Membrane Distillation Hybrid Peroxydisulfate Activation toward Mitigating the Membrane Wetting by Sodium Dodecyl Sulfate.

Minyuan Han,Lang Liu,Xiaobo Li,Daoling He,Ruixue Zhao,Jianchao Shi,Le Han

doi:10.3390/membranes12020164

Abstract

The fouling/wetting of hydrophobic membrane caused by organic substances with low-surface energy substantially limits the development of the membrane distillation (MD) process. The sulfate radical ()-based advanced oxidation process (AOP) has been a promising technology to degrade organics in wastewater treatment, and peroxydisulfate (PDS) could be efficiently activated by heat. Thus, a hybrid process of MD-AOP via PDS activated by a hot feed was hypothesized to mitigate membrane fouling/wetting. Experiments dealing with sodium dodecyl sulfate (SDS) containing a salty solution via two commercial membranes (PVDF and PTFE) were performed, and varying membrane wetting extents in the coupling process were discussed at different PDS concentrations and feed temperatures. Our results demonstrated permeate flux decline and a rise in conductivity due to membrane wetting by SDS, which was efficiently alleviated in the hybrid process rather than the standalone MD process. Moreover, such a mitigation was enhanced by a higher PDS concentration up to 5 mM and higher feed temperature. In addition, qualitative characterization on membrane coupons wetted by SDS was successfully performed using electrochemical impedance spectroscopy (EIS). The EIS results implied both types of hydrophobic membranes were protected from losing their hydrophobicity in the presence of PDS activation, agreeing with our initial hypothesis. This work could provide insight into future fouling/wetting control strategies for hydrophobic membranes and facilitate the development of an MD process.

Highlights

Membrane distillation (MD) is a thermal desalination process that uses microporous hydrophobic membrane to separate the hot, salty feed and cold distillate
The in-air contact angles (CAs) of the PVDF and PTFE membranes were quite comparable (115 ± 2° and 120 ± 3°, respectively), and the CA value of each membrane slightly decreased with lower surface energy liquids (50 and 45 mN/m for 0.5 mM and 0.8 mM sodium dodecyl sulfate (SDS), respectively, in respect with ca. 72 mN/m for DI water) (Figure A1)
The results indicated that the featured peak for SDS was only slightly observable on the PTFE membrane dealing with feed containing a relatively higher SDS quantity

Summary

Introduction

Membrane distillation (MD) is a thermal desalination process that uses microporous hydrophobic membrane to separate the hot, salty feed and cold distillate. Membrane-based desalination technologies (e.g., reverse osmosis), the advantages of MD include the utilization of recyclable heat or solar energy, low sensitivity to feed salinity, affordable operating conditions such as low pressure and moderate temperature [4]. Surfactants are widely used in household goods, detergents, and many other aspects in modern industrial activities [8]. They could readily adhere to the membrane surfaces in MD via hydrophobic and/or electrostatic interactions, gradually sacrificing the pore hydrophobicity during the propagation of the liquid–air interface under the liquid entry scenario [9,10,11]. Despite the development of bespoke MD membranes with special wettability being imperative to overcome these issues, solution polishing to reduce its wetting propensity via adequate pretreatments is a reasonable strategy [12,13]

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