain significance. |
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