Modeling of lactic acid rejection from lactose in acidified cheese whey by nanofiltration

The continuously increasing demand of lactic acid opens a window for the integration of membrane technology in the dairy industry, improving the sustainability by avoiding the use of large amounts of chemicals and waste generation. Lactic acid recovery from fermentation broth without precipitation has been studied by numerous processes. In this work, a commercial membrane with high lactose rejection and a moderate lactic acid rejection, enabling a permselectivity up to 40%, is sought to perform the simultaneous removal of lactic acid and lactose separation from the acidified sweet whey from mozzarella cheese production in a single stage. The AFC30 membrane of the thin film composite nanofiltration (NF) type was selected because of its high negative charge, low isoelectric point, and divalent ion rejection, as well as a lactose rejection higher than 98% and a lactic acid rejection lower than 37%, at pH 3.5, to minimize the need of additional separation steps. The experimental lactic acid rejection was evaluated at varying feed concentration, pressure, temperature, and flow rate. As the dissociation degree of lactic acid is negligible in industrially simulated conditions, the performance of this NF membrane was validated by the irreversible thermodynamic Kedem-Katchalsky and Spiegler-Kedem models, with the best prediction in the latter case, with the parameter values: L_p = 3.24 ± 0.87 L × m⁻² × h⁻¹ × bar⁻¹ and = 15.06 ± 3.17 L × m⁻² × h⁻¹, and σ = 0.45 ± 0.03. The results obtained in this work open the way for the up-scaling of membrane technology on the valorization of dairy effluents by simplifying the operation process and the model prediction and the choice of the membrane.     

Stationary states of hydrogen-producing reactions in nonequilibrium plasma

In this work, stationary states of hydrogen-producing reactions in nonequilibrium plasmas are explored, namely the water splitting and water gas shift reactions. For both reactions, the effluent from the reactor at long residence times in the plasma was found to be independent of the influent speciation. In other words, feeding the reactor either 0.1H₂O or 0.1H₂ + 0.05O₂ by mole produced the same effluent composition, and similarly, feeding the reactor 0.1CO + 0.1H₂O produced nominally the same effluent as 0.1CO₂ + 0.1H₂. For both reactions, the effluent from the plasma was found to be very far from local equilibrium at the total pressure and background temperature of the plasma and shifted in the endothermic direction relative to the local equilibrium speciation. This work further demonstrates that special attention must be paid to the recombination zone in plasmachemical processes. The recombination zone tends to drive the gas composition from plasma stationary states back towards local equilibrium.