Preparation Of Sewage Sludge-based Activated Carbon By Nitrogen-functionalizaton And Its Application In Perchlorate Removal

Perchlorate could enter into human through water and food，it had similar charge andionic radius to iodine ion, it will inhibit the combination of thyroid and iodine ion and weakenthe secretion of thyroid hormone, so it could hinder the growth of human. Furthermore,perchlorate could act on the fetus through maternal and brought greater harm to the fetus’sdevelopment. Therefore, it is imminent to strengthen the prevention and management ofperchlorate and it has vital significance to develop an efficient removal method ofperchlorate.As a good porous material, activated carbon was widely used in various aspects ofpollutant treatment but it was confirmed to have limited adsorption capacity to perchlorate. Itcould obtain better perchlorate removal capacity through modification. Sewage sludge-basedactivated carbon (SAC) made from excess sludge that produced in water treatment plant hadvery low cost and it demonstrated similar surface structure. The development of perchlorateadsorbent with SAC brought great economic and environmental benefits as it could realizesludge dispose and perchlorate removal simultaneously. In this paper, original SAC wasobtained by pyrolysis of excess sludge under ammonia atmosphere and then modified withnitrogen-functionalization to enhance the adsorption capacity of perchlorate. The treatment ofnitrogen-functionalization including three steps: oxidation activation、ammonization andmethylation. Oxidation activation by nitric acid or hydrogen peroxide could increase thesurface area and pore volume apparently and it increased the oxygen content of SAC.Ammonization treatment could bring further improvement of the surface aperture structureespecially the micropore. More important, ammonization could increase the content ofpyridine (N-6) and quaternary ammonium (N-Q) which played the key role in the perchlorateremoval of SAC by specific combination. Methylation treatment of SAC transferred pyridineinto alkyl pyridine. It leaded to slight reduction of surface area and pore volume but improvedthe content of N-Q. The original SAC was obtained from sludge pyrolysis and the surfacearea and pore volume was22.14m2/g,0.039cm3/g respectively. It contained low content ofN-6and no N-Q and the breakthrough volume was only600BV in the perchlorate removalwith the concentration was80ppb. The adsorption capacity was greatly enhanced through thetreatment of nitrogen-functionalization. The adsorption capacity to perchlorate of SACactivated by nitric acid or hydrogen peroxide during nitrogen-functionalization was increased to6.5times and5.8times respectively compared to original SAC. As a whole, it was better tochoose nitric acid as the activation than hydrogen peroxide.Both the change of ammonization temperature and time leaded to the variation ofsurface characteristics and affected the adsorption capacity to perchlorate of SAC. When theammonization temperature was fixed as750℃, prolonging ammonization time enhance theadsorption capacity of perchlorate because it brought higher surface area and pore volume andincreased the content of N-6and N-Q in SAC. When ammonization time was chosen as90min, the rising of temperature was helpful to obtained higher content N-Q, but the surfacearea and pore volume got decreased when the temperature surpassed750℃because too hightemperature will damage the surface pore structure of SAC. To the perchlorate removal,adsorption capacity of SAC activated by nitric acid during nitrogen-functionalization wasincreased with the rising of ammonization temperature and the highest adsorption capacity ofSAC activated by hydrogen peroxide was obtained as ammonization temperature was750℃.Through the experiments we find that perchlorate removed bynitrogen-functionalization SAC was the corporate function of physical adsorption andchemical adsorption and chemical adsorption played the leading role. The optimum range ofpH was6.3～8.1and the adsorption capacity got great decrease under strong alkalineconditions. When the solution pH was7.4and perchlorate concentration was80ppb, SACobtained through nitrogen-functionalization with the ammonization temperature was750℃and ammonization time was120min exhibited the best perchlorate removal ability. Thebreakthrough volume of SAC activated by nitric acid or hydrogen peroxide duringnitrogen-functionalization was4400BV,4200BV respectively. The adsorption capacity ofSAC regenerated by microwave was still keep good level when it used for10times.