WAN Ying-xin, XU Jing, YANG Xue-jing, LI Rui,

(The College of Arts and Sciences of Beijing Union University, Beijing 100083, China)

Abstract:  A fungus strain(J-5) which can produce bioflocculant was isolated from activated sludge. It was identified as Geotrichum candidum in terms of its morphological and physiological characteristics, the partial sequences of its 18S rDNA and the contents of G+C. The growth of the isolated Geotrichum candidum was maximal after 3 days of cultivation while the highest flocculating activity of the culture broth was observed after 1 day of cultivation. The test results of bioflocculant activity for Geotrichum candidum showed that the active ingredient of bioflocculant existed in the free-cell supernatant. The crude bioflocculant could be recovered from the supernatant of the culture broth by ethanol precipitation and dialysis against deionized water. The polymer was identified to be a polysaccharide containing neutral sugar and uronic acid as its major and minor components, respectively. Infrared spectra showed the presence of hydroxyl, carboxyl and methoxyl groups in its molecules.

Key words: Geotrichum candidum; bioflocculant; flocculating characteristics