Solar-driven membrane distillation and forward osmosis coupled system enables simultaneous water regeneration and metal recovery from wastewater

Abstract

With the in-depth implementation of green and low-carbon development principles, substantial progress has been achieved in water recycling and resource recovery technologies. However, the high energy consumption of current high salinity metal-laden wastewater treatment technologies continues to conflict with sustainable development goals, highlighting the need for innovative processes that leverage clean energy for wastewater regeneration and resource recovery. Here, we present a novel solar-driven membrane distillation and forward osmosis coupled system (SDOS), that integrates photothermal and photoelectric properties of solar to achieve both pure water regeneration and metal recovery from metal-laden wastewater, alongside electricity generation. SDOS consists of three core chambers: a feed solution chamber containing metal-laden wastewater, a draw solution chamber with Na₂-EDTA solution, and a permeate solution chamber filled with low-temperature deionized water. The titanium dioxide/graphitic carbon nitride (TiO₂/g-C₃N₄) photoanode is positioned within the draw solution chamber, while the carbon fiber cathode resides in the feed solution chamber. A forward osmosis (FO) membrane separates the feed and draw solution chambers, and a carbon nanotube-polyvinylidene fluoride (CNT-PVDF) membrane divides the draw and permeate solution chambers, establishing a fully integrated SDOS. Under solar irradiation, SDOS demonstrated a pure water regeneration rate of 0.81 L m⁻² h⁻¹ and a copper recovery rate of 5.9 mg h⁻¹ cm⁻², achieving a peak power output density of 820 mW m⁻². This study introduces the SDOS, a novel approach for the efficient and stable extraction of pure water from metal-laden wastewater using solar energy. The system achieves a salt rejection rate exceeding 99 % while concurrently enabling metal resources recovery and electricity generation. By integrating resource utilization with energy recovery, the SDOS provides a transformative solution for sustainable wastewater treatment.