Experiment of treating aspartame hypersaline amino acids wastewater using nanofiltration membrane

Abstract: In order to obtain the appropriate operating parameters in treating aspartame hypersaline amino acids wastewater using nanofiltration membrane, the experimental device was built. Experimental investigation was carried out to explore the separation performance of average permeate flux, the volume concentration ratio，amino acid retention, sodium chloride removal rate and amino acid recovery rate under different experimental conditions. Experimental parameter conditions were as follows: when inlet pressure was 1.6, 2.0, 2.4, 2.8, 3.2 MPa, pH value was 6.8~7.5, temperature was 40℃ and feed flow rate was 0.1m/s; when temperature was 30, 35, 40, 45, 50 ℃, inlet pressure was 2.4 MPa, pH value was 6.8~7.5 and feed flow rate was 0.1 m/s; when pH value was 2, 3, 6, 8, 10, inlet pressure was 2.4 MPa, temperature was 40℃ and feed flow rate was 0.1m/s; when feed flow rate was 0.02, 0.05, 0.10, 0.15, 0.20 m/s, pressure was 2.4 MPa, temperature was 40℃, pH value was 6.8~7.5. The results show that the inlet pressure, temperature, pH and feed flow rate have different effects on nanofiltration membrane separation performance. When inlet pressure increases, the average permeate flux, volume concentration ratio，sodium chloride removal rate and amino acid retention increase, while amino acid recovery rate decreases slightly. When temperature increases, average permeate flux, volume concentration ratio and sodium chloride removal rate increase, while amino acid retention and amino acid recovery rate decrease. When pH value increases, average permeate flux, volume concentration ratio and sodium chloride removal rate increase, and there is a peak in pH value of 6. Then with the increase of pH value, average permeate flux, volume concentration ratio and sodium chloride removal rate decrease, while amino acid retention and amino acid recovery rate increase. When feed flow rate increases, average permeate flux, volume concentration ratio，sodium chloride removal rate increase. But when feed flow rate is greater than 0.1 m/s, they tend to be stable. The feed flow rate has a little effect on amino acid retention and amino acid recovery rate. The appropriate operating parameters are the inlet pressure of 2.4 MPa, pH value of 6, the temperature of 40 ℃ and the inlet flow rate of 0.1 m/s. Under the conditions, the system of nanofiltration membrane works for 3 hours, the average permeate flux is 21.5 L/（m2·h）, the volume concentration ratio is 5.9, the sodium chloride removal rate is 96%，the retentions of L-phenylalanine and L-aspartic are 89% and 77% respectively，the recovery rates of L-phenylalanine and L-aspartic acid are 90.6% and 80.3% respectively．The experimental researches provide the reference for industrial application of nanofiltration membrane in treating aspartame hypersaline amino acids wastewater.