Study On The Performance Of BBSNP Process And Phosphorus Removal Characteristics Of Denitrifying Polyphosphate-accumulating Organisms

Excessive phosphorus-rich waste water discharged into the river has beenconsidered to be the most important reason to cause―eutrophication‖, withincreasingly stringent discharge standards of national urban sewage, phosphorusremoval was highly concerned. From cost-effective, energy saving andenvironmental friendly point of views, biological phosphorus removal is the bestoption, since not only it can save the consumption of considerable chemicals, butalso can avoid the secondary contamination of the chemical sludge, expectially itpossess biological sustainability. However, the majority of our existing waste watertreatment plants can’t achieve the latest phosphorus discharge standard （＜0.5mg/L）.In particular, a lot of urban waste water characteristic with inadequate carboncource, resulting in the imbalance of C, N and P, thus it is different to achievesimultaneous nitrogen and phosphorus removal. Considering this, it is most pressingmatter of the moment to explore a high efficiency, low consumption biologicalphosphorus removal technology, luckly denitrifying dephosphatation technologyseemingly could offer the possibility though marginal engineering applications.On the basis of the denitrifying dephosphatation theory and A/O process,Bi-Bio-Selector for Nitrogen and Phosphorus removal process （BBSNP process）was developed. It can effectively solve the effect of nitrate in recycled sludge onanaerobic phosphorus release, and achieve simultaneous nitrogen and phosphorusremoval through denitrifying phosphorus accumulating organisms （DPAO）so-called―dual use of the carbon source‖. Moreover, this process can effectivelycontrol sludge bulking.In this study, denitrifying phosphorus and nitrogen removal performance ofBBSNP process was systematically studied with real urban wastewater at room andlow temperatures, the population distribution and microbial diversity of differentperiods were traced by molecular biology methods（FISH and DGGE）, dynamicassociation between the main functional bacterium was evaluated and the mainrunning factors were also studied. The results show that the most suitable operatingparameters in BBSNP process were100%of SRT,150%of mixed liquor recycle ratio,200%of nitrified liquor recycle ratio and DO of1.0¹.5mg/L; the COD,nitrogen and phosphorus removal efficiency of BBSNP process treating low C/Nwastewater at room temperature was89%、90%and97%, respectively, which canmeet the Grade A standards of urban sewage treatment plant emission standards（GB18918-2002）. However, nitrogen removal peformance was highly influenced bylow temperature. In addition, less than50mg/L of anoxic COD concentration didnot cause the competition between ordinary denitrifying bacteria and DPAO, anoxicnitrate and anoxic P-uptake have a good linearship,1mg NO₃^--N consumptioncorresponding to1.8mg TP absorbtion, which can be used as one of the importantparameter in BBSNP system.The main phosphorus accumulating organisms in BBSNP process are DPAO,Hence, phosphorus removal characteristics, main influencing factors, competitionrules, sludge characteristic and metabolic stoichiometry of DPAO were furtherinvestigated in anaerobic/anoxic and anaerobic/aerobic environments. Theexperimental results show that anoxic denitrifying dephosphatation inanaerobic/anoxic environment contributed by the cooperation of PAO I, PAOII andDGAO when acetate as carbon source, where PAO I and DGAO reduced nitrate tonitrite, thus both PAO I and PAO II can use nitrite as electron acceptor of anoxicP-uptake, PAO I also can directly utilize nitrate as well. Mg/Ca molar ratios havesignificant impact on the formation of EPS gel, when the molar ratio of Mg/Ca≥5.0,the sludge can not provide a good carrier for the growth of DPAO/PAO since EPSgel formation has been severely damaged, resulting in the deterioration ofphosphorus removal. Under both room and low temperature, the competitionbetween Accumulibacter subclades do not influence the phosphorus removalefficiency, however, the anaerobic P/HAc ratios in so highly enrichedAccumulibacter cultures are significantly lower than in PAO models,suggesting thePAO model should be modified. In addition，low temperature have potentiality tosuppress the proliferation of GAO, and to some extent inhibit PAO II undershort-term conditions, while PAOII have a competitive advantage than PAOI underlong-term conditions. The granule sludge in low temperatue produced considerableamount of alginate-like EPS, which makes the gradule sludge regular morphology,big particle size and stronger mechanical strength. Regardless poly-phosphate is limited or not, PAO II can behave as GAO metabolism anaerobically and behave asPAO metabolism aerobically, but PAO I always behave PAO metabolism （not GAOmetabolism） under both anaerobic and aerobic conditions.