Anionic and cationic surfactant recovery from water using a multistage foam fractionator

Surfactants can be present at low concentrations in effluent wastewater from various industrial operations. Also, the increasing use of surfactant-based separations results in surfactants in water generated by these separations. The surfactant concentration must sometimes be reduced in order to meet environmental standards in discharging these waters to the environment. Also, recovery of the surfactant for reuse is sometimes economical and desirable. Foam fractionation has been shown to be an effective method of removing anionic or cationic surfactants from water in a single stage in previous works. In this study, the recovery of a cationic surfactant (cetylpyridinium chloride, CPC) and an anionic surfactant (sodium dodecylsulfate, SDS) from water by multistage foam fractionation in a bubble-cap trayed column was investigated with one to four stages operated in steady-state mode for surfactant concentrations less than the critical micelle concentration (CMC). In a previous study of a single-stage foam fractionator, CPC was shown to be effectively removed from water, and in agreement with this study. In this study, multiple trays are investigated. Enrichment ratios as high as 120.23 were observed and increased with decreasing superficial air flow rate, increasing foam height of the top tray, increasing feed liquid flow rate, decreasing feed surfactant concentration, and increasing number of stages. The fractional surfactant removal can be as high as 100% and increases with decreasing air flow rate, increasing foam height per tray, increasing feed liquid flow rate, increasing feed surfactant concentration, and increasing number of stages. Scale-up of foam fractionation for recovery or removal of surfactant from water to a multi-tray column was successful. (C) 2003 Elsevier Science B.V. All rights reserved.