Production and characterization of a thermostable bioflocculant from Bacillus subtilis F9, isolated from wastewater sludge

• Low molecular weight bioflocculant was produced by B. subtilis F9.
• The bioflocculant was pH- and thermostable.
• Maximum bioflocculant production was 2.32 g L−1.
• The bioflocculant has potential applications in drinking water treatment.

A bacterium isolated from wastewater sludge, identified as Bacillus subtilis F9, was confirmed to produce bioflocculant with excellent flocculation activity. The effects of culture conditions such as initial pH, temperature, carbon source, nitrogen source, and inoculum size on bioflocculant production were studied here. The results indicated that 2.32 g/L of purified bioflocculant could be extracted with the following optimized conditions: 20 g L−1 sucrose as the carbon source, 3.5 g L−1 peptone as the nitrogen source, an initial pH of 7.0, and a temperature of 40 °C. The purified bioflocculant consisted of 10.1% protein and 88.3% sugar, including 38.4% neutral sugar, 2.86% uronic acid, and 2.1% amino sugar. The neutral sugar consisted of sucrose, glucose, lactose, galactose, and mannose at a molar ratio of 2.7:4.7:3.2:9.1:0.8. Elemental analysis of the purified bioflocculant revealed that the weight fractions of carbon, hydrogen, oxygen, nitrogen, and sulfur were 30.8%, 5.3%, 54.7%, 6.4%, and 2.9%, respectively. Furthermore, the purified bioflocculant was pH tolerant within the range of 2–8 and thermotolerant from 10 °C to 100 °C, with optimal activity at pH 7.0 and at a temperature of 40 °C. The purified bioflocculant showed industrial potential for the treatment of drinking water. Considering these properties, especially its low molecular weight (5.3×104 Da), this bioflocculant with excellent solubility and favorable flocculation activity is particularly suited for flocculating small particles.