Study On The Compound Effect Of Nano Silver And Hexavalent Chromium On Biological Wastewater Treatment

Nanosilver has been widely used in textiles,medicine and household due to its excellent bactericidal properties.Because of the influence of human activities,nanosilver is inevitably released from the nanosilver-contained commodities and enters into the municipal sewage treatment plant along with the urban sewage system.Therefore,the municipal sewage treatment plant has become an important carrier of nanosilver before entering the natural environment.Biological treatment is a routine process in urban sewage treatment plants,and the inflow of nanosilver may adversely affect the efficiency of sewage treatment.Heavy metals are typical toxic pollutants in sewage and self-produced wastewater.Chromium is the typical pullutant of these heavy metals and is present in wastewater from steel manufacturing,leather tanning and leachate.Cr(Ⅲ)or Cr(Ⅵ)is a common form of chromium in natural water bodies,although Cr(Ⅲ)is an essential micronutrient in human and animal food,the Cr(Ⅵ)is usually considered a potential carcinogen,and related to industry such as the production of stainless steel,metal plating,paint,leather processing,catalyst.Cr(Ⅵ)is oxidizing and nanosilver is reducing,both of which have a certain impact on the treatment efficiency of sewage treatment plants.Studies showed that Cr(Ⅵ)has synergistic or antagonistic inhibitory effects on microorganisms when co-existing with other heavy metals,such as Ni(Ⅱ),Cu(Ⅱ)and Fe(Ⅱ).At present,there are many studies on the effect of nanosilver on water treatment system,but few studies have discussed the interaction between nanosilver and other heavy metals in sewage and the combined effect of nanosilver and other heavy metals on water treatment system.In this paper,the combined effect of different concentrations of nanosilver(0.1,1 mg/L)and hexavalent chromium(1,5,10,20 mg/L)was studied on the sewage treatment system.The study found that the nitrogen removal function of the system was significantly inhibited with the increase of operating time and the concentration of hexavalent chromium,the inhibitory effect gets more obvious.With the increase of the operating cycle,the content of nitrate nitrogen in the effluent water of the system gradually decreases,but it has no obvious influence on the removal of COD and TOC in the whole operating cycle.However,only when the concentration of hexavalent chromium reaches 20mg/L,the phosphorus removal effect of the system is inhibited.In the whole operating cycle,the nanosilver and hexavalent chromium did not have the compound effect on the SBR system.It wasalso found that most of the nanosilver and hexavalent chromium were adsorbed by the sludge,and gradually accumulated in the sludge.SEM were used to observe the agglomeration of nano silver on the surface of sludge,and when the agglomeration was surface scanned,it was found that the distribution of silver and sulfur elements presented certain similarity,while the content of Cr elements was less.