Sustainable FO-UVA/electrobromine-MD system for high-purity water production from secondary effluent

The fast growth of cutting-edge industries (e.g., semiconductor and energy storage) intensifies the demand for high-purity water, posing a potential threat to public needs for freshwater resources. The hybrid forward osmosis (FO)-membrane distillation (MD) process has been demonstrated to produce high-purity water from non-traditional water sources (e.g., wastewater). However, the FO-MD process suffers from the contaminant accumulation in the draw solution, which might affect the product water quality and result in membrane fouling and wetting during long-term operation. To mitigate the contaminant accumulation in the draw solution, this study proposed to combine the FO-MD process with the UVA/electrobromine process as an FO-UVA/electrobromine-MD system. In the system, bromine was generated in situ by the electrooxidation of bromide in the draw solution and exposed to the UVA irradiation to produce reactive species for contaminant degradation. The hybrid membrane system, with or without the UVA/electrobromine treatment, produced high-purity water (conductivity < 2.0 μS cm–1) from synthetic secondary effluent and removed five selected contaminants by more than 99.99%. With the dosage of the selected contaminants at 1000 nM for each in the feed solution (i.e., synthetic secondary effluent), the contaminant concentrations accumulated to 27–877 nM in the draw solution of the FO-MD system without in situ treatment at the water recovery rate of 60%. In the FO-UVA/electrobromine-MD system, the in situ oxidation treatment removed the accumulated contaminants by more than 99.9%, attributed to the generated non-radical species (e.g., Br2O and Br3–), Br2O–, and BrO●. The investigation into the removal of effluent organic matter constituents (e.g., proteins, carbohydrates, and humic substances) by the system is on-going and will also be discussed in the presentation.