Nota Científica: ultrafiltração de efluente da indústria de laticínios para recuperação de nutrientes: efeito da pressão e da velocidade tangencial

The cleaning process used in the dairy industry generates a great volume of effluent, engendering up to 10 L of effluent per litre of milk processed. The first rinsing water can carry off 1%-3% of the milk solids, representing production costs. Ultrafiltration can be used to recover these milk solids aiming to reinsert them into the process. The goal of this work was test two ultrafiltration membranes with different configurations (tubular and spiral) with different pressures and cross-flow velocities to recover and concentrate these milk solids, aiming to obtain a dairy compound capable of reuse. The process was evaluated and optimized using a model rinsing water (1.7 g.L-1 of whole milk powder diluted in tap water), fed to a cross-flow ultrafiltration equipment, varying the pressure (98; 196 and 194 kPa for both membranes) and cross-flow velocities (0.79; 1.42; 2.23 m.s-1 for the tubular membrane and 0.15; 0.27; 0.44 m.s-1 for the spiral membrane), using a 32 factorial design. The dependent variables were the permeate flow rate, the Chemical Oxygen Demand (COD), and the protein, fats and oils, lactose, phosphorus and calcium concentrations in the permeate. The optimized test conditions for the tubular membrane were obtained with a pressure of 294 kPa (raising the lactose rejection  -  562 mg.L-1 of this compound in the permeate) and a cross-flow velocity of 2.23 m.s-1 (increasing the permeate flow rate  -  93.2 kg.m - 2.h-1 and reducing the fats and oils concentration in the permeate to 39 mg.L-1). With the spiral membrane, the pressure and cross-flow velocity only affected the permeate flow rate (reaching 34.8 kg.m - 2.h-1) with no significant effect on the other dependent variables. The process carried out with this membrane was optimized with a pressure of 294 kPa and 0.44 m.s-1. The rejection of both membranes was higher than 70% for COD, 94% for protein and above 85% for fat. The model rinsing water was concentrated with the spiral membrane, reducing the initial volume 34 times. The dairy concentrate obtained had 2.3% total solids, 1.1% protein and 0.9% fat. Ultrafiltration was shown to be a possible process to recover milk solids in the dairy industry.

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