Treatment of dairy process waters by membrane operations for water reuse and milk constituents concentration

In the dairy industry non-accidental losses of milk or dairy products to sewer amount to 1-3% of the total milk processed. These significantly contribute to the 0.5-6.0 g COD/L of end-of-pipe waste-water. The major part of this polluting charge originates from starting, interrupting, and stopping dairy plant procedures, where milk-products are diluted with water and discharged to a purification station or collected to be spread on land. The very few works, that have been dedicated to the treatment of the so-called process waters (flushing waters, first rinse waters or "white waters"), show that nanofiltration (NF) or reverse osmosis (RO) is adequate for the concentration of milk components. The present work reports NF and RO performances (permeate flux, milk components rejection) of an effluent model solution (diluted skimmed milk). Performances of eight NF and RO membranes were compared by dead-end filtration. Crossflow experiments with NF and RO spiral-wound membranes confirm the results obtained by dead-end filtration. The results showed that one single membrane operation allowed the milk constituents to be concentrated in the retentate but reusable water of composition complying with the standard of purified water from process water was not reached. A finishing step (RO membrane, other) is needed for the production of reusable water.