Abstract
Acid whey is a by-product of cheese and yoghurt manufacture. The protein and lactose within acid whey can be recovered using nanofiltration and electrodialysis, but this leaves a waste stream that is a mixture of salts and lactic acid. To further add value to the acid whey treatment process, the possibility of recovering this lactic acid was investigated using either low energy reverse osmosis membranes or an electrodialysis process. Partial separation between lactic acid and potassium chloride was achieved at low applied pressures and feed pH in the reverse osmosis process, as a greater permeation of potassium chloride was observed under these conditions. Furthermore, lactic acid retention was enhanced by operating at lower temperature. Partial separation between lactic acid and potassium chloride was also achieved in the electrodialysis process. However, the observed losses in lactic acid increased with the addition of sodium chloride to the feed solution. This indicates that the separation becomes more challenging as the complexity of the feed solution increases. Neither process was able to achieve sufficient separation to avoid the use of further purification processes.
Highlights
Using Membrane Technology.Lactic acid is a valuable organic acid used in the food, pharmaceutical, leather, textile, and chemical industries
The limiting current density of the ED membranes was measured for a solution of g/L KCl and 1 g/L of lactic acid, using a six compartment electrodialysis cell
The waste streams generated from acid whey treatment are a valuable source of lactic acid
Summary
Many researchers have examined the use of different membrane technologies, such as nanofiltration (NF), dia-nanofiltration (Dia-NF) and electrodialysis (ED), to remove 30–80% of the lactic acid originally present [4,7,8] These processes leave a waste stream that represents an unutilized source of lactic acid. To separate lactic acid from a salt solution, several researchers have investigated the use of pressure driven membrane technology, such as NF. Several other factors affect the lactic acid permeation through NF, namely feed solution pH, process temperature, membrane material, the concentration of lactic acid in the feed, and mineral solubility [17]. Membranes 2021, 11, 107 within the ED diluate was evaluated by the addition of sodium chloride (NaCl) to the feed stream
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