Fouling and wetting in the membrane distillation driven wastewater reclamation process – A review

Abstract

Fouling and wetting of membranes are significant concerns that can impede widespread application of the membrane distillation (MD) process during high-salinity wastewater reclamation. Fouling, caused by the accumulation of undesirable materials on the membrane surface and pores, causes a decrease in permeate flux. Whereas membrane wetting, the direct permeation of the feed solution through the membrane pores, results in reduced contaminant rejection and overall process failure. Lately, the application of MD for water recovery from various types of wastewaters has gained increased attention among researchers. In this review, we discuss fouling and wetting phenomena observed during the MD process, along with the effects of various mitigation strategies. In addition, we examine the interactions between contaminants and different types of MD membranes and the influence of different operating conditions on the occurrence of fouling and wetting. We also report on previously investigated feed pre-treatment options before MD, application of integrated MD processes, the performance of fabricated/modified MD membranes, and strategies for MD membrane maintenance during water reclamation. We also discussed energy consumption and economic aspects of MD for wastewater recovery. Throughout the review, we engage in discussions highlighting research needs for furthering the development of MD: notably the incorporation of MD in the overall wastewater treatment and recovery scheme (including selection of appropriate membrane material, suitable pre-treatment or integrated processes, and membrane maintenance strategies), and the application of MD in long-term pilot-scale studies using real wastewater.

An integrated fertilizer driven forward osmosis- renewables powered membrane distillation system for brackish water desalination: A combined experimental and theoretical approach

“…Both inorganic fouling and wetting are critical elements hindering the performance of the MD process for desalinating saline solutions [48]. In this work, the inorganic salt interacted either with each other or with the membrane surface creating salt deposits.…”

Powdered activated carbon (PAC) – vacuum-assisted air gap membrane distillation (V-AGMD) hybrid system to treat wastewater containing surfactants: Effect of operating conditions

“…After 5,000 min, the permeate conductivity began to increase, indicating that wetting started. Without SDS, wetting occurred due to membrane fouling due to salt precipitation [19]. Nevertheless, it was observed only after a long period.…”

“…While AGMD is applicable for the reclamation of high-salinity wastewater, it may suffer from critical problems caused by membrane wetting [19,20]. Membrane wetting is regarded as a primary barrier to the widespread industrial use of MD technology.…”

“…Membrane wetting is regarded as a primary barrier to the widespread industrial use of MD technology. Membrane wetting involves three stages: surface wetting, partial wetting, and fully wetting [19,20]. Surface wetting means that only the membrane surface is wetted by the liquid and does not affect membrane performance.…”

“…When the membrane pores are fully filled with liquid, the membrane becomes fully wet. A fully wetted membrane will lose its separation through MD [19].…”