Iodide recovery and boron removal from thin-film transistor liquid crystal display wastewater through forward osmosis

For the first time, simultaneous iodide recovery and boron removal from thin-film transistor liquid crystal display wastewater were achieved using forward osmosis because iodide is a precious material and boron is toxic with 1 mg/L discharge standard in Taiwan. Cellulose triacetate and thin-film composite with aquaporin flat sheet membranes were tested for different feed solution, pH levels, and draw solution concentrations. The results indicated that the thin-film composite membrane had high boron and iodide rejections (98.4% and 98.3%, respectively) at a pH of 11; however, with a feed boron concentration of 600 mg/L, 9.8 mg/L boron was still present in the draw solution. Cationic surfactant cetyltrimethylammonium bromide was used to enhance the iodide recovery and boron removal efficiencies. Both efficiencies increased to 99.9% with 0.5 mM cetyltrimethylammonium bromide, and only 0.64 mg/L boron was present in the draw solution. In addition, negligible flux reduction was observed for forward osmosis process in the presence of cetyltrimethylammonium bromide. A membrane distillation system was used to concentrate and purify the MgCl₂ draw solution. Thus, the hybrid forward osmosis-membrane distillation process can be applied for iodide recovery and boron removal in the thin-film transistor liquid crystal display industry.