Prevention of surfactant wetting with agarose hydrogel layer for direct contact membrane distillation used in dyeing wastewater treatment

• An agarose hydrogel layer was attached to PTFE membrane for MD process.
• Surfactant wetting was prevented during MD withagarose-covered PTFE membrane.
• When surfactant was above its CMC, agarose layer cannot prevent membrane wetting.
• MD with agarose-covered PTFE membrane caused no wetting on treating wastewater.
• The anti-wettability may be due to the entrapment of surfactant by the hydrogel.

A novel approach was developed to suppress surfactant wetting during membrane distillation process for industrial wastewater treatment. In this work, a thin layer of agarose hydrogel was attached to the surface of hydrophobic porous Teflon membrane. This composite membrane was tested against aqueous NaCl solution containing various surfactants to determine the effectiveness for preventing surfactant wetting. These surfactants included sodium dodecyl sulfonate (SDS), Tween20, and Tween85. The results showed that no wetting occurred during the 24 h period of membrane distillation against 10 mg/L of SDS or Tween20. On the other hand, surfactant still penetrated through the hydrogel when the concentration was above the critical micelle concentration (CMC) of the surfactant. Even so, the wetting occurred to a lower extent at a slower pace. In addition, no wetting was observed when testing against dyeing wastewater. A model to explain this phenomenon was proposed based on the entrapment of surfactant at the interface between water and hydrogel. Although the attachment of agarose hydrogel layer would reduce the flux to about 71% of the flux using bare membrane, this approach did make membrane distillation able to recover high purity water from dyeing wastewater.

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