Purification and characterization of compound bioflocculant

Two strains (designated F2, F6) which produce excellent flocculating substance were isolated from soil samples and identified as Rhizobium radiobacter and Bacillus sphaeicus. The compound bioflocculant (CBF) with higher flocculating activity was obtained by coculturing F2 and F6. The isolates F2 and F6 produced the flocculating substance during the late logarithmic growth phase and the early stationary growth phase, and the isolate F6 grew slower than isolate F2, so the time of producing CBF was prolonged. It was founded that the flocculation activated substances of CBF distributed mainly in upper phase and were mainly composed of polysaccharide (90.6%) and protein (9.3%). The CBF was thermo-stable and 75% of its activity remains after heating at 100°C for 30 min. With the pH value increasing from 7 to 9, the flocculation efficiency of CBF increased from 86% to 94%. The flocculation activated substances could be recovered from the supernatant of the fermented medium by cold acetone precipitation and purified by treating with Sevage reagent. After the preliminary extraction and purification, CBF remained high flocculating activity.