Separation of Microorganisms by Flotation

Separations of various microorganisms from water by flotation have been reported by Boyles and Lincoln (1958) and Gaudin (1957).In Part I of this paper (Gaudin, Mular, and O'Connor, 1960) quantitative assays for microbiological materials are described and results of application of these assay methods to flo- tation separations on menstrua of Bacillus subtilis var.niger are presented and discussed.In this paper, it is shown experimentally that sepa- rations can be made, and that the flotation behavior of spores and debris of B. subtilis var.niger is dependent upon the age of the bacterial components at harvest, the content of soluble liquid components in the flo- tation feed, the pH of the pulp, the prior heat treatment of the flotation feed (if any), and the addition of flo- tation reagents.EXPERIMENTAL METHODS Bacillus subtilis.var.niger spore preparations were either shipped direct from the U. S. Chemical Corps, Fort Detrick, Frederick, Maryland, or were grown at the Massachusetts Institute of Technology (M.I.T.) laboratories using Fort Detrick inoculum.Detailscon- cerning the spore preparations used in this work have been presented in Part I of this paper.Equipment Gaudin (1957) discussed the types of commercial flotation vessels which are available.In this work, flotation experiments were made with either a laboratory Fagergren flotation cell, a pneumatic flotation vessel of new design, or a small capacity sub- aeration device of modified design.Fagergren flotation cell.The description and operation of this cell is available in the book by Gaudin (1957).Results are reproducible, but the device is limited be- cause it is designed for pulps of low frothing tendelncy.Considerable quantities of spore sediment must be available if this cell is used since the vessel has a ca- pacity of 2.5 L.