Development of a novel submerged tubular direct-contact membrane distillation system for saltwater treatment

Membrane distillation (MD) is emerging as a promising alternative to current desalination systems because of its low energy consumption and investment cost. This study is aimed to develop a direct-contact membrane distillation (DCMD) system with a simple novel submerged tubular membrane module. The effect of feed temperatures (40°C, 50°C, 60°C and 70°C) on DCMD performance was investigated in the study. Additionally, pore wetting and surface scaling during the long-term operations were observed. As a result, the permeate flux is dependent on the feed tem-perature, with the flux increasing from 1.00 to 5.24 L/m² h as increased temperature from 40°C to 70°C. Such findings indicated the optimal feed temperature is at 60°C ± 0.5°C, being the permeate flux of 4.09 L/m² h under the cooling temperature of 28°C ± 1°C. Total dissolved solids, chlo-ride, and sulfate rejection efficiency were 99.36%, 99.91%, and greater than 98.74%, respectively. After 2 months of operation, pore wetting and surface scaling were detected through contact angle measurements and scanning electron microscopy and energy-dispersive X-ray spectroscopy. For flux enhancement, proper membrane materials and module arrangement should be further explored to develop a submerged tubular MD module for saline water treatment in developing countries.