Start-Up And Enhancement Of Simultaneous Nitrification, Denitrification And Phosphorus Removal System Based On Aerobic Granular Sludge In The Anaerobic/Oxic/Anoxic Mode

Environmental pollution related to wastewater treatment has become a growing concern as the rapid development of urbanization.Increasingly stringent environmental regulations have also been imposed for urgent demand for advanced and effective approaches for wastewater treatment.Biological nitrogen and phosphorus removal have been widely used as their effectiveness,cost-efficiency and environementally-friendy advantanges.More and more developing technologies have been exploited based on the conventional nitrogen and phosphorus removal mechanisms,including denitrifying phosphorus removal,simultaneous nitrification and denitrification?SND?,partial nitrification and denitrification?PND?,and anaerobic ammonia oxidization?ANAMMOX?.These newly developed techniques focus on the contradictions between nitrogen and phosphorus removal like competitions for carbon sources and sludge retention time?SRT?and so on.Among them the SND combined with enhanced biological phosphorus removal?EBPR?termed SNDPR is a promising alternative technology as the capacity for simultaneous nitrogen and phosphorus removal.Aerobic granular sludge technology is a newly developed technology for wastewater treatment and has become an alternative for conventional activated sludge processes recently.The aerobic granular sludge technology has also widened its application from lab-sacle tests to several full-scale plants.Compared with the conventional activated sludge,aerobic granules as the self-aggreates of microbial flocs owes the advantages of excellent settleability,high biomass retention,compact physiochemical structures,capacity to withstand high organic loading rates and toxic substances etc.Mature aerobic granules are compact particles with spherical or ellipsoid shape,and can be divided into several layers as the restirictions for oxygen and substances.Therefore,oxic microbes reside in the outer layer of granules for easily oxygen available,with anoxic and anaerobic microbes living inside for less oxygen and substances.Now the aerobic granular technology is growing fast both in the theoretical and applicational studies.Therefore,this work focuses on the construction and application of aerobic granules based SNDPR system in the anerobic/oxic/anoxic?A/O/A?mode.The mechanisms for aerobic granulation and nutrients removal were explored in terms of the long-term stability of aerobic granular SNDPR system and dynamics of bacterial communitites.The patterns for simultaneous nitrogen and phosphorus removal in the aerobic granular SNDPR system was revealed as well as several corresponding enchancement strategies.In addition,the long-term storage and subsequent reactivation of aerobic granules within the SNDPR system is also investigated.Below are the main objectives and results of the present work:An aerobic granular SNDPR system was developed in a sequencing batch reactor?SBR?operated in an A/O/A mode at low organic loading rate and the mechnisms for granulation were analyzed by pyrosequencing technology.Results revealed that aerobic granules could be achived in an 8-h-cycle SBR at an organic loading rate of 0.3 kg chemical oxygen demand?COD?/?m³·d?by lowering the settling time from 20 to 2 min.Aerobic granules were with a mean diameter of 1.2 mm,sludge volume index at 30 min(SVI₃₀)of 32 mL/g,specific gravity of 1.021 and mixed liquor suspended solids?MLSS?of 4831 mg/L.The newly formed aerobic granular SNDPR behaved effective removals for COD,nitrogen and phosphorus.Bacterial dynamics analsyis revealed that aerobic granulation was obtained with the cooperations of key microbes under suitable physiochemical conditions.Long-term operation of aerobic granular SNDPR system revealed the superb capacity for simultaneous C,N and P removal.Cycle performance at a typical period was studied to evaluate the capacity and mechanism for nutrients removal.COD was fastly absorbed at the first 1 h of anaerobic phase,accomplying with the extracellular denitrification of nitrite and nitrate residuals from the previous cycle and phosphorus release.Aerobic phase witnessed the fast nitrification process with considerable nitrogen loss due to SND,along with the luxury phosphorus uptake.Anoxic phase is necessary for extra nitrite/nitrate removal.Feasibility and mechanism of enhancement for SNDPR system is evaluated by changing the aeration time with as high aeration rate as the granulation process.Results showed that aeration time rarely influenced the stability of aerobic granules but reduced aeration time led to higher nitrogen removal efficiency.Enhanced nitrogen removal rates from 64.29 to 86.18%was achieved.Reduced aeration time stimulated the aerobic SND and favored the anoxic intracellular denitrification.Glycogen accumulating organisms?GAOs?were suppressed while phosphorus accumulating organisms?PAOs?,denitrifying PAOs?DNPAOs?and ammonia oxidizing bacteria?AOB?were enriched under lower aeration time.Aerobic granules running under extremely low superficial gas velocity?SGV?was comprehensively studied by changing the SGV from 0.17,0.11 to 0.04 cm/s.Enhanced nitrogen removal from 63.71,76.87 to 94.12%was achived with the gradually decreased SGV,along with effective COD and total phosphorus?TP?removals.The mechanism for enhanced SNDPR system performance lied in the enhancement of aerobic SND and nitrite accumulation rate?NAR?,combining with enhanced intracellular denitrification and phosphorus removal.The enrichement of AOB rather than nitrite oxidizing bacteria?NOB?ensured low-cost nitrification,while stimulation of PAOs instead of GAOs favored phosphorus removal.Mixed carbon sources by sodium aceatae?NaAc?and glucose were used to evaluate the feasibility of enhanced SNDPR system performances in the aerobic granular SBR.Results present that lower ratios of NaAc favored COD,nitrogen and phosphorus removals.Enhanced reactor performance by mixed carbon sources was due to the adjustment of carbon usage in the A/O/A mode.NaAc to glucose at 3:1 ensured highest carbon usage efficiency mainly the intracellular carbon transformation rate.Besides,mixed carbon sources altered the inner microbial compositions within the aerobic granular SNDPR system.58 d storage and subsequent reactivation processes were conducted after the stable operation.Aerobic granules could maintain their structural integrity and recovered soon in terms of color,settleability,microbial activity and nutrients removal rates.The aerobic granules adopted a relative hydrophobicity?RH?protection mechanism during the storage period and excessive extracellular polymeric substances?EPS?mainly PN were secreted for storage and reactivation.Illumina MiSeq sequencing results revealed that the multiple anaerobic microbes capable of withstanding the anaerobic and starving durations are the key forces for long-term storage and fast reactivation.