Intracellular Polymers Storage And Nitrogen, Phosphate Removal Of Granular Sludge In Anaerobic-Aerobic SBR

Granules mainly containing glycogen accumulating organisms(GAOs) were cultivated successively and stably existed in three sequencing batch reactors(SBR), inoculated by floclike activated sludge and fed with glucose(G), glucose-acetate(GA) and acetate(A) as organic substrate respectively, by means of special alternating anaerobic-aerobic operation mode, i.e. withdrawal after anaerobic period and sludge aeration during aerobic period to suppress the activity of phosphate accumulating organisms (PAOs). Optical and environment scan electron microscope examination showed that the morphology of granules were nearly spherical or elliptical with dense structure and clear outline. The average diameters of G,GA and A granular sludge were 896,802,1153μm respectively, and the maximal diameter was up to 2000μm. G,GA and A granular sludge had excellent settleability, and SVI were about 20~30ml/g.Considering sludge granulation process and physicochemical, biological characteristics of granular sludge, a model for the sludge granulation was proposed as consisting of the following steps: floclike sludge, dense floclike sludge, appearance of initial granules, growth of granules, dominance of granular sludge, granular sludge mature and granular sludge disintegration-regeneration. Moreover, it was suggested that main factors contributing to granular sludge formation were selective pressure, extracellular polymeric substances(EPS) and inorganic substances. Thereinto selective pressure, created by critical setting velocity, played an exterior role in selecting granules(fast setting biomass) and filaments and flocs(slow setting biomass). And EPS and inorganic substances maintained the structural integrity and accelerated the sludge granulation process by means of changing surface characteristics of bacteria and microbial aggregates. In addition, organic substrate composition, anaerobic feast and aerobic famine operation mode, organic loading rate and intermittent feeding strategy also affected the granular sludge formation and its characteristics and stability.Measuring and analyzing the variation of phosphate, organic substrate, intracellular glycogen and PHB in typical cycle in three SBRs, it was verified that the sort of organic substrate was strongly influenced the energy utilization mode, organics uptake rate and intracellular storage polymer component of GAOs. Moreover, results showed intracellular glycogen content was the key factor influenced anaerobic organics uptake amount and uptake rate. If intracellular glycogen content was below 0.05 g/gSS, anaerobic organics uptake efficiencies appeared to be dependent on glycogen content, and organics uptake efficiencies reached steady state as glycogen content was higher than 0.05 g/gSS. In addition, anaerobic organics uptake rate was in great difference with different glycogen content. Anaerobic organics uptake rate was increased with intracellular glycogen content increased during fast uptake period in initial anaerobic stage.Anaerobic-aerobic batch tests of GAOs granular sludge were carried out to investigate its simultaneous nitrification and denitrification(SND) performances under different TOC/N, results showed GAOs granular sludge had high SND activity, SND efficiencies were 96.4%,95.3% and 96.2% respectively as TOC/N were 5.0,4.0 and 2.8, and the total nitrogen removal efficiencies, decreased with TOC/N decreased, were 66.0%, 61.2% and 56.3% respectively. Moreover, resultsof anaerobic-anoxic and anaerobic-aerobic batch tests with nitrate and nitrite addition demonstrated GAOs, similar to PAOs, with the ability of denitrification, and intracellular storage polymer PHB was used as carbon source of denitrification and denitrifying glycogen accumulating organisms(DGAOs) were responsible organisms for the denitrification activity during SND process of GAOs.Granular sludge with the ability of simultaneous nitrification, denitrification and phosphate removal was cultivated by seeding GAOs granular sludge with SND potential,thus simultaneous organics, nitrogen and phosphate removal were achieved in single anaerobic-aerobic SBR. Cultivated granular sludge was 600~1000μm in diameter, SVI was 48ml/g, and TOC, ammonium nitrogen, total nitrogen and phosphate removal efficiencies were 90.0%, 99.3%, 85.5% and 95.6% respectively. Further batch tests results demonstrated intracellular PHB was used as carbon source of denitrification and denitrifying phosphate accumulating organisms(DPAOs) and glycogen accumulating organisms(DGAOs) were responsible for the denitrification activity during SND process. In addition, these results also showed that phosphate removal was accomplished by PAOs and DPAOs.