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Foam separation of kraft mill effluents. Herchmiller, Donald Wayne

Abstract

A laboratory investigation into foam separation processes, as applied to kraft pulping and bleaching effluents is described. Two methods, foam fractionation and ion flotation were tested in the laboratory. The procedures developed concentrated primarily on the removal of effluent colour because this property lent itself most readily to the available analytical methods, and because effluent colour removal presents one of the greatest waste water treatment problems facing the industry today. The foam fractionation technique was not successful. Substantial colour removals were obtained, but it was subsequently shown that the mechanism of removal was really an ion flotation. Positive results were obtained with the use of the ion flotation process for removal of effluent colour. At optimum conditions, the recovery of flotable material and the corresponding removal of effluent colour were in excess of 95 per cent. Variation of surfactant dosage showed that below a critical level no colour was removed. As concentrations increased above this value the amount of colour removed increased rapidly, reaching a high removal level beyond which increases in surfactant concentration were of little value. The rate of flotation recovery was found to be significantly affected by the air sparge rate and the sparger pore size, both parameters which would determine the area available for adsorption. The pH of the flotation cell solution had a marked effect on the system. Optimum pH was clearly defined as 5.1. Removal of material other than just the chromophoric fraction was apparent. Biological oxygen demand data, while not extensive, demonstrate a significant reduction in the bio-degradable portion of the effluent. The possible future development of the process into a viable candidate for industrial application is discussed.

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