Alginate-like Exopolysaccharides Research Articles

Accelerated aerobic granulation using alternating feed loadings: Alginate-like exopolysaccharides

Alginate-like exopolysaccharides (ALE) likely contribute markedly to strength of aerobic granules. This study cultivated aerobic granules from propionate wastewaters using strategies with different organic loading rates (OLRs) (4.4–17.4kg/m3-d). When the OLR increased suddenly, the constituent cells (Pseudomonas, Clostridium, Thauera and Arthrobacter) were stimulated to secret extracellular cyclic diguanylate (c-di-GMP) and produced excess ALE, which formed a large quantity of sticky materials that served as the precursor of aerobic granules. Formation of excess ALE was the prerequisite for accelerated granulation. Conversely, this study observed no enrichment of poly guluronic acid blocks in ALE during granulation.

The chemical and mechanical differences between alginate-like exopolysaccharides isolated from aerobic flocculent sludge and aerobic granular sludge

This study aimed to investigate differences in the gel matrix of aerobic granular sludge and normal aerobic flocculent sludge. From both types of sludge that fed with the same municipal sewage, the functional gel-forming exopolysaccharides, alginate-like exopolysaccharides, were isolated. These two exopolysaccharides were chemically fractionated, and investigated by FT-IR spectroscopy. The isolated polymers were made into a gel by calcium addition and the mechanical properties of these reconstituted gels were measured by a low load compression tester. The viscoelastic behavior of the gels was described by a generalized Maxwell model. The alginate-like exopolysaccharides derived from aerobic granules had significantly higher amount of poly(guluronic acid) blocks but lower amount of poly(guluronic acid-manuronic acid) blocks in the chemical structure, while the alginate-like exopolysaccharides derived from aerobic flocculent sludge had equal amount of poly(guluronic acid) blocks and poly(guluronic acid-manuronic acid) blocks. These differences result in a perfect gel-forming capability of alginate-like exopolysaccharides derived from aerobic granules and bestowed this exopolysaccharides gel a stronger mechanical property as compared to alginate-like exopolysaccharides derived from aerobic flocculent sludge. The different chemical and mechanical properties of these two exopolysaccharides contributed to the distinguished characteristics between aerobic granular sludge and aerobic flocculent sludge.

The contribution of exopolysaccharides induced struvites accumulation to ammonium adsorption in aerobic granular sludge

Aerobic granular sludge from a lab-scale reactor with simultaneous nitrification/denitrification and enhanced biological phosphorus removal processes exhibited significant amount of ammonium adsorption (1.5 mg NH 4 +–N/g TSS at an ammonium concentration of 30 mg N/L). Potassium release accompanied ammonium adsorption, indicating an ion exchange process. The existence of potassium magnesium phosphate (K-struvite) as one of potassium sources in the granular sludge was studied by X-ray diffraction analysis (XRD). Artificially prepared K-struvite was indeed shown to adsorb ammonium. Alginate-like exopolysaccharides were isolated and their inducement for struvite formation was investigated as well. Potassium magnesium phosphate proved to be a major factor for ammonium adsorption on the granular sludge. Struvites (potassium/ammonium magnesium phosphate) accumulate in aerobic granular sludge due to inducing of precipitation by alginate-like exopolysaccharides.

Characterization of alginate-like exopolysaccharides isolated from aerobic granular sludge in pilot-plant

To understand functional gel-forming exopolysaccharides in aerobic granular sludge, alginate-like exopolysaccharides were specifically extracted from aerobic granular sludge cultivated in a pilot plant treating municipal sewage. The exopolysaccharides were identified by the FAO/WHO alginate identification tests, characterized by biochemical assays, gelation with Ca 2+, blocks fractionation, spectroscopic analysis as UV-visible, FT-IR and MALDI-TOF MS, and electrophoresis. The yield of extractable alginate-like exopolysaccharides was reached 160 ± 4 mg/g (VSS ratio). They resembled seaweed alginate in UV-visible and MALDI-TOF MS spectra, and distinguished from it in the reactions with acid ferric sulfate, phenol-sulfuric acid and Coomassie brilliant blue G250. Characterized by their high percentage of poly guluronic acid blocks (69.07 ± 8.95%), the isolated exopolysaccharides were capable to form rigid, non-deformable gels in CaCl 2. They were one of the dominant exopolysaccharides in aerobic granular sludge. We suggest that polymers play a significant role in providing aerobic granular sludge a highly hydrophobic, compact, strong and elastic structure.