Study On The Adsorption And Removal Technology Of Nitrate In Groundwater By Ion Exchange Resin

With the rapid development of industry and agriculture and the lack of environmental protection measures,groundwater pollution is becoming more and more serious,among which nitrate pollution is the most prominent.Ensuring the safety of groundwater is important to the battle against pollution.And it is the only way to improve the quality of life of residents.Strengthening the prevention and control of groundwater pollution and developing new remediation technologies to save the contaminated groundwater are urgent at present.Permeable Reactive Barrier technology is a mature groundwater repair technology which has the advantages of high treatment efficiency,low operating cost,easy operation and less environmental interference,etc.It is also a hot topic in the field of groundwater remediation.As a water treatment adsorbent,resin has the characteristics of large adsorption capacity,corrosion resistance,long activity,good reproducibility,strong adsorption selectivity,non-toxic and harmless to the environment,etc.Ion exchange resin plays an important role in water treatment and it also has a wide prospect in the field of groundwater remediation.In the experiment,NDM-2 resin was used as the adsorption material,and groundwater polluted by nitrate was used as the treatment object,and a series of single factor experiments were carried out.Through static adsorption experiments,study the behavior of adsorbents on nitrate,and explore the adsorption stability of adsorbents under the change of environmental factors;Resin was used as active medium in the treatment of nitrate contaminated groundwater using PRB column to simulate Permeable Reactive Barrier.Based on the experiment,the feasibility and effectiveness of PRB technology using resin as active medium to treat groundwater polluted by nitrate were demonstrated;The adsorbent was regenerated by chemical regeneration and biological regeneration,and the adsorption performance of the adsorbent after regeneration was studied.（1）With the initial nitrate concentration of 100 mg/L and the resin dosage was 0.05 g,the adsorption equilibrium was reached in 4 h,and the equilibrium adsorption capacity was125.01 mg/g;The adsorption process conformed to the quasi-first-order kinetic model and the adsorption rate was mainly controlled by electrostatic action;The influence of different temperature on adsorption was studied,as the temperature rose,the adsorption capacity of NDM resin for nitrate decreased;At 298 K,both Langmuir and Freundlich models can well reflect the adsorption behavior of resin;The adsorption capacity of the adsorbent was affected by the pH value of the solution.With the pH value of 6,the adsorption capacity of the adsorbent was the best;The salinity in the solution would interfere with the adsorption of nitrate by the adsorbent,and as the salinity increased,the nitrate adsorption capacity of the resin decreased significantly;Coexisting anions would interfere with the selective adsorption of nitrate in the order of SO₄^2->Cl^-.（2）In the simulated column experiment,with the influent flow rate of 2.44 m L/min,the penetration volume of 16.09 L,and the resin adsorption capacity of 153.99 mg/g,which was greater than that of the static adsorption experiment;The inlet flow rate should not be too high,when the flow rate was too high,the slope of the penetration curve was large,the penetration point moved forward,and the phenomenon of channeling was easy to occur,and the adsorption performance of the resin cannot be better played;The Cl^-and SO₄^2-in the system can occupy the adsorption site through competition,reducing the adsorption capacity of the resin for nitrate,and the order of interference was Cl^->SO₄^2-.（3）In the chemical regeneration,NaCl had good regeneration performance for adsorbing saturated resin.With the NaCl concentration of 1.2 mol/L,the desorption efficiency of nitrate in the resin was the highest,reaching 90.91%.After 14 repeated adsorptions-regenerations,the adsorption capacity of the resin decreased slightly,but it still remained above 87%of the original resin;Using 1.2 mol/L NaCl as the regenerant to desorb the nitrate in the saturated resin,adjust the water flow rate to 3.46 m L/min,with the BV of 47.36,the saturated resin can be completely regenerated.（4）In the bioenhanced regeneration,when the regeneration system did not add NaCl,the resin regeneration was not complete.After 12 h regeneration,there was still a small amount of nitrate in the resin cannot be removed,and the resin adsorption capacity decreased significantly;When NaCl was added into the system,the resin could be completely regenerated within 7 h.After five times of repeated adsorption-regeneration-adsorption in this system,the loss of resin adsorption capacity was small.The maximum loss was only 5.5%,and the adsorption capacity fluctuated in the range of 146.56～151.98 mg/g.