Study On The Nitrogen Removal Performances Of Heterotrophic Nitrifying-Aerobic Denitrifying Bacteria

In this study,a simultaneous heterotrophic nitrifying–aerobic denitrifying bacterium was newly isolated from environmental wastewater by high-throughput screening method.We identified the morphological characteristics,physiological-biochemical characteristics and biological species of this bacterium,and further characterized the metabolism characteristics and nitrogen removal performances of the strain.The performance of this strain as an inoculum for removing nitrogen from polluted rivers was examined.Results indicated that this strain was identified by 16S rRNA gene sequencing,and and compared with homology searches in GenBank using BLAST,which indicated that the strain was most closely to Klebsiella sp.in the evolutionary relationship,designated Klebsiella sp.KSND-3.Gene-specific PCR indicated the absence of the key pathway genes for nitrification and denitrification,encoding hydroxylamine oxidoreductase?hao?and nitrite reductase?nirS?,respectively,suggesting that KSND-3achieves effective nitrogen removal by another pathway.This strain possessed excellent capabilities to efficiently remove ammonium,nitrite and nitrate nitrogen sources without nitrite accumulation.With the initial nitrogen concentration of 160.00 mg·L^-1 ammonium,105.00 mg·L^-1 nitrate,8.39 mg·L^-1 nitrite and103.00 mg·L^-1 hydroxylamine removal efficiencies were 86.56%,82.03%,100%and 73.01%,respectively.When 50.00 mg·L^-1 NH₄NO₃ as a nitrogen source,the removal rates of NH₄⁺-N and NO₃^--N were 92.36%and 90.40%after 24 h,the corresponding maximum removal rates reached as high as 1.92 mg NH₄⁺-N·L^-1·h^-1 and 1.88 mg NO₃^--N·L^-1·h^-1,respectively.KSND-3 showed optimal activity at C/N ratio 8,optimal temperature of 15°C³5°C,optimal pH 5.0⁸.0 and substrate concentration less than 100 mg·L^-1.Especially,the bacterium retained over 50%of its maximal removal rate at 10°C or at a carbon to nitrogen?C/N?ratio of 4:1.This indicates that strain KSND-3 is favorable for the potential applications of wastewater treatment in wintertime or low C/N wastewater.KSND-3 was used to treat river wastewater by culturing it in a floating bed bioreactor.Ammonia nitrogen decreased significantly from 8.76 mg·L^-1initially to 1.87 mg·L^-1 in 91 days,with no NO₃^--N or NO₂^--N toxicants,indicating the great potential utility of KSND-3 in future full-scale applications in the treatment of low-C/N wastewater.Overall,these excellent performances make KSND-3 could be a promising candidate and tremendous application perspective for nitrogen removal from domestic wastewater.