In processing full-fat soy flour to an acid-precipitated lipid protein concentrate a byproduct whey fraction results which, because of its high biological oxygen demand, represents a serious disposal problem. Processing of food waste streams by reverse osmosis has received considerable attention because of its low theoretical energy requirement since no phase change is involved. In a previous study at this Center a mathematical model was developed for the diffusive transport of soy lipid protein concentrate whey across cellulose acetate membranes. In this study, pumping energy and power costs combined with membrane life and replacement costs were incorporated into the original model to provide a basis for optimization from an energy cost standpoint. Computer-simulated runs were compared with experimental pilot-plant runs, and the agreement between predicted and actual results was quite good. Water flux rates were in the range of 3 to 7 gal/ft2/day. Computer runs were used to optimize the processing of 100,000 gal/day of soy whey at 8000 ppm biological oxygen demand (BOD). Costs were at a minimum with a six-stage tapered flow primary reverse osmosis treatment over a porous cellulose acetate membrane, followed by a six-stage tapered flow reverse osmosis over a tighter membrane. BOD reduction was 94% at a cost of $5.45/1000 gal.