A bioflocculant TJ-F1 with high flocculating activity, produced by strain TJ-1 from a mixed activated sludge, was investigated with regard to its production and characterization. By 16S rDNA sequence and biochemical and physiological characteristics, strain TJ-1 was identified as Proteus mirabilis. The most preferred carbon source, nitrogen source and C/N ratio (w/w) for strain TJ-1 to produce the bioflocculant were found to be glucose, peptone and 10, respectively. TJ-F1 production could be greatly stimulated by cations Ca2+, Mg2+ and Fe3+. The optimal conditions for TJ-F1 production were inoculum size 2%o (v/v), initial pH 7.0, culture temperature 25 degrees C, and shaking speed 130 r/min, under which the flocculating activity of the bioflocculant reached 93.13%. About 1.33 g of the purified bioflocculant, whose molecular weight (MW) was 1.2 x 10(5) Da, could be recovered from 1.01 of fermentation broth. Chemical analysis of bioflocculant TJ-F1 indicated that it contained protein (30.9%, w/w) and acid polysaccharide (63.10/o, w/w), including neutral sugar, glucuronic acid and amino sugar as the principal constituents in the relative weight proportions of 8.2:5.3:1. Scanning electron microscopy (SEM) image of the purified solid-state Tj-F1 showed that it had a crystal-linear structure. Spectroscopic analysis of the bioflocculant by Fourier-transform infrared (FTIR) spectrometry indicated the presence of carboxyl, hydroxyl and amino groups preferred for the flocculation process. (c) 2007 Elsevier Ltd. All rights reserved.