Purification and regeneration of diluted caustic and acidic washing solutions by membrane filtration Original Research Article

The aim of the work was to purify diluted caustic and acidic streams from dairy cleaning-in-place processes (CIP). Nanofiltration of diluted dairy washing solutions, i.e. sodium hydroxide and nitric acid solutions, was studied with spiral wound modules. In addition, re-concentration of purified caustic and acidic washing solutions by reverse osmosis was studied. Nanofiltration reduced the COD content of the caustic washing solution by 76–90% depending on the concentration ratio used. The alkaline/acid content of the nanofiltration permeate was similar to the feed. By reverse osmosis treatment alkaline NF permeates were concentrated from 0.2 to 0.7% NaOH. Concentration of nitric acid did not succeed. The membranes retained their initial pure water fluxes when treated with the conventional CIP procedure after the filtration run.