Research On The Influences Of Heavy Metal Impact On The Denitrifying Property Of Heterotrophic Nitrification-Aerobic Denitrification Bacterial

The excess nitrogen emission was one of the main causes of water pollution, and eutrophication problem was still outstanding. Heterotrophic nitrification-aerobic denitrification was a new nitrogen removal technique which could achieve nitrification and denitrification simultaneously. With the rapid development of modern industry, heavy metals were inevitably discharged into domestic sewage and industrial wastewater treatment systems. Biological sewage treatment was the most widely used way at present. Excessive heavy metals had toxic effects on microorganisms and reduced wastewater treating efficiency. The individual impact of copper and zinc with different concentrations and mixed impact of iso-concentration of copper and zinc on the growth and denitrifying property of heterotrophic nitrification-aerobic denitrifying bacteria were studied. The major results were listed as follows:(1) The growing status of hterotrophic nitrification-aerobic denitrifying bacteria was different with different nitrogen sources. Among all sources, bacterial with ammonia as sources grew the best followed by mixing nitrogen, and the last one was nitrate. Both single heavy metals and mixed metal impact caused the most serious inhibition to heterotrophic nitrification-aerobic denitrifying bacteria growing and denitrifying property with nitrate as nitrogen source.(2) The existence of heavy metal ions inhibited the growth, denitrifying propertiy and degrading ability of heterotrophic nitrification-aerobic denitrifying bacterial. The results gave an order of toxicity of heavy metals on heterotrophic nitrification-aerobic denitrifying bacterial:mixed metal ions> Cu2+>Zn2+It is indicated that the coexistence of Cu2+and Zn2+could bring a synergistic inhibition on heterotrophic nitrification-aerobic denitrifying bacterial. The degree of synergistic inhibition caused by mixed metal ions was unrelated with ion concentrations while lmg/L mixed metal ions caused most toxic effects.(3) The toxic effects of Cu2+and Zn2+on the growth and denitrifying property of heterotrophic nitrification-aerobic denitrifying bacterial increased with the rise of ion concentrations. However, the inhibitions on organic degradation caused by Zn2+are unrelated with ion concentration.1mg/L and8mg/L Zn2+could promote organisms’degradation by bacterial in the experiment of impact of Zn2+on heterotrophic nitrification-aerobic denitrifying bacterial.(4). Increasing the biomass could enhance tolerance ability of the heterotrophic nitrification-aerobic denitrifying bacteria. With the increase of biomass, bacterial could resist higher concentration of heavy metals. Under the shock of1.5and2mg/L Cu2+and1,1.5,2mg/L mixed metal ions, the bacterial stopped growing and lost the ability of denitrification and degradation. At this point, the toxic effect could not be relieved when increased the biomass.