Sequential process: membrane filtration and ion exchange as an effective method for water solution purification containing cationic surfactants

Combination of the membrane process and ion exchange for the removal of cationic surfactants was investigated. Model solutions containing cetrimonium bromide (CTAB) and benzalkonium chloride (BAC) were treated. Polymeric nanofiltration and ultrafiltration modules were employed for the experiments. Ion-exchange tests were conducted in a batch mode with the use of two strongly acidic cation-exchange resins (C150H and Marathon 1200 Na). Tested solutions were characterized by a concentration range of surfactants below (50 mg/L), around (250 mg/L), and above (1,000 mg/L) the critical micelle concentration (CMC). In a sequential treatment, the permeate obtained over the membrane filtration cycle was directed to the ion exchange reactors. It was proved that the single purification process may not be sufficient in terms of both surfactant removal (in membrane pro- cesses due to the penetration of surfactant monomers into the permeate side) or economic aspects (in ion exchange due to a large amount of resin used). However, in the sequential purification system, both BAC and CTAB was removed with 100% efficiency from the solutions of initial concentrations below and around the CMC with the use of ultrafiltration and ion exchange. For highly concentrated BAC solutions, the best efficiency was seen when combining the ultrafiltration module and C150H resin (90% removal). In experiments with CTAB, for an initial surfactant concentration of 1,000 mg/L, the use of the ultrafiltration process, followed by ion exchange, allowed 99.6% of the surfactant to be removed.

Automated summary

The combination of membrane processes and ion exchange was investigated for the removal of cationic surfactants, with experiments showing that the sequential purification system achieved 100% efficiency in removing BAC and CTAB from solutions below and around the CMC. For highly concentrated solutions, a combination of ultrafiltration and C150H resin yielded a 90% removal efficiency for BAC, while a sequential process of ultrafiltration followed by ion exchange successfully removed 99.6% of CTAB from solutions with an initial concentration of 1,000 mg/L.