Study On Biological Phosphorus Removal In AO Denitrification System And Its Mechanism

Traditional wastewater biological phosphorus removal is accomplished by Phosphate-accumulating Organisms(PAOs)through anaerobic phosphorus release and aerobic excessive phosphorus uptake.If biological phosphorus removal can be achieved in anoxic-aerobic denitrification system,biological denitrification and biological phosphorus removal process might be combined to simplify treatment process and develop a new biological phosphorus removal method.In this study,soluble starch was used as sole carbon source of synthetic wastewater under anoxic-aerobic condition and the phosphorus removal was studied.The microbiological mechanism of the new type of biological phosphorus removal was illuminated and the condition of biological phosphorus removal under biological nitrogen removal environment was proven.The study expended the understanding of biological phosphorus removal and laid a foundation for new process development.The main results and conclusions obtained from this study are as follows.1.In the anoxic aerobic SBR experiment system with starch as the sole carbon source,the nitrogen and phosphorus in the wastewater were both removed.Idle period had a significant effect on the phosphorus removal of the system.In the SBR system without idle period(i.e.,S1),the removal rate of phosphorus reached 70%,and no phosphorus release occurred during the whole operation cycle.When the idle time was 2 hours(i.e.,S2)and 4 hours(i.e.,S3)respectively,the removal rate of phosphorus in the S2 and S3 were both higher than that of S1,which reached 75% and 90%,respectively.Under the two idle conditions of the S2 and S3,phosphorus releases occurred during the idle phase,which were similar to that of a traditional phosphorus removal system.It implied the process of phosphorus removal in these systems was different under different operation based on idle time.There were also significant differences in microbial population structure among the three systems.In the S1,fermentative bacteria were the dominant group.In the S2 and S3,Proteobacteria and Bacteroidetes were dominant.Therefore,microflora structure determined the way of phosphorus removal in the three systems.2.The effective removal of nitrogen and phosphorus in wastewater was also achieved in the anoxic-aerobic continuous flow experimental system with starch as sole carbon source.The dissolved oxygen level had an important effect on the phosphorus removal efficiency of the continuous flow system.When dissolved oxygen was controlled at 0.5 mg/L in the aerobic tank,the phosphorus removal rate was around 75%,and the sludge sedimentation was good.When the dissolved oxygen was controlled at 2 mg/L in the aerobic tank,the phosphorus efficiency of the system was reduced to 53%,meanwhile,the sludge sedimentation became worse and the system became unstable.In the sludge of the system,the dominant bacteria were fermentative bacterium and Proteobacteria.Under different dissolved oxygen,the microbial structure were significantly different,some dominant species such as Microbacterium lacticum,Plasticicumulans acidivorans etc.under the DO of 0.5 mg/L,were vulnerable or disappeared under the higher dissolved oxygen of 2 mg/L.3.The metabolic process of 13C-labelled starch in the SBR system was tracked by nuclear magnetic resonance(NMR)technology.The results showed that the starch in the anoxic period,firstly was hydrolyzed into glucose by microbial cells,and then part of the glucose was fermented into lactic acid and secreted to the outside of the fermented bacteria,the other glucose was converted into glycogen stored in the cell.Under the condition without enough carbon sources in bulking liquid,this part of the intracellular glycogen could be converted to lactic acid and secreted into extracellular environment.4.Mechanism of the phosphorus removal was put forward.The fermentation bacterium in the anoxic-aerobic system could convert glycogen via the EMP pathway into lactic acid under the anoxic condition,and ATP was produced coupling the fermentation of glycogen to lactic acid.Fermentation bacteria used the ATP to complete the phosphorus accumulation.At the same time,the traditional PAOs in the system took the extracellular lactic acid into the cell and converted into glycogen and stored in the cell.In the aerobic stage,the traditional PAOs produced ATP,via decomposition of the glycogen under aerobic condition,which was then used to synthesize polyphosphate.Thus,the phosphorus removal during the whole anoxic aerobic period in the system was achieved.