| According to traditional mechanism of phosphorus removal,excessive phosphorus uptake in aerobic condition is achieved through fully anaerobic phosphorus releasing.Phosphorus accumulating organisms?PAOs?mainly absorb volatile fatty acids to synthesize internal carbon source under anaerobic conditions,at the same time,the release of phosphorus completed.If anaerobic stage is absent or carbon source is macromolecular organics,it is difficult to achieve efficient phosphorus removal.Recently,it was demonstrated that phosphorus could be removed in anoxic aerobic SBR system with starch as sole carbon source.This study revealed the characteristics of phosphorus removal in the SBR system and analyzed the influence of different factors on phosphorus uptake.The paper was aimed at improving the biological phosphorus removal theory existing,and laying the foundation for further development of new high efficiency biological phosphorus removal technology.The main results obtained by this study are as follows:?1?In the anoxic-aerobic SBR system with starch as the sole carbon source,efficient nitrogen and phosphorus removal could be achieved after a period of induction and domestication,which was different from traditional phosphorus removal and denitrification phosphorus removal.?2?In anoxic-aerobic SBR system?R1?,the metabolic energy of microorganisms was from starch fermentation and phosphorus uptake was mainly accomplished in anoxic phase by fermentation bacteria that could produce lactic acid.In anaerobic-aerobic SBR system?R2?,phosphorus removal was mainly accomplished by phosphorus accumulating bacteria through aerobic excessive phosphorus uptake.?3?Compared anoxic-aerobic SBR system?R1?with anaerobic-aerobic SBR system?R2?,R1 was more beneficial to the growth and enrichment of Candidatus Saccharibacteria,Enterobacter and Lacibater,all of them could ferment glucose into lactic acid.In R2,the dominant bacteria were Thiothrix,Thermomonas,Chryseolinea.The microbial community was more complex in structure and much higher in biodiversity.?4?In the stable anoxic-aerobic SBR system,nitrite had an inhibiting effect on the absorption of phosphorus in anoxic stage,while it had a promoted effect on the release of phosphorus.When the concentration of NO2--N was 2mg/L,5mg/L and 10mg/L,respectively,the average rate of anoxic phosphorus release was 0.532,0.584 and 1.02mgPO43--P·gSS-1·h-1,and the average rate of aerobic phosphorus uptake was 0.462,0.365 and 0.357 mgPO43--P·gSS-1·h-1,that was,the average rate of anoxic phosphorus release increased and the average rate of aerobic phosphorus uptake decreased with the concentration of NO2--N increasing.During the anoxic stage,the concentration of lactic acid decreased and the content of glycogen increased with the increase of NO2--N concentration.It inferred that nitrite inhibited the process of lactic acid formation,resulting in the lack of energy for phosphorus absorption in anoxic stage,which affected the uptake of phosphorus.?5?The change of carbon source had a significant effect on phosphorus removal efficiency and mechanism:Lactic acid as the carbon source,microorganisms could directly utilize lactic acid to synthesize PHB and glycogen,and efficient biological phosphorus removal could be achieved.The mechanism of phosphorus removal was the same as that of traditional phosphorus removal.Mixed media as carbon source,the phosphorus removal rate was low,which proved that starch was the key factor to achieve anoxic phosphorus absorption. |
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