• 한국생물공학회:학술대회논문집
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• 2000.04a
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• pp.489-492
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• 2000

The rejection of hardness in a lactate fermentation broth was investigated by NTR-729 nanofiltration membrane. Firstly, a method for determining membrane surface charge was proposed on the basis of the rejection data for NaCl, $Na_2SO_4$, $MgCl_2$, $MgSO_4$ solutions. It was found that the NTR-729 membrane was negatively charged. The rejection of $Mg^{2+}$ ions in model solution of lactate was over 80% with lactate concentrations. But the rejection of $Mg^{2+}$ ions in fermentation broth of lactate was about 40 %. This results was caused by anions paired with $Mg^{2+}$ ions. It was found that the repulsive force of monovalent anions with membrane was almost few through an experiment of a mixed solution of NaCl/ $Na_2SO_4$. So the rejection of $Mg^{2+}$ ion in a fermentation broth was lower than that in a model solution because $Mg^{2+}$ ions permeated to the membrane with various monovalent anions.

• Microbiology and Biotechnology Letters
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• v.27 no.4
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• pp.320-326
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• 1999

The effects of operating pressure, lactate concentration, impurities, and pH on solution flux and lactate rejection in nanofiltration were investigated with model sodium lactate solutions (lactate 10~200g/L) as a model system. In the tested range of pressure(80~140 psig), the solution flux was observed to be proportional to the operating pressure and the rejection of lactate increased only slightly with the pressure. Both of the flux and the rejection decreased with lactate concentration, while the recovery rate of lactate increased. The effects of glucose and yeast extract as impurities on lactate rejection were negligible, but the flux decreased significantly with the addition of yeast extract. At low lactate concentrations, the rejection of lactate increased with pH due to the increased repulsion (Donnan exclusion effect) between lactate ions and membrane surface. But, at high lactate concentrations, the donnan effect was observed to be overwhelmed by the effect of sodium ions added to adjust the pH, and the rejection of lactate decreased with pH. When fermentation broth containing about 89g/L of lactate was nanofiltered, the flux and the rejection of lactate were 2.8L/$m^2$h and 5%, respectively at 120psig. Both of them were slightly lower than those with model solutions. The recovery rate was 2.6mol/$m^2$h.

• Biotechnology and Bioprocess Engineering:BBE
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• v.11 no.4
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• pp.313-318
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• 2006

A two-stage process of nanofiltration and water-splitting electrodialysis was investigated for lactic acid recovery from fermentation broth. In this process, sodium lactate is isolated from fermentation broth in the first stage of nanofiltration by using an NTR-729HF membrane, and then is converted to lactic acid in the second stage by water-splitting electrodialysis. To determine the optimal operating conditions for nanofiltration, the effects of pressure, lactate concentration, pH, and known added impurities were studied. Lactate rejection was less than 5%, magnesium rejection approximated 45%, and calcium rejection was at 40%. In subsequent water-splitting electrodialysis, both the sodium lactate conversion to lactic acid and sodium hydroxide recovery, were about 95%, with a power requirement of $0.9{\sim}1.0\; kWh$ per kg of lactate.