Surfactant Recovery from Water Using a Multistage Foam Fractionator: Part I Effects of Air Flow Rate, Foam Height, Feed Flow Rate and Number of Stages

Abstract

Surfactants can be present at low concentrations in wastewater from many industries, such as papermaking or detergent manufacture. The surfactant must sometimes be reduced in concentration in order to meet environmental standards before discharging these wastewaters 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 and cationic surfactants from water in a single stage in our previous work. In this study, the recovery of a cationic surfactant (cetylpyridinium chloride or CPC) 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 or equal to the critical micelle concentration. In comparison with a single‐stage foam fractionator, CPC was found to be removed from water by the multistage foam fractionator much more effectively. Both enrichment ratio and surfactant removal fraction increase with increasing feed flow rate, foam height, and number of stages, but they decrease with increasing CPC feed concentration and air flow rate. This study has demonstrated that the multistage foam fractionator used in this study can achieve almost quantitative removal of the surfactant with high enrichment ratio and short residence time. Multistage foam fractionation is demonstrated to be an extremely effective method of reducing surfactant concentrations from low to even lower concentrations in wastewater.