The present invention generally relates to the field of water treatment, and in particular to polymer inclusion membranes for use in industrial processes which generate aqueous solutions containing thiocyanate (SCN). The invention particularly relates to polymer inclusion membranes for use in processes for treating aqueous solutions containing SCN and more specifically polymer inclusion membranes comprising (i) about 10-20% wt/wt of a quaternary ammonium salt of formula (I) wherein R1 -R4 are independently alkyl chains and X⊖ is an anion; (ii) about 5-30% wt/wt of a plasticizer/ modifier; and (iii) about 50% wt/wt of a polymer selected from the group consisting of poly(vinyl chloride), cellulose triacetate, and derivatives thereof.