Preparation Of Adsorbent By Sodium Citrate Tribasic Modified Drinking Water Treatment Sludge For Ammonia Nitrogen Removal From Wastewater

Excessive ammonia nitrogen into water will cause abnormal algal reproduction,resulting in the decline of water quality and affect the environmental sanitation.Adsorption has the characteristics of low energy consumption and high efficiency,which is one of the effective methods to remove ammonia nitrogen from water.drinking water treatment sludge（DWTS）is rich in soil particles,iron and aluminum oxides and other substances.Its surface is rough and porous,and it also contains a large number of active sites of Fe,Al and Si,so it has a good adsorption effect on pollutants in water.In this experiment,drinking water treatment sludge was used as raw material,and under different baking and modification conditions,the modified particle adsorbent was prepared by grinding-modification-granulation-baking.Taking ammonia nitrogen adsorption capacity as the measurement index,the optimal modified particle adsorbent was screened and its static and dynamic adsorption performance for ammonia nitrogen in water was explored.（1）The baking experiment results of DWTS showed that the specific surface area and adsorption capacity reached the maximum at 500℃for 5h,which were 50.61m²/g and 0.695mg/g,respectively.The experimental results of modification of DWTS showed that trisodium citrate dihydrate with the concentration of 0.5mol/L had the best modification effect,and the adsorption capacity reached 1.926mg/g,which was 2.77times that of unmodified DWTS.（2）EDX characterization results show that the main elements of DWTS were O,Si,Al,C,after the modification with sodium citrate tribasic,Na⁺was introduced into the sludge through displacement.BET and SEM characterization results show that compared with the raw sludge particle adsorbents,the number of surface lamellae of the modified particle adsorbents was more and more loose,and the pore size,total pore volume and specific surface area were increased.XRD characterization results showed that the main phase composition of raw sludge and modified particle adsorbents is Si O₂and Al₂O₃.（3）The experimental results of the influencing factors of the adsorption of ammonia nitrogen by raw sludge and modified particle adsorbents show that the saturated adsorption time of the two kinds of particulate adsorbents was 4h and 6h,the optimal dosage was 60g/L and 20g/L,respectively,and the optimum pH of the solution was 7.The presence of Zn²⁺and Al³⁺in the solution has a greater effect on the adsorption of ammonia nitrogen.（4）The adsorption process of the modified particle adsorbent and raw sludge particle adsorbent on ammonia nitrogen accorded with the Langmuir isotherm adsorption model,indicating that the adsorption is single layer adsorption.According to the separation factor R_L value,the adsorption of ammonia nitrogen on the two kinds of particle adsorbents is favorable.The fitting results of kinetic models showed that the adsorption process of the raw sludge particle adsorbent and modified particle adsorbent on ammonia nitrogen accorded with the Pseudo-second order kinetics,indicating that the adsorption process was chemisorption.The initial adsorption rate H₀calculated by the pseudo-second-order kinetic model shows that the initial adsorption rate of the modified particle adsorbent is higher than that of the raw sludge particle adsorbent.（5）Regeneration and reuse experiments have shown that the optimal regeneration solvent of the saturated modified particle adsorbent was 0.1mol/L of NaOH,after five times of desorption and regeneration,the removal rate of ammonia nitrogen by modified particle adsorbent was decreased by 6.53%.（6）The dynamic adsorption experiments of modified particle adsorbent on ammonia nitrogen show that the glass column filled with modified particle adsorbent has a good adsorption effect on ammonia nitrogen.When the initial ammonia concentration and influent flow rate are increased,the breakthrough time of the adsorption column and the removal rate of ammonia nitrogen decrease.The breakthrough time and removal rate increased with the increase of column height.Therefore,higher adsorption column height,lower initial concentration of ammonia nitrogen and influent flow rate are favorable for adsorption.BDST model and Thomas model can better describe the dynamic adsorption process of ammonia nitrogen by adsorption column.BDST model can be used to predict the breakthrough time when the concentration of ammonia nitrogen is changed.Thomas model can evaluate the theoretical adsorption capacity of ammonia nitrogen by adsorption column under different initial conditions.In conclusion,the preparation of particle adsorbents by modifying DWTS has the advantages of low cost,good adsorption performance and recycling,which has a good application prospect in the treatment of ammonia nitrogen wastewater.