Studies on polymeric nanofiltration-based water softening and the effect of anion properties on the softening process

The water softening capability of a polymeric NF-based membrane is investigated in a cross-flow mode. Also, the effects of the anion properties binding to the cation in the feed water are investigated. The softening process is monitored using parameters such as apparent rejection, softening factor, relative softened water recovery and the relative softened water purity to assess the effects of the operating conditions on the softening process. Moreover, a combined solution–diffusion/film theory (SDFT) model reduced to Gupta’s model (dilute solutions) is employed to extract three (3) parameters: the hydraulic permeability (Lp), the reflection coefficients (σ) and the solute permeability (ω) which characterizes the membrane. Preliminary, results show the membrane to possess good water softening properties while the charge, size, and the shape of the anions each play a vital role in the water softening process. Thus, the above protocol provides techniques for monitoring, characterizing and selecting potential polymeric membranes for water softening applications.