Treatment of dairy process waters using a vibrating filtration system and NF and RO membranes

The permeate flux and chemical oxygen demand (COD) reduction were investigated in dairy process waters using a vibratory shear-enhanced filtration system (VSEP) and various nanofiltration (NF) and reverse osmosis (RO) membranes. Dairy process waters were simulated by UHT skim milk diluted 1:3 to obtain an initial COD of 36 000 mg O2 l−1. In NF the highest permeate flux (270 l h−1 m−2 at 4 MPa, 45 °C and initial concentration) was obtained with a Filmtec membrane which yielded also the highest permeate COD (94 mg O2 l−1). The best compromise was obtained with a Desal 5 DK membrane which yielded a COD of 36 mg O2 l−1 and a flux of 240 l h−1 m−2 under same conditions. In concentration tests, the permeate flux decreased with increasing volume reduction ratio (VRR) to reach 25 l h−1 m−2 for the 5 DK membrane at VRR=7 while permeate COD soared to 1050 mg O2 l−1.