Pressure-driven membrane and ion exchange hybrid system for the treatment of wastewater containing sulfite and nitrite

Abstract

Denitrification of flue gas can generate a large amount of wastewater. Depending on the denitrification technology used, the water could contain a fair amount of sulfite and nitrite that need to be removed for water reuse or discharge. An integrated pressure-driven membrane and ion exchange (IX) process is therefore designed and tested for this purpose in this work. The process contains a combination of nanofiltration (NF), reverse osmosis (RO), and a mixed bed IX. NF was performed on a DL1812 membrane module at 2.0 MPa using a simulated wastewater containing 63.0 g/L Na2SO3 and 49.5 g/L NaNO2. Sulfite was separated from nitrite with a retention rate of 92.0%, and its overall recovery efficiency achieved 91.09%. The recovery rate of nitrite in the permeate of NF was 71.06%, which was further elevated by RO using a SG1812 membrane module. A four-pass RO process was shown to be capable of recovering 98.15% of NaNO2 in the final retention. Finally, it was demonstrated that followed by IX treatment, sulfite and nitrite were successfully removed to meet the water surface discharge criteria, proving the feasibility of the hybrid NF–RO–IX system as a viable alternative for treating and reusing denitrification wastewater.