A fluid treatment arrangement comprising: first and second end pieces (11, 12); a first fluid treatment unit and a second fluid treatment unit positioned between the end pieces (11, 12), said first and second fluid treatment units having a multilayer structure which includes a feed layer, a permeate layer, and a layer of a permeable fluid treatment medium positioned between the feed layer and the permeate layer, wherein the permeable medium has a feed side fluidly communicating with the feed layer and a permeate side fluidly communicating with the permeate layer, the fluid treatment units further including first and second opposite end surfaces (22, 23) and a thermoset which holds the layers (14, 15, 16) of the multilayer structure together and which forms at least a first portion of the first end surface, and first and second impermeable thermoplastic sheets positioned between the first end surfaces of the first and second fluid treatment units, each impermeable thermoplastic sheet having first and second opposite surfaces, the thermoset on the first end surface of the first fluid treatment unit directly bonding to the first surface of the first impermeable thermoplastic sheet, the thermoset on the first end surface of the second fluid treatment unit directly bonding to the first surface of the second impermeable thermoplastic sheet, wherein the first surface of the first thermoplastic sheet and the first surface of the second thermoplastic sheet are textured so as to provide an enlarged surface area to which the thermoset is bonded and are modified to alter the surface energy and enhance the bond between the thermoset and the first surface of the first thermoplastic sheet and the bond between the thermoset and the first surface of the second thermoplastic sheet, and wherein the second surfaces of the first and second thermoplastic sheets are bonded to one another. first and second end pieces (11, 12); a first fluid treatment unit and a second fluid treatment unit positioned between the end pieces (11, 12), said first and second fluid treatment units having a multilayer structure which includes a feed layer, a permeate layer, and a layer of a permeable fluid treatment medium positioned between the feed layer and the permeate layer, wherein the permeable medium has a feed side fluidly communicating with the feed layer and a permeate side fluidly communicating with the permeate layer, the fluid treatment units further including first and second opposite end surfaces (22, 23) and a thermoset which holds the layers (14, 15, 16) of the multilayer structure together and which forms at least a first portion of the first end surface, and first and second impermeable thermoplastic sheets positioned between the first end surfaces of the first and second fluid treatment units, each impermeable thermoplastic sheet having first and second opposite surfaces, the thermoset on the first end surface of the first fluid treatment unit directly bonding to the first surface of the first impermeable thermoplastic sheet, the thermoset on the first end surface of the second fluid treatment unit directly bonding to the first surface of the second impermeable thermoplastic sheet, wherein the first surface of the first thermoplastic sheet and the first surface of the second thermoplastic sheet are textured so as to provide an enlarged surface area to which the thermoset is bonded and are modified to alter the surface energy and enhance the bond between the thermoset and the first surface of the first thermoplastic sheet and the bond between the thermoset and the first surface of the second thermoplastic sheet, and wherein the second surfaces of the first and second thermoplastic sheets are bonded to one another.