Foam Separation of Pseudomonas fluorescens and Bacillus subtilis var. niger

ABSTRACT

An experimental investigation established the effect of the presence of inorganic salts on the foam separation of Pseudomonas fluorescens and of Bacillus subtilis var. niger (B. globigii) from aqueous suspension by use of a cationic surfactant. For P. fluorescens, 5.0 μeq/ml of NaCl, KCl, Na₂SO₄, K₂SO₄, CaCl₂, CaSO₄, MgCl₂, or MgSO₄ produced increases in the cell concentration in the residual suspension (not carried into the foam) from 2.9 × 10⁵ up to 1.6 × 10⁶ to 2.8 × 10⁷ cells per milliliter (initial suspensions contain from 3.3 × 10⁷ to 4.8 × 10⁷ cells per milliliter). The exceptional influence of magnesium was overcome by bringing the cells into contact first with the surfactant and then the salt. For B. subtilis, the presence of 5.0 μeq/ml of any of the eight salts increased the residual cell concentration by one order of magnitude from 1.2 × 10⁴ to about 4.0 × 10⁵ cells per milliliter. This occurred regardless of the sequence of contact as long as the surfactant contact period was sufficient. The presence of salts increased collapsed foam volumes with P. fluorescens and decreased collapsed foam volumes with B. subtilis.