Single and multistage foam fractionation of rinse water with alkyl ethoxylate surfactants

The treatment of wastewater containing non-ionic alkyl ethoxylate. surfactants with foam fractionation was investigated in the laboratory. The influence of influent concentration, liquid height, foam height, and superficial air velocity on separation characteristics was determined in single-stage continuous operation. Changes in the parameters often had opposing effects on surfactant removal and enrichment. The degree of removal is most dependent upon the ratio of air flow to surfactant load, and the enrichment ratio is most dependent on effluent concentration and foam drainage time. Flotation performed in multistage units had higher removal degrees and lower enrichment ratios than that performed in single-stage units. Up to four columns were operated in series and compared. Through optimal foam heights and superficial air velocities for each stage, the removal degree and the enrichment ratio were improved and comparable with single-stage foam fractionation at equal mean residence times, surfactant concentration, and specific air flow rates. Under the chosen experimental conditions, three stages were optimal for separating surfactant from rinse water.