High-density filtration module

A method for economically recovering pigment from electrocoat painting wastewater feed, which method comprises the steps of:

• (a) feeding said wastewater axially through a high-density membrane module, which module comprises:
• a plurality of sheets of porous membrane having pores sized to allow passage of liquid in a transverse direction while rejecting passage therethrough of solid pigments and the like in said feed, said sheets of membranes being arranged in essentially coaxial cylinders about a central axis,
• flexible feed spacer sheet material disposed adjacent the active entry surface of each said membrane sheet, said spacer material comprising a thin central layer and two sets of individual ribs, each set projecting from an opposite surface of said central layer and each including a plurality of parallel ribs of similar size regularly spaced apart from one another with tips of said ribs contacting said membrane sheets so as to maintain spacing therebetween to form uniform feed-carrying channels, the regions between said parallel ribs being completely open and oriented so that said channels extend in a generally axial direction of flow,
• said ribs providing between 2 and about 10 channels per inch and being generally triangular in cross-section with said tips being smoothly rounded,
• said central layer having a thickness “t” about 40% or less than the thickness “e” of said ribs at their bases, and
• a permeate carrier layer disposed adjacent a discharge surface of each said membrane sheet, said permeate carrier conducting the discharge flow of water from said module, and
• (b) withdrawing liquid from said module for extended periods of time at a permeate flux of at least about 10 Lmh and, at an inlet pressure of 100 psig or less, when being used to reclaim pigment from electrocoat painting wastewater.