Technological advancements in water heating approaches for membrane distillation desalination process: From bulk to localized heating

Feedwater heating represents a pivotal and energy-intensive step in membrane distillation (MD), contributing significantly to the total energy costs. Thus, elevating the thermal efficiency of the MD process is vital for its broader energy optimization. Recent years have witnessed an uptick in research targeting the enhancement of thermal efficiency in MD systems, particularly in the realm of innovative feedwater heating techniques. This comprehensive review delivers an in-depth examination of diverse feedwater heating methods utilized in MD, spanning both bulk and localized heating approaches. Bulk heating methods involve the utilization of solar panels, solar collectors, solar ponds, waste heat, and geothermal energy to heat bulk feedwater. Conversely, localized heating techniques include photothermal heating via direct solar light, joule heating, microwave-assisted heating, and induction heating. This review delves into the techno-economic viability of transitioning from bulk to localized heating in MD and provides a qualitative assessment of the inherent challenges each technology presents. Ultimately, this review is an invaluable reference for the research community, shedding light on recent advancements, developmental phases, operational methodologies, obstacles, and opportunities specific to each water heating technique within MD's framework.