[Action Mechanism of Bacillus on Microalgae During Nitrogen Metabolism in Urban Tailwater]

To improve deep denitrification of black and odorous water and improve the quality of surface water, we studied the characteristics of nitrogen metabolism and denitrification of urban tailwater by microalgae (Z), Bacillus (Y), and Bacillus microalgae (ZY). The results showed that there was a good removal effect of ammonia nitrogen of group Z and group ZY in urban tailwater. The degradation rate of both groups reached 95%. The best effect on the removal of nitrite nitrogen was of group Z in urban tailwater. The combined action of Bacillus and Micrococcus played a relatively strong and stable effect on the conversion of nitrite nitrogen to nitrate nitrogen in the nitrogen cycle reaction. Bacillus could effectively remove nitrate nitrogen and improve the removal efficiency of nitrate nitrogen by microalgae. Best removal effect of nitrate nitrogen was observed in group ZY in urban tailwater, with a degradation rate as high as 99%, in which the nitrate nitrogen was removed almost completely. The Bacteria with high proportions in Z were Chroococcidiopsis_PCC_7203 (24.38%), uncultured_bacterium-g_norank_f_A4b (23.65%), Exiguobacteriu (7.09%), Leptolyngbya_PCC-6306(9.41%), and Bacillus (1.99%). The bacteria with high proportions in ZY were Brevibacillus (22.94%), Clostridium (8.78%), and Bacillus (4.88%), and the proportion of Chroococcidiopsis_PCC_7203 was only 7.84% in ZY, which was considerably lower than that in Z samples. The conclusions were as follows:microalgae could effectively remove ammonia nitrogen in the system. Bacillus and microalgae had very good removal effect of ammonia nitrogen and nitrate nitrogen. During the nitrogen removal of black and odorous water by algae, the Bacillus inhibited the excessive growth of microalgae and prevented eutrophication and black odor in water. This study can provide data support for the deep treatment of urban tail water and prevention of surface water eutrophication.