Isolation and characterization of temperature and alkaline stable bioflocculant from Agrobacterium sp. M-503.

A bacterium isolated from activated sludge of propylene epoxide wastewater was identified as Agrobacterium sp. M-503. It was confirmed to produce bioflocculant with excellent flocculation activity. The yield of the bioflocculant reached 14.9 g/l in batch cultivation with a carbon source conversion of 74.5%. This bioflocculant was temperature and alkaline stable, retaining almost all flocculation activity after being treated at 121°C for 20 minutes or at pH 12.0. It consisted of neutral sugar, uronic acid, aminosugar and protein in weight ratios of 85.0:9.9:2.1:3.0. The active polysaccharide fraction of the bioflocculant was purified to homogeneity by ethanol precipitation, DEAE ion-exchange and gel chromatography. Analysis of the purified polysaccharide showed that it consisted of glucose residues and had a molecular weight of 8.1 × 10⁴ Da. Its low molecular weight endowed it with excellent solubility and favorable flocculation activity, especially for small particulates.