Microfiltration characteristics of Bacillus subtilis fermentation broths

The microfiltration characteristics of Bacillus subtilis broths under different culture conditions were studied. In the no medium addition culture condition the major component in the broth was sole B. subtilis cells. The filtration curve of dt/dv vs. v (reciprocal of filtration flux vs. filtrate volume) can be divided into three regions. After a short relaxation time the tangent slope increases drastically. This implies that significant cell deformation and cake compression occurs in the second region. The average specific cake filtration resistance will reach the maximum value at the filtration curve inflection point. The cake compressibility gradually decreases in the third region because most solid compressive pressures are depleted by the formed compact cake. In the medium addition culture condition the B. subtilis cells and extracellular polymer substances (EPS) flocs concentrations in the broth increase markedly with culture time. The filtration curve tangent slope increases continuously during the entire filtration period because of the highly compressible cake. All proteins in the extra-cellular polymeric substances are retained by the filter cake and membrane during a filtration, while most polysaccharides have the opportunity to penetrate into the filtrate when the culture time exceeds 1 day. Polysaccharide rejection increases with increasing filtration pressure for the 1-day culture broth. However, the filtration pressure has a trivial effect on the polysaccharide rejection for longer culture times. The filter cake resistance formed by B. subtilis cells and EPS flocs plays an important role in determining the overall filtration resistance. A longer culture time and lower filtration pressure are beneficial for protein/polysaccharide separation using microfiltration.

► Culture and operating condition effects on filtration characteristics were studied.
► The filter cake resistance plays an important role on overall filtration resistance.
► All proteins are retained by the filter cake and membrane.
► The filtration pressure has a trivial effect on the polysaccharide rejection.
► Lower filtration pressure is beneficial for protein/polysaccharide separation.