Treatment of complex multi-sourced industrial wastewater — New opportunities for nanofiltration membranes

Restrictions on the volume of organics discharged from industrial wastewater (IWW) treatment plants has created an impetus to implement nanofiltration (NF) membrane technology at these facilities. However, NF membranes are rated based on simple performance metrics (i.e. permeability and salt rejection), not their capacity to reject organic content. In this study, three IWW samples with varying concentrations (measured via COD) and compositions (analyzed via gas chromatography-mass spectrometry) were filtered using four commercial NF membranes (NF90, TS80, NFS and NFX). The NF90 membrane demonstrated the best COD removal, however compositional differences between samples significantly influenced the magnitude of COD reduction, the permeate flux performance during filtration, and the change in the measured hydraulic permeability and salt rejection after wastewater filtration. To investigate this further, separate solutions of commonly occurring chemical compounds (benzyl alcohol, 2-phenyl ethanol, pentanoic acid) were made with equivalent COD concentrations and filtered using the NF90 and NFX membranes. The NF90 membrane demonstrated significantly better COD removal for all three solutions. It was found that the NFX membrane achieved an increase in permeate flux during constant pressure filtration which was attributed to a “solvent activation” phenomena. These results serve as “proof-of-concept” that commercial NF membranes can significantly reduce the COD concentration of IWW, however, performance metrics that encompass both bulk and compositional properties must be adopted and standardized.