Studies On Bacterial Alginates In Aerobic Granules

Bacterial alginates were extracted from aerobic granules, identified by FAO methods and characterized by UV/visible Spectroscopy, Infrared Spectroscopy, solid state Nuclear Magnetic Resonance Spectroscopy, Mass Spectrometry, Powder X-ray diffractometry, Atomic Force Microscopy, Scanning Electron Microscopy, Transmission Electron Microscopy and elemental composition. Alginate content in aerobic granules is determined as 351mg sodium alginate/g SS. The extracted bacterial alginates are mixtures of partially O-acetylated oligosaccharides with M/G ratio 0.85. Under the inducement of CaCl2, they demonstrate different conformations under Atomic Force Microscopy analysis, transfer from randomly distributed globules, to rod-like and flower-shaped aggregations, finally to ordered weblike networks as their concentrations increased. They are capable of forming gel beads when dropped in multiple cation metal solutions.Ruthenium red staining was adapted in the study on extracellular polysaccharides distribution in aerobic granules. Both SEM and TEM observations manifested the existence of weblike alginate gel. The selfassembly property of bacterial alginate molecules has positive effect on increasing granules'specific gravity, particle size and settling velocity. The bacterial alginate gel matrix in the aerobic granule not only contributes to its improved setteability and enhanced solid/liquid separation capacity, but also offers bacteria the same inhabitancy and protection as the manmade alginate immobilizations do. During the period of filaments propagation, this alginate matrix aids in keeping high settling velocity and prevents sludge bulking.A procedure for spore quantification in aerobic granules was developed. Sporecontent was determined by analyzing dipicolinic acid (dpa) extracted from aerobicgranules. Results show that dpa constitutes 33.7 mg per g SS, meaning that about337mg per g SS were spores, not the normal vegetative cells. Aerobic granules couldrecover their metabolism activity in a very short time after sterilized at 121℃15psifor 15mins; frozen at -21℃for two weeks and exposed to UV light (30w) within thedistance of 30 cm for 1 hour, for the large amount of spores exist in the aerobicgranule, which are more capable to sustain the sever conditions than the normalvegetative cells.Pure culture aerobic granules, with outstanding low SVI, high settling rate andspecific gravity, were successfully developed by cultivating the strain selected fromthe mixed culture aerobic granules, in shaking Erlenmeyer flask by sequencing batchway. The strain was phenotypicly, biochemically and genotypicly identifiedbelonging to Bacillus cereus A. With the aerobic granule formation capability andpopularity in the environment, the genus Bacillus cereus A is required more attentionin biological wastewater treatment domain. Investigations on bacterial alginateextracted from pure culture aerobic granules prove that alginate gel is the maincomponent of aerobic granular sludge.Bacterial alginates were also extracted from activated sludge and biofilmcultivated in SBR, and anaerobic granules. Results show that activated sludge,biofilm, and anaerobic granules all contain certain amount of bacterial alginates.Similar with aerobic granules, bacterial alginates extracted from them are alsoO-acetylated oligosaccharides blends, which demonstrates that bacterial alginatesplayed an important role in bio-aggregations. Results of bacterial alginates characterization, spore content introduction and Bacillus cereus alginate secreting property will throw light on aerobic granules formation mechanism investigations.