| Nitrate pollution in the source of drinking water has caused worldwide concern due to the presence of carcinogenic and teratogenic risk. Because the dissolved nitrate can not be effectively removed during the traditional drinking water purification process which is designed to mainly remove the colloidal substances. Among several practical methods for nitrate removal, ion exchange process seems to be the most suitable technology for nitrate removal owing to its characteristics of simple, efficient, renewable and low cost. In this study, the sources, harmful effects to human and the removal methods of nitrate were summarized, and a nitrate selective macroporous anion exchange resin was synthesized for nitrate removal from drinking water. Hoever, the ion exchange resin service life was relatively short, needed to regenerate and the regeneration fluid contained a high concentration of nitrate and sulfate, which made it harder for subsequent processing. Therefore, in order to obtain economic and efficient processing method, the batch experiments were carried out to study the adsorption isotherm, adsorption kinetics, adsorption thermodynamics and adsorption isotherm model, dynamic adsorption tests using the green, safe and low-cost, to elucide the properties of self-made selective macroporous anion resin. The results of nitrate adsorption experiments and the application conditions of synthesized resin were concluded as follows:(1) The optimum amount of synthesized resin was 0.2 g at an initial nitrate concentration of 100 mg/L; solid/liquid ratio was 4.0 g/L; the influence of temperature on nitrate adsorption was insignificant; it was understandable that the existence of competing anions strongly interfered with the adsorption of nitrate, and the ordering of the influences of them were: SO42- > Cl- > HCO3-; The selectivity coefficients indicated that the synthesized resin had strong selective adsorption ability to nitrate; the adsorption capacity of synthesized resin was decreased by 5% of adsorption capacity after 5 times regeneration, and the regenenration rate was up to 94.5 % after 10 times regeneration. Consequently, the synthesized resin had excellent adsorption selectivity for nitrate and reproducibility.(2) The behavior of the nitrate adsorbed onto the synthesized resin showed a better fitting to the Langmuir isotherm model and Pseudo second-order kinetic model, and the intra-particle diffusion was the main rate-limiting step. Aadsorption rate was fast which half of nitrate could be remove in 10 min, and the adsorption equilibrium reached in 30 min. So the resins adsorption process was spontaneous endothermic reaction.(3) The results of dynamic adsorption tests showed that the breakthrough time decreased with the increase of flow velocity and NO3- concentration of inflows, and the influence of flow velocity on nitrate adsorption capacity of synthesized resin was insignificant. The optimal H/D ratio was 20; the maximum nitrate adsorption capacity of static experiments was 19.47 mg/g, which was lower than that of dynamic experiments 23.11 mg/g.(4) Coexisting ions had less influence on regeneration, NO3- regeneration rate was 80.2% to 93.4%, indicating that the synthesized resin had excellent selectivity under the existence of competing anions and priority to adsorpte nitrate. The utilization rate of adsorption column could reach to 68.6 % to 92.0 %.(5) The results of fixed bed experiments showed that the optimum regeneration solution was 8 % of NaCl solution. The efficiency of desorption could reach 98.5% by 2 h regeneration under the flow rate of 33.5 mL/min. The regeneration rate of fixed bed was negative correlated with the flow velocity of regeneration solution, and was positive correlated with time. The volume and cost of regeneration could be significantly decreased since 99.2 % of desorption efficiency was obtained with 18 BV of 8 wt. % salt solution, indicating that the anion exchange resin had excellent selectivity and reproducibility for nitrate adsorption. |
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