| In Denitrifying phosphorus removal technology,Denitrifying Polyphosphate Accumulating Organisms(DPAOs)are used in alternating anaerobic/hypoxic conditions with NO2-/NO3-instead of traditional oxygen as electron accepers.Simultaneous removal of nitrogen and phosphorus was realized.In this process,the intracellular poly-?-Hydroxyalkanoates(PHA)stored in anaerobic phase is used as electron donor to complete phosphorus absorption and denitrification at the same time,which has the characteristics of"one carbon and two uses".Therefore,a new way for simultaneous nitrogen and phosphorus removal of low C/N wastewater has been opened up.In practical engineering applications,the metabolic mechanism of Polyphosphate Accumulating Organisms(PAOs)is affected due to the fluctuation of influent water quality,resulting in unstable phosphorus removal effect.In this study,sequential batch reactor(SBR)was used to investigate the metabolic mechanism of systematic denitrifying phosphorus removal bacteria under different influent phosphorus concentrations.The main research results are as follows:In the first stage,PAOs was enriched in alternated anaerobic and aerobic operation conditions,and the metabolic mechanism of PAOs was revealed in anaerobic and phosphorus-rich conditions by anoxic experiments.After 8 days of cultivation and acclimation,the anaerobic phosphorus release amount of the system increased from14.9mg·L-1to 55.3mg·L-1,indicating that the proportion of cohesive phosphorus bacteria in the system gradually increased.After 15 days of acclimation,the phosphorus release amount reached 69.8mg·L-1,and the phosphorus removal rate stabilized at 90%.PAOs gradually became the dominant population.After 21 days of operation,the amount of anaerobic phosphorus release decreased significantly,which may be due to the incomplete release of phosphorus due to the increasing demand for COD with the continuous enrichment of PAOs.In order to verify the above speculation,the influent COD was increased to 600mg·L-1on the39th day,and the anaerobic phosphorus release increased from 24.0mg·L-1to 90.3mg·L-1for30min,indicating that the lack of organic substrates would limit PAOs synthesis of PHA,leading to incomplete phosphorus release.In addition,a series of experiments on the emergency metabolic mechanism of PAOs under the conditions of phosphorus starvation and phosphorus starvation showed that:(1)PAOs without anoxic phosphorus uptake domestication can use NO2-as electron acceptor for denitrifying phosphorus uptake;(2)PAOs can reduce NO2-in the absence of phosphorus,which means that PAOs may initiate the stress metabolism mechanism from phosphorus metabolism to glucose metabolism in the absence of phosphorus.However,in the phosphorus-rich condition after phosphorus starvation,PAOs used NO2-as electron acceptor for denitrification and phosphorus absorption,indicating that its metabolic mechanism changed from glucose metabolism to normal phosphorus metabolism.The pilot experiment prelimatively concluded that PAOs had the possibility of stress metabolism.In the second stage,the enriched PAOs were acclimated with NO2--N as electron acceptor to obtain DPAOs.After the stable operation of the system,the influence of influent phosphorus concentration on the denitrifying phosphorus removal performance of the system and the conversion and utilization of carbon sources were evaluated through different phosphorus loads and phosphorus deficiency experiments for a long time.According to the removal performance of NO2-at different phosphorus concentrations,it can be found that in the case of phosphorus deficiency(working condition?,influent P=2mg·L-1),NO2-is fully utilized in the anoxic stage in the early stage without accumulation,indicating that when the concentration of NO2-is high and exposed to the system in a short period,due to the lack of phosphorus,DPAOs only uses PHA stored in the anaerobic phase to reduce NO2-to detoxify and not absorb phosphorus.However,the average accumulation of NO2-reached 5.1mg·L-1in the later stage,and the phosphorus removal performance of the system was weakened,indicating that the long-term addition of high concentration of NO2-under the condition of phosphorus deficiency produced certain biological toxicity to DPAOs.However,the average accumulation of NO2--N was 1.7mg·L-1and 1.1mg·L-1at the late stage of?(influent P=5mg·L-1)and?(influent P=10mg·L-1),and the phosphorus removal performance remained stable all the time,indicating that NO2-addition did not cause toxicity and inhibition to the microorganisms in the system.According to the sludge performance,with the increase of phosphorus concentration in the influent,the poly-P value in the sludge increased from12.4 to 280.0mg·L-1,MLVSS decreased from 3179 to 2033mg·L-1,and the biomass in the system gradually decreased and the biological activity gradually decreased.According to the variation law of typical periodic pollutants under different phosphorus concentrations,HAc absorption,PHA synthesis and Gly consumption all reached the maximum in the phosphorus deficient state,and the utilization of carbon source was more full,suggesting that DPAOs may have initiated the stress metabolism mechanism or the change of system flora structure led to the stoichiometric changes.According to the typical cycles of working conditions?and?,phosphorus metabolism takes precedence over glucose metabolism in the presence of phosphorus,and the presence or absence of NO2--N and PO43--P does not limit the degradation of PHA,indicating that the degradation of PHA occurs first in the process of hypoxic phosphorus uptake metabolism.In addition,the variation rule of typical pollutants in the working condition?(influent P=20mg·L-1)found that the absorption of PO43--P in the anoxic stage of 55.3mg·L-1required 10mg·L-1NO2--N as the electron acceptor for denitrifying phosphorus absorption,while in the working condition?(influent P=40mg·L-1),due to the excessive load of influent phosphorus,the insufficient addition of electron acceptor in the hypoxic section resulted in the coordination of NO2-and oxygen electron acceptor in the phosphorus absorption process,but the storage of poly-P was not affected.In the third stage,active sludge rich in DPAOs was used as the research object to evaluate the influence of different phosphorus concentrations on the stoichiometry of highly enriched DPAOs,and to analyze the influence of different phosphorus concentrations in influent water on the distribution characteristics of microorganisms,so as to explore the metabolic mechanism of Accumulibacter bacteria involved in phosphorus removal.High-throughput sequencing results show that when influent phosphorus is 2mg·L-1,Accumulibacter abundance in DPAOs is 92%,indicating that low phosphorus concentration can still be highly enriched in DPAOs.When the phosphorus concentration is 40mg·L-1,the species richness in the community is slightly decreased,but the population uniformity is slightly increased,and the Accumulibacter abundance is increased to 98%.With the increase of influent phosphorus concentration,the phosphorus release amount increased from5.9mg·L-1to 107mg·L-1,and the specific phosphorus release rate increased from 3.14 to 35.1mg·(g VSS·h)-1.Working condition?Due to the limited NO2-electron acceptor,the post-aeration process becomes the main period of phosphorus absorption,that is,from anoxic metabolism to aerobic metabolism,and the aerobic phosphorus absorption rate is faster than the denitrifying phosphorus absorption rate.The results of this study showed that DPAOs stress metabolism was mainly manifested as:(1)Under the condition of phosphorus deficiency(working condition?),the energy generated by poly-P degradation could not meet the anaerobic absorption of HAc by DPAOs and storage of PHA.At this time,DPAOs would use Gly degradation to provide energy,that is,switch from phosphorus metabolism to glucose metabolism.When the concentration of NO2-is too high and the inhibition effect is produced in the anoxic stage,DPAOs only uses PHA to reduce NO2-to detoxify but does not absorb phosphorus,and its metabolic mechanism also changes to glucose metabolism;(2)Under phosphorus rich conditions(working conditions?and?),the energy generated by poly-P degradation in the anaerobic stage can fully satisfy HAc's absorption and storage of PHA,while Gly hardly degrades.In the anoxic stage,PHA is used to reduce NO2-and absorb phosphorus,and the whole process is phosphorus metabolism;(3)In the presence of phosphorus(working conditions?and?),in the anaerobic stage,the energy absorbing HAc generated by poly-P degradation was firstly used and PHA was stored,while Gly was almost not degraded.When poly-P was cleared,Gly degradation was utilized to provide energy.In the anoxic stage,PHA was firstly used to reduce NO2-and absorb phosphorus.When no phosphate is available for absorption by DPAOs,only PHA is used to reduce NO2-.DPAOs in both anaerobic and anoxic stages have both phosphorus metabolism and glucose metabolism,which can be described as a transition behavior from glucose metabolism to phosphorus metabolism of DPAOs. |
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