Feasibility of forward osmosis using ultra low pressure RO membrane and Glauber salt as draw solute for wastewater treatment

Abstract

Glauber salt (sodium sulfate decahydrate, Na2SO4·10H2O) is presented as a viable draw solute in forward osmosis (FO) process for dewatering of textile wastewater and brackish water. A widely available, commercial, low cost ultra low pressure reverse osmosis membrane is used in a bench scale FO unit. Water flux of 7 L m−2 h−1, 4.3 L m−2 h−1 and 5.3 L m−2 h−1 were obtained with DI water, synthetic wastewater and industrial wastewater feed solution using 1.5 M Na2SO4 draw solution. Desalination of brackish water (0.25 NaCl) and sea water (0.6 M NaCl) yielded water flux of 4.5 L m−2 h−1 and 2.6 L m−2 h−1 respectively. A minimal reverse salt flux of 0.42 g m−2 h−1 was attained with 1 M Na2SO4 draw solution against DI feed water. The diffusion coefficient for the FO process was determined to be 0.8 × 10-9 m2 s−1 and the membrane solute resistivity value was 1.25 × 107 s m−1. Reversible fouling caused by scattered and non-uniform loose deposition of particles at the membrane surface was observed which was easily cleaned and 90% water flux could be restored. Recovery of draw solute was attempted by low pressure nanofiltration process using less energy. Good quality permeate containing negligible salt (<150 mg L−1 TDS) was generated at <5 atm. pressure. An alternative utilization of dilute Glauber salt solution for production of dilute fertilizer solution eliminating recovery process is proposed. Overall, the versatility and feasibility of the FO process with locally availableresources giving good performance has been established.