Study On Conditions And Mechanism For Nitrogen Removal Of Ammonia Wastewater By Immobilized Denitrying Bacteria

Traditional biological nitrogen removal is composed of aerobic nitrification and anaerobic denitrfication.Because of the complicate operation and the high cost of traditional way,several new biological processes have been developed,such as anaerobic ammonium oxidation (Anammox),Single reactor system for High Ammonia Removal Over Nitrite process(SHARON),completely autotrophic nitrogen removal over nitrite process(Canon) and oxygen-limited autotrophic nitrification denitrification process(Oland).The experimental design of the process applied in this paper is to accumulate nitrite by ammonia-oxidizing bacteria(AOB),then transfer the nitrite to nitrogen by aerobic denitrifying bacteria immediately.The aerobic denitrifying bacterium FX preserved in the lab was identified.It showed 99%of similarity with Sphingomonas sp.and was named as Sphingomonas sp.CZ.Sphingomonas sp.CZ grows slowly and reaches logarithmic phase after seven days of culture.This strain could bear 8mg/L of dissolved oxygen in broth,and shows good ability to remove nitrogen.This study focused on the synergistic effect of nitrogen removal by ammonia-oxidizing bacteria Ochrobactrum sp.CZ and aerobic denitrifying bacteria Sphingomonas sp.CZ on the surface of calcium alginate gel beads.The synergistic nitrogen removal conditions such as salt concentration,pH,initial ammonia concentration and speed were studied.The results showed that the best conditions for the remove of nitrogen were as follows:nitrogen concentration of 50mg/L,pH=8,static culture.Lower pH of system showed inhibition effect on bacteria activity, higher pH is not conducive to calcium alginate gel beads.High dissolved oxygen is not conducive to the accumulation of nitrite.The biofilm of the two strains was also studied and observed under fluorescence microscopy after being dyed by a kind of nucleic acid dyestuff.Biofilm on calcium alginate gel beads under different environmental conditions was evaluated.It was found that high salt concentration and faster speed would destroy the biofilm or result in desorption of biofilm.The result showed that the number and structure of biofilm have correlation with the ammonia removal ability of bacteria.