Multi-pass shell and tube concentric tubular module design for membrane distillation for desalination and wastewater treatment

Graphical abstract illustrating a novel multi-pass concentric membrane distillation module designed for treating saline water and wastewater. The illustration shows the three-dimensional module assembly, exploded view of its components, and schematic representation of the concentric flow channels, including feed circulation through the inner and outer shells and vapor/permeate collection. The proposed configuration enables feed recirculation and efficient membrane utilization, offering a compact, energy-efficient, versatile design with improved permeate flux for water purification and desalination applications. Although membrane distillation (MD) is widely applied in desalination and wastewater treatment, its industrial-scale implementation remains limited due to low permeation flux caused by inefficient membrane module design. This necessitates the development of better designs for MD modules that address the drawbacks of traditional MD module designs, including limited flexibility, low compactness, design complexity, and performance limitations. In this study, a multi-pass concentric tubular module for the MD process is presented for desalination and wastewater treatment. The developed module offers a simple design with enhanced efficiency, flexibility, and compactness, enabling integration of vacuum MD and direct-contact MD functionalities within a single unit. The module uses flat-sheet membranes, resulting in high packing density, scalability, and energy efficiency. Further, the module incorporates a multi-pass feed recirculation technique and low-conductivity construction materials, resulting in improved heat and mass transfer efficiency. The module is also capable of treating two different feed streams simultaneously using a multi-feed configuration with a single permeate stream. Moreover, different membranes can be mounted on the inner and middle shells based on feed quality and requirements. The application of the module has been demonstrated by treating saline water, textile, and pharmaceutical wastewater to establish the robustness of the proposed design. The developed module demonstrated stable performance, achieving permeate fluxes of 5.63 L m−2 h−1 in vacuum MD mode and 4.95 L m−2 h−1 in direct-contact MD mode, with high salt rejection (>99%).