Removal Of Nitrate From Industrial Wastewater By Use Of Denitrifying Bacteria

In this study,two novel denitrifying bacteria were successfully isolated from industrial wastewater and soil samples.Using morphological,biochemical/biophysical and 16S rRNA gene analyses,these two bacteria were identified as Stenotrophomonas sp.ZZ15 and Oceanimonas sp.YC13,respectively.Both of these two bacteria showed efficient NO₃^--N removing abilities under a semi-anaerobic condition without obvious accumulation of NO₂^--N,NH₄⁺-N and N₂O-N.The DO and pH values in the whole course of the denitrification process in the nitrate broth were also tested,and the results showed that nitrate removal rates moved to a high degree after the DO values maintained at lower values of less than 1 mg/L and the change of pH showed that ZZ15 possibly excreted some acidic compound.NO₃^--N removal from paper mill wastewater was also successful by treatments with either a denitrifier or denitrifiers mixture without accumulation of NO₂^--N,NH₄⁺-N and N₂O-N.But the NO₃^--N removing efficiency of mixed denitrifiers was almost the same as single denitrifier.In order to recycle the microbial cells,the cells of each denitrifier were immobilized in a hybrid matrix of particles made by calcium alginate(CA) and polyvinyl alcohol(PVA).The optimum condition of immobilization is PVA concentration 8%, sodium alginate(SA) concentration 2%,CaCl₂ concentration 6%and with sustaining time 18 h.The outside and inside structure of immobilized particles were observed by scanning electron microscopy(SEM),and the morphologies of original and immobilized strains were also compared.Strain ZZ15 seemed to excrete some extracellular polymeric substances(EPS) into the immobilized particles,but YC13 not.Bacterial immobilization experiments were also performed in the same wastewater.It took 3 days to reach the national discharge standard of NO₃^--N without the accumulation of NO₂^--N and NH₄⁺-N.Therefore,this study provides valuable denitrifying bacteria in biotreatment of industrial wastewater and other environmental pollution caused by NO₃^-/NO₂^-.