Membrane distillation of wastewater: comparison of model and real organics

Abstract

Fouling behaviour in membrane distillation (MD) processes plays a crucial role in determining their widespread acceptability. Most studies have primarily focused on model organic foulants, such as humic acid (HA) and sodium alginate (SA). This study investigates the fouling of a polytetrafluoroethylene membrane in a direct contact MD (DCMD) using model organics (i.e., HA and SA) and real wastewater. The results indicated that the flux decline (5–60%) was only observed during the initial phase of the operation with model organic foulants. In contrast, real wastewater caused a gradual decline in flux throughout the experiment in both the concentrate (40%) and continuous (90%) modes. The study also found significant differences in the fouling layer morphology, composition, and hydrophobicity between the model organic foulants and real wastewater. Fourier transform infrared spectroscopy findings demonstrated that the fouling layer formed by real wastewater varied significantly from model organics, which primarily comprised of protein-like and polysaccharide-like functional groups. Finally, liquid chromatography–organic carbon detection revealed that the fouling layer of the MD membrane with real wastewater was composed of 40.7% hydrophobic and 59.3% hydrophilic organics. This study suggests that model organics may not accurately reflect real wastewater fouling. HIGHLIGHTS Model organics and real wastewater exhibit different fouling behaviours in membrane distillation (MD).; Fouling layer by model organics was unevenly distributed and affected MD membrane properties.; Long-term (22 days) experiment showed continuous flux decline caused by organic–inorganic foulant interaction.; Real wastewater treatment instigated a membrane fouling layer consisting of proteins and polysaccharides.;

Keywords

• direct contact membrane distillation (dcmd)
• effluent organic matter
• humic acid
• organic fouling mechanisms
• sodium alginate