Solar Seawater Distillation by Flexible and Fully Passive Multistage Membrane Distillation

Solar-assisted distillation is considered promising to solve the freshwater supply for off-grid communities. In this work, a passive and flexible multistage membrane distillation (F-MSMD) device is devised to produce freshwater via solar distillation with the latent heat of vapor condensation being recycled to enhance its energy efficiency. By designing a siphon effect, source water is continuously wicked into the evaporation layer and the concentrated brine flows out of the device before reaching saturation, which successfully solves the otherwise challenge of salt accumulation inside the device. To achieve such siphon flow, the recycled paper is prepared from spent copy paper and used as the evaporation layer for efficient water delivery owing to its large pore size and high hydrophilicity. An eight-stage F-MSMD device exhibits a stable clean water production rate at 3.61 kg m^-2 h^-1 in the newly designed siphon-flow mode. This work provides a green route for designing a solar-assisted distillation device.