Reclamation of sodium sulfate from industrial wastewater by using membrane distillation and membrane crystallization

Membrane distillation (MD) and membrane crystallization (MCr) have been applied for treatment of real industrial wastewater to produce high quality sodium sulfate. Simultaneously, MD and MCr minimize waste disposal and generate a fresh water stream. Untreated and wastewater pre-concentrated by nanofiltration have been utilized in MD and MCr under several operative conditions. The untreated wastewater indicated the steadiest performance. The MD and MCr operations have proven their long term stability throughout the concentration of wastewater. The treatment has been continued for more than 90 h for the untreated wastewater. Despite the utilized wastewaters have a high scaling potential in particular for silica, calcium and magnesium, no reduction in flux or wetting of the membrane surface have been observed due to fouling. Moreover, the crystalline product of Na2SO4 recovered as Thenardite (the anhydrous form) exhibits narrow size distribution and low incorporation of impurities.