The Effect And Mechanism Of A Variety Of Environmental Factors With Biological Phosphorus Removal In The Aerobic/Extended-idle Regime

Phosphorus is inevitably existed in the natural water environment andmeanwhile is also an important nutrition element of organisms. However, the highcontent of phosphorus in aquatic environment will cause eutrophication. Therefore，efficient and reliable Pi removal methods are urgently required to solve theincreasingly stringent problem of eutrophication．Although anaerobic/aerobic(A/O)process is widely applied in the realwastewater treatment plants，the stability and reliability of the process are still aproblem． Even operated under seemingly favorable operational conditions，deterioration in performance and even failures of A/O systems have been widelyreported in literatures due to external disturbances such as high rainfall，excessivenitrate loading to the anaerobic reactor,or nutrient limitation. On the other hand, theA/O process has higher requirements of VFA. When the VFA content in influent islack, a certain amount of VFA will be required to be added into wastewater to ensurethe normal operation of biological phosphorus removal, which thereby causing theoperation cost. This characteristic strongly hinders its application and generalizationin real wastewater treatment.The aerobic/extended-idle biological phosphorus removal process (AEI) is a newbiological phosphorus removal regime found by our team. This process can achievean excellent phosphorus removal without the anaerobic phase. In the previous study,we found that the AEI process was less dependence on VFA than the A/O process, anda good phosphorus removal could be still obtained using glucose as the sole carbonsource. If the AEI biological phosphorus removal process is well understood, aneconomically stable convenient biological phosphorus removal process might bedevelopped. Thus， to reveal the effect and related mechanism of several keyenvironmental factors (ie, pH, carbon source, aeration intensity and idle time) onbiological phosphorus removal involved in the AEI regime，this study conducts aseries of application basic researches financially supported by the National NaturalScience Foundation of China．The results show that the optimal pH of the AEI process is7.5±0.2with theaverage phosphorus removal efficiency of97.8%when testing under the three pHconditions (7.0±0.2，7.5±0.2，8.0±0.2). It is found that the AEI process showshigher adapatability to pH as compared with the A/O process. Although different phosphorus removal ability are detected under different pH conditions, theperformance of phosphorus removal in the AEI process is higher than that in the A/Oprocess under the same pH conditions. pH can affect the microbial cell surfaceelectric potential difference, thereby changing the relation of energy supply betweenthe phosphorus removal process. When the pH value is controlled at7.5±0.2, theactivities of PPK and PPX are highest, and the PAOs are also dominant in systems.When using acetate and propionate as the sole carbon source, good phosphorusremoval can be achieved in both reactors. The propionate-fed reactor requires longerdomestication period than acetate-fed reactor. When the acclimation time extendedthe activities of PPK and PPX are improved significantly in the propionate-fedreactor, and the PAOs was dominant in the competition with GAOs. In the aerobicphase the amount of glycogen synthesis was also decreased, so that the more energygenerated by hydrolysis in the system was used to poly-P synthesis, and leading tothe improved efficiency of phosphorus removal eventually.The effect of different aeration intensity on the AEI biological phosphorusremoval regime is evaluated. When aeration intensity is200L/h, the phosphorusremoval efficiency is higher than85%, and the system sludge settling properties isgood. With the increase of aeration rate to400L/h, the phosphorus removal efficiencyis higher than200L/h, but the sludge in this system changes into white and poorsettling is observed. Aeration in the AEI biological phosphorus removal process onthe one hand in the aerobic phase due to changes in the oxygen supply relationship,thereby affecting the the phosphorus removal process energy supply relationship, onthe other hand, affects the activity of PPX related to the phosphorus removalefficiency of the system.When the idle time is set at8h, the phosphorus removal efficiency is highest,with average phosphorus removal efficiency of95.18%. With the increase of the idletime, the PPX activity also increases which resulting in increased poly-P hydrolysisto provide a basis for the aerobic phosphorus uptake in next cycle. The increase ofidle phase benefits the phosphorus removal efficiency. If the reactor cycle is not setthe idle phase，the release of phosphorus by phosphorus removal microbes will occurin the next cycle of the aerobic phase, the microbe incell poly-P reach a certainconcentration will no longer increased and the phosphorus removal efficiency will topoor, and may even lose.Through in-depth analysis and discussion of the effect and related mechanism offour factors on AEI biological phosphorus removal process, the AEI biological phosphorus removal theory is deeply understood, which provides a theoretical basisand data support for the application of this regime.