Economics of Reverse Osmosis and Multistage Evaporation for Concentrating Skim Milk from 8.8 to 45% Solids

Reverse osmosis used in the concentration range of 8.8 to 25% by weight of solids reduces the cost of concentrating skim milk in comparison of multistage evaporation. Membranes used for skim milk limit the maximum practical concentration to approximately 25%. When reverse osmosis and multistage evaporation are used in combination to concentrate skim milk from 8.8 to 45% solids, with a reverse osmosis final concentration of 25%, capital and operating costs are equivalent to those for multistage evaporation from 8.8 to 45%. However, energy requirements for the combination of reverse osmosis and evaporation are much lower than for multistage evaporation alone, a minimum of 75,800 kJ/Mg of water removed (reverse osmosis 8.8 to 25%; multistage evaporation 25 to 45%) versus 277,000 for evaporation. This study presents preliminary approximation of costs and economics for reverse osmosis and a preliminary economic comparison of reverse osmosis, evaporation, and the combination of reverse osmosis and evaporation. The concentration range of 8.8 to 45% solids is typical for feed preparation of skim milk before spray drying to powdered skim milk.