| Due to the accelerated construction of industrialization and the excessive use of nitrogen fertilizer,more and more surface water and groundwater resources have been polluted by nitrate.The pollution of nitrate leads to the ecological and economic value reduction of rivers and lakes and poses a threat to human health.Therefore,it is of great practical significance to explore the economic and efficient treatment technology for nitrate contaminated water.At present,Fe/C micro-electrolysis technology has attracted more and more attention in the field of nitrate removal in water due to its low processing cost and no need for additional chemicals.In micro-electrolysis reaction,nitrate is reduced by obtaining active electrons transferred from the surface of activated carbon.But generally,nitrate need to adsorb on the surface of activated carbon before it get the electrons to be reduced.However,the adsorption capacity of ordinary activated carbon to nitrate is poor,which limits the nitrate removal effect of micro electrolysis.In this study,waste iron scraps and ordinary activated carbon were used as raw materials to form micro-electrolysis system.The effect of Fe/C micro-electrolysis on the removal of dissolved nitrate in water was studied,the effects of Fe/C dosing,Fe/C dosing ratio,and initial pH on the removal efficiency of micro-electrolysis were discussed.Then the surfacemodificationofactivatedcarbonwascarriedoutthrough cetyltrimethylammonium chloride?CTAC?to increase the adsorption amount of nitrate anion on the surface of activated carbon,which promotes the nitrate reduction reaction on the surface of activated carbon.Through the contrast experiment,it was found that the reduction rate of nitrate concentration during the early stage of micro-electrolysis reaction was accelerated by the surface modification of activated carbon and the reduction reaction of nitrate on the surface of carbon was promoted.The main results of the study are as follows:?1?The removal rate of nitrate in water by the micro-electrolytic system composed of scrap iron and common activated carbon is greater than the sum of separate removal rate by scrap iron and common activated carbon,which proves that the micro-electrolytic reaction system has been successfully constructed.The nitrate decreased from 20 mg·L-1 to 8.44 mg·L-1 when Fe/C=3:1,total dosage of Fe and C is10 g·L-1,DO<1 mg·L-1,initial pH is neutral,T=25°C and reaction time t=210 min.?2?Through the comprehensive analysis of material characterization,the successful load of CTAC on activated carbon surface was proved.After modified by CTAC,the specific suiface of activated carbon was significantly reduced,but the pore volume did not show a continuous decline.It was founded that the surface of activated carbon changed from smooth to rugged by SEM images.Also,the stretching vibrations of C-H and deformation vibrations of-CH3-and-CH2-,which belong to CTAT long alkyl chain,were found on the surface of activated carbon by Fourier infrared spectroscopy.The thermogravimetry analysis showed that after modified by CTAC,the weight loss rate of activated carbon in the range of 152.79-655.82°C increased.?3?Surface modification of activated carbon by surfactant CTAC can improve its adsorption capacity for nitrate in water.After modified through 10mmol·L-1?25mmol·L-1?50 mmol·L-1?100 mmol·L-1 CTAC,the maximum adsorbing values of acivated carbon increase from 1.226 mg·g-1to 1.542 mg·g-1,1.89 mg·g-1,2.578 mg·g-1and 2.824 mg·g-1,respectively.The adsorption behavior of modified activated carbon to nitrate in water conformed to a pseudo-first-order adsorption kinetic model.?4?The micro-electrolytic system composed of modified activated carbon and iron scrap showed a higher removal rate for nitrate than ordinary activated carbon and iron scrap.the increase of nitrate removal rate is greater than the increase of nitrate adsorption by modified activated carbon,which proved that the conductivity of CTAC has a promoting effect on the electrode reaction.The nitrate removal rate of micro-electrolytic composed of modified activated carbon and ion scrap was 83.4%when Fe/C dosage ratio is 3:1,DO<1mg·L-1 and the pH is neutral.The micro-electrolytic system composed of modified activated carbon and iron scrap is less affected by the concentration of dissolved oxygen in water,but coexistence of anions,such as Cl-,SO42-,CO32-and HCO3-,and humic acid has a significant influence on the removal rate. |
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