Characteristics Of LNA And HNA Bacteria Shuttling Between Flocs And Water Phase

According to the difference in cell size and intracellular DNA content,two types of bacteria are commonly found in nature,namely low-nucleic acid(LNA)and high-nucleic acid(HNA)bacteria.The biochemical properties of these two types of bacteria and their responses to changes in the external environment are also quite different.Changes in the two types of bacterial components can often predict changes in the quality of the water environment.However,the migration of LNA and HNA bacteria between flocs and water phase are not clear.In this study,the important denitrification process was selected as the research object,and the migration of LNA and HNA bacteria during the denitrification process were analyzed.The distribution characteristics of free-swimming bacteria under different denitrification conditions and their effects on the structure and activity of sludge floc were explored.At the same time,the related bacterial group gene sequencing analysis was carried out.The main results show as follow:(1)Free-swimming LNA and HNA bacteria constantly shuttle between the water phase and the sludge floc.Greater the denitrification rate resulted in a higher increase of free-swimming bacteria in the water phase,LNA bacteria get rid of sludge floc faster than HNA,and starch can capture free-swimming bacteria,HNA bacteria are more likely to be caught.The denitrification of sodium acetate had a more significant effect on free-swimming bacteria than the bridge-capture of starch.In periodic denitrification,LNA is more than HNA,while LNA is significantly lower than HNA in shock denitrification,mainly because long-term aerobic environment LNA bacteria are eluted.(2)Denitrification caused the sludge structure to show three stages of loosening,sloughing and erosion,and the sludge with better denitrification performance showed stronger loosening and sloughing.In the periodic denitrification experiment,the LNA /HNA increased during the loosening and erosion stages of denitrification,while the LNA / HNA decreased during the sludge sloughing stage,which indicate that LNA bacteria was mainly on the surface of flocs and functioned as glue or filling materials of the pores of flocs,and HNA bacteria functioned as a backbone of flocs,the gas produced by denitrification enhances the effective shuttle of the LNA.The change of sludge particle skewnesss can estimate the type of floc and the location of denitrification.And continuous or intermittent denitrification can not only enrich the species of denitrifying bacteria,but also improve the heterogeneity of flocs,ensuring that all flocs can promote denitrification.(3)The addition of free-swimming bacteria during aeration and denitrification will have a significant impact on the respirogram space and increase the respiration rate,especially the on-site specific respiration rate SOURs,the quasi-endogenous specific respiration rate SOURq,and the sludge recovery index RI value.However,the short-term increase in RI value after denitrification will not accumulate,and the system will recover on its own.SOURq is mainly driven by the structure of sludge,LNA /HNA can characterize the changes in the structure of sludge,while SOURe and RI are mainly driven by shuttling of LNA.(4)HNA bacteria have a high dependency on nutrients and belong to eutrophic bacteria,which change significantly with changes in nutrients,so HNA bacteria concentration can characterize the degree of pollution of water bodies.Ultrasound experiments have further proved that HNA bacteria functioned as a backbone of flocs,and sludge is the main carrier for removing pollutants.(5)HNA bacteria had higher abundance and diversity than LNA bacteria,it was the main functional bacteria and play an important role in removing nitrogen and phosphorus.The LNA bacteria are mainly anaerobic bacteria and do not have strong nitrogen removal ability.However,LNA bacteria can respond faster to denitrification and can be used as a signal for denitrification initiation.