Nitrogen Removal Performance And Mechanism Of Bacillus Sp.K5

In recent years,with the rapid development of industry,agriculture and aquaculture,the accumulation of nitrogen in water has seriously damaged the environment and threatened human health.How to effectively remove nitrogen in water has attracted extensive attention.Bacillus sp.K5,isolated from a large-scale bioreactor,was used as an experimental strain in the current study.The denitrification performance was analyzed and the corresponding mechansisms were explored through isotope analysis and enzyme purification.Afterwards,K5 strains were immobilized to treat nitrogen-containing waster water including piggery wastewater and nitrite-containing wastewater,with a view to lay a solid foundation for the application of K5 on real wastewater treatment.Firstly,the effects of different carbon sources,C/N ratio,initial concentration of nitrogen and pH on the nitrification and denitrification performance of Bacillus sp.K5 were investigated.Important conclusions are drawn as follows:?1?Bacillus sp.K5 did not accumulate nitrite during nitrogen removal,indicating that it has a good prospect for practical application in wastewater treatment;?2?The optimal carbon source was demonstrated to be sodium citrate,and the optimal C/N ratio and pH were 15 and 7.5,respectively.Moreover,a relatively high concentration of ammonium or nitrite could be completely consumed by Bacillus sp.K5,indicative of excellent nitrification and denitrification performance.Secondly,some important intermediates such as hydroxylamine and nitrite were detected using the ¹⁵N isotope analysis during the process of nitrogen removal.Then,the key enzymes?hydroxylamine oxidase and nitrite reductase?involved in the process of nitrogen removal were purified.On the basis of enzymology characteristics,the strain K5 was speculated to have a complete nitrogen removal pathway:nitrification of ammonia nitrogen to nitrite by ammonia monooxygenase and hydroxylamine oxidase,followed by denitrification of nitrite to gaseous products by nitrite reducase.Finally,in order to further improve the nitrogen removal efficiency,Bacillus sp.K5 was immoblilzed with sodium alginate-activated carbon to explore the intermittent and continuous treatment capacity of Bacillus K5 when treating real piggery wastewater?RPW?and nitrite-containing wastewater.Batch experiments showed that the immobilization could make the strain K5 more active and withstand a higher concentration of pollutants,whereas immobilized K5 strains packed in a fixed-bed reactor could contiuously remove ammonium or total nitrogen with removal efficiency being more than 90%.In addition,the fixed-bed reactor loaded with immobilized K5 is aslo effective in nitrite removal since up to 95.85mg/L of NO^-₂-N could be removed.All the above results indicate that Bacillus sp.K5 has great potential in the real wastewater treatment.