Effect Of Heavy Metals On Biodenitrification And Simultaneous Removal Of Nitrate And Heavy Metals Using Immobilization Technology

Excessive nitrate in water,which not only causes water eutrophication,but also seriously impacts on human health,has become a global concern.Biological denitrification has demonstrated environmentally friendly method for removing nitrate,however,it shows only low nitrogen removal efficiency when heavy metals and organic matters are co-existing in the complex wastewater,it therefore limits the denitrification efficiencicy.This study explores the effect of different concentrations of Cu(?)and Zn(?)on the denitrification of Paracoccus sp.YF1,as well as simultaneously removal of nitrate and heavy metals using immobilization of Paracoccus sp.YF1 onto carriers.The main results are summaried in this study as following.The effects of different concentrations of Cu(?)or Zn(?)on microbial growth,total protein secretion,nitrogen removal efficiency and nitrite accumulation during denitrification were compared.The reults showed that a low concentration of Cu(?)(0.01 mM)severely inhibited the growth of microorganisms,the secretion of proteins,and the efficiency of denitrification,while the inhibition became more severe when the concentration of Cu(?)increased;in contrast,the concentrations of heavy Zn(?)were less than 0.2 mM and promoted microbial growth,protein secretion,and efficiency of denitrification,however,a high concentrations of Zn(?)(more than 0.2 mM)exhibited inhibition.In addition,the effect of Cu(?)or Zn(?)on the accumulation of nitrite showed that the accumulation time and the amount of accumulation of nitrite were increased along with a higher the concentration of Cu(?)or Zn(?).The reults obtained from SEM-EDS,FTI and XPS showed that Cu(?)or Zn(?)influenced the morphology and surface functional groups of the microorganisms in degradation.To improve the resistance of microorganisms and obatin simultaneous removal of nitrate and heavy metal,the immobilized Paracoccus sp.YF1 onto carriers was proposed.Compared to the removal of nitrate and heavy metals using bagasse,bamboo charcoal and zeolite.The results showed that bamboo charcoal was best,and further roasting modified bamboo charcoal for nitrate and heavy metal of Cu(?),removal rates were up to 23.2%,98%,but immobilized Paracoccus sp.YF1 on bamboo charcoal significantly improved the removal of mixed nitrate and Cu(?)than free stains.After 48 h biodegradation using the initial concentration of 5 mM nitrate and 0.1 mM Cu(?),the removal rate of nitrate and Cu(?)were 97.7%and 98.0%,respectively.To understand the stability and reuse of the immobilized cells,removal rate of nitrate and Cu(?)by the immobilized cells were 80%and 70%,respectively after 5 recycles.The mechanism of nitrate removal is proposed based on the synergistic effect of bamboo charcoal adsorption and biodegradation,while the removal of copper mainly depends on the adsorption of bamboo charcoal.