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Research On Rapid Cultivation Of Aerobic Granular Sludge And Its Characteristics In Biological Nutrient Removal

Posted on:2009-06-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q YangFull Text:PDF
GTID:1101360242990777Subject:Environmental Engineering
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Aerobic granular sludge is self-aggregated bio-particles by microorganisms under certain conditions, which has compact structure, good settling ability and perfect biological activity. Because of the mass transfer limit induced by the complex structure and big particle size of granular sludge, there could be different kinds of oxygen and substrate conditions in single granule, which could be propitious to various microorganisms. So different metabolism could simultaneously happen insider of granules, which makes the aerobic granular sludge become a perfect carrier realized the simultaneous biological nutrient removal. Based on the successful cultivation of aerobic granular sludge, effects of different seed sludge and addition of Mg2+ to the rapid cultivation of aerobic granular sludge was investigated in this study. At the same time, the start-up of aerobic granules SBR was accomplished. The main projects were focused on the characteristics and performances of simultaneous nitrification and denitrification (SND) and simultaneous nitrogen and phosphorus removal of aerobic granular sludge. The mechanisms of biological nutrient removal were analyzed and the effects of operational parameters to the aerobic granules SBR were discussed in this paper.According to the prophase works on the cultivation of aerobic granular sludge with simultaneous nitrification and denitrification ability from activated sludge, the advanced addition of 15% (by weight) aerobic granules, and the enhancement of hydraulic selection, optimization of aeration and adjustment of carbon source accelerated the formation of aerobic granules, especially the granules with bigger size, in SBR. It took about 15 days from the inoculation to the complete aerobic granulation when the granules with the particle size over 0.34mm were greater than 50% in reactor. Compared to the average particle diameter of 0.281mm in reactor inoculated activated sludge, the average particle diameter in reactor inoculated 15% aerobic granules was 0.426mm. The addition of little mature aerobic granules before cultivation and increase of Mg2+ concentration in influent also promoted the secretion of extracellular polymeric substances (EPS) in sludge, which changed the superficial property of sludge and quickened the aggregate of sludge. So the compact aerobic granular sludge could form rapidly in SBR under the conditions above.Aerobic granules SBR had been stably operated for 65 days, and it showed good SND nitrogen removal performances and the ability to withstand shock loading. COD, ammonium nitrogen and total nitrogen removal efficiencies were higher than 90%, 80% and 75% respectively. Because of the diffusion limit of oxygen and substrate in granule, the composition of microorganisms, concentration distribution of substrate, metabolism and biochemical reaction existed difference in different zone of granule. The difference constructed the favorable micro-environment where SND nitrogen removal could be achieved. The outstanding characteristic of aerobic granules SBR was the total nitrogen removal in aerobic condition, 75.9% of total nitrogen was removed in this phase, at the same time, the concentration of NOx only increased 1.9 mg/L and the accumulation of NOx hadn't happened. During anaerobic period, organic substrate was mostly absorbed and stored as intracellular polymer (Poly-β- Hydroxybutyrate, PHB), and nitrogen was removed via SND in which the intracellular storage polymer PHB was as the denitrification carbon source during successive aerobic period. Further batch tests revealed that the variation of ammonium nitrogen removal efficiencies was unconspicuous with influent C/N decreased, but the total nitrogen removal efficiencies decreased for lack of denitrification carbon source.Lower dissolved oxygen (DO) concentration was in favor of the present of anoxic/anaerobic zone in granules, which provided advantageous survival and reaction environment for denitrifying bacterium, decreased the accumulation of nitrate nitrogen and improved the performances of SND nitrogen removal.The denitrifying phosphate accumulating organisms in aerobic granular sludge could be enriched with the sodium acetate as carbon source domesticated under anaerobic/aerobic model for 30 days. The percentage of denitrifying phosphate accumulating organisms in poly-phosphate-accumulating organisms in granules increased from 39.91% to 54.87% through domestication. The aerobic granular sludge SBR showed good simultaneous nitrogen and phosphorus removal performances.When the influent concentration of phosphate was 8~12 mg/L during domestication, the effluent concentration of phosphate decreased from 3.2 mg/L at the beginning of to 1.2 mg/L at the end, accordingly, when the influent concentration of total nitrogen was 30~40 mg/L, the total nitrogen removal efficiencies increased from 46.4% to 63.6%. Based on the special aerobic/anaerobic (anoxic) layered structure of aerobic granule, the simultaneous nitrogen and phosphorus removal by aerobic granular sludge was achieved through the carbon cycle as the center and surrounding the metabolism of intracellular storage polymer PHB, namely, organic substrate was mostly absorbed and stored as PHB companied by phosphate release during anaerobic period, and nitrogen and phosphate were removed via PHB driven SND phosphate removal during successive aerobic period. PHB not only was for the aerobic phosphate uptake with the oxygen as electron acceptor by aerobic poly-phosphate- accumulating organisms at outsider of granules, but also used as carbon source for denitrification and denitrifying phosphate accumulating with the nitrite as electron acceptor by the denitrifying bacterium and denitrifying phosphate accumulating organisms insider of granules. The additional anoxic phase after anaerobic/aerobic model was unnecessary to the simultaneous nitrogen and phosphorus removal by aerobic granular sludge. The anaerobic/aerobic model with 2h anaerobic phase and 4h aerobic phase could ensure the perfect performances of biological nutrient removal. The influence of DO to the performances of simultaneous nitrogen and phosphorus removal in aerobic granular sludge SBR was exhibited by the compression of anoxic one in granule and the lower DO was benefit to the stable operation of systems. With the decrease of influent C/N, the short of PHB stored in anaerobic phase led to the competition between aerobic phosphate uptake and denitrifying phosphate accumulating and the decrease of simultaneous nitrogen and phosphorus removal performances. The control of sludge retention time in aerobic granules SBR should consider from the balance of sludge discharge for phosphate removal and sludge retention for keeping the stable operation of systems.Aerobic granules SBR had been stably operated under anaerobic/aerobic for 120 days, and the perfect pollutant simultaneous removal performances kept during the operation process. organics, total nitrogen and phosphate removal efficiencies were higher than 95%, 85% and 95% respectively. At same time, the systems showed good ability to withstand fluctuant loading and stability to long-term operation. Research showed aerobic granules SBR technics was an advanced wastewater treatment technology especially for the nitrogen and phosphorus removal of municipal wastewater with lower organic pollutant.
Keywords/Search Tags:Aerobic granular sludge, Biological nutrient removal, Sequencing batch reactor (SBR), Extracellular Polymeric Substances (EPS), Simultaneous nitrification and denitrification (SND), Denitrifying phosphate accumulating organisms (DPAOs)
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