High-yielding and stable desalination via photothermal membrane distillation with free-flow evaporation channel

Small-scale desalination devices driven by solar energy is a promising solution for freshwater in remote off-grid islands where centralized energy supplies are hardly accessible. However, the low water yield and unstable operation caused by energy inefficiency and salt precipitation are tricky problems. To provide a reliable freshwater supply, a desalination device with high water yield and no salt precipitation is the main target of this work. A three-stage photothermal membrane distillation module with free-flow evaporation channel was fabricated and a model was developed accordingly. Upon varying flow patterns and flow rates, the effects of different flow configurations on water production and salt concentration were observed and discussed. It is revealed that the feed from the bottom to the top stage in series connection at a flow rate of 28 ml h−1 can achieve a water production rate of 2.23 kg m−2 h−1 and a solar energy utilization efficiency as high as 147.9 % without salt precipitation. This work showed a competitive water production among all the previously reported small-scale solar membrane distillation devices. Besides, the flowing design is effective in preventing salt precipitation. A strong potential in providing qualified household freshwater with salinity rejection over 99 % on remote islands was indicated.