COMPARATIVE STUDY of DIFFERENT REVERSE OSMOSIS MEMBRANES FOR PROCESSING DAIRY FLUIDS: II. SPECIFIC SOLUTE EFFECTS?REJECTION COEFFICIENTS FOR TOTAL NITROGEN, NONPROTEIN NITROGEN, LACTOSE, COD, and ASH

Abstract

Solute rejection coefficients were measured for five different reverse osmosis membranes used to concentrate whole and skim milk and sweet and acid wheys. Rejection coefficients were determined for total nitrogen, nonprotein nitrogen, lactose, ash, and total chemical oxygen demand (COD). Cellulose acetate and thin film composite membranes were employed in both tubular and spiral wound configurations. the variations in the rejection coefficients with changes in process operating conditions (temperature, hydrostatic pressure/flow rate) were analyzed to assess the significance of the effects of these process parameters. All data were recorded under total recycle conditions so as to maintain a constant feed composition. For the four indicated feedstocks all membranes were capable of rejecting 100% of the protein at operating temperatures ranging from 70–120°F and at pressures of 3.1 and 4.5 MPa. Rejection coefficients for total nitrogen, non‐protein nitrogen, lactose, and total COD were affected by changes in process operating conditions, the type of feedstock, and the type of membrane employed. Rejection coefficients for ash were, in most cases, substantially insensitive to variations in operating pressure and temperature and to changes in the nature of the feedstock.