Isolation,Identification And Denitrification Characteristics Of Heterotrophic Nitrification-aerobic Denitrification Bacteria From Rubber Processing Wastewater

Natural rubber is an important industrial raw material and strategic resource,but the natural rubber processing will produce a large number of high concentration ammonia nitrogen organic wastewater,which will cause serious pollution to the environment.At present,the economic,green and easy biological nitrogen removal technology is mainly used for the treatment of nitrogen in natural rubber wastewater.With the discovery and utilization of heterotrophic nitrification-aerobic denitrification bacteria,it is of great practical significance to isolate and screen HNADs,which has good nitrogen removal rate and can adapt to special environment.In this study,a heterotrophic nitrification-aerobic denitrification strain with obvious denitrification effect was isolated from natural rubber processing wastewater.The 16S r RNA sequence of strain has 99%homology with Bacillus.And combined with the cell morphological characteristics,the strain is identified as Bacillus sp.,named JD-7.Then we explored different factors’effects on the denitrification capacity of JD-7.It was found that sodium succinate was the best carbon source for JD-7 and the strain had good ammonia nitrogen tolerance.The strain still grew well in the environment with the concentration of 1000 mg/L,and ammonia nitrogen removal rate can reach 54.02%.At the same time,the strongest nitrification ability was observed with temperature of30.35℃,initial p H of 7.85 and the C/N ratio of 6.13 by response surface analysis.Strain JD-7 has the ability to remove three kinds of inorganic nitrogen（NH₄⁺-N,NO₂^--N and NO₃^--N）,among which the ability to remove ammonia nitrogen is the strongest,up to 91.25%.And we found no nitrite accumulation during denitrification.The removal efficiency of nitrate nitrogen and nitrite nitrogen was 44.39%and 50.06%respectively.In the mixed nitrogen source,JD-7 would give priority to the use of ammonia nitrogen,followed by nitrate nitrogen.In order to cope with the complex water quality of natural rubber wastewater,we choose to use polyvinyl alcohol and sodium alginate as mixed carrier materials to immobilize bacteria.The result showed that when PVA concentration was 6%,SA was 2%,and Ca Cl2 was 4%,immobilized globule was the best condition.Strain JD-7 showed strong adaptability in the actual rubber wastewater,and the removal rate of ammonia nitrogen in the original wastewater could reach 131.48 mg/（L·d）.The nitrogen balance experiment showed that 7.55%of the initial nitrogen was converted to intracellular nitrogen,while 85.28%of nitrogen is removed in the form of gas.The functional enzyme gene analysis showed that the strain contained nitrate reductase gene,nitric oxide reductase gene and nitrous oxide reductase gene,which further proved that the strain had denitrification.In conclusion,heterotrophic nitrification-aerobic denitrification strain JD-7 has high nitrogen removal performance and can be used as a new strain in natural rubber wastewater treatment process.The culture conditions and denitrification characteristics of strains provide a theoretical basis for industrial application.The study of denitrification metabolic pathway and whole genome analysis can provide reference for further elaborating the denitrification mechanism of heterotrophic nitrification-aerobic denitrification strain.