| Abstrakt: |
Introduction: High cost, energy, and water consumption, waste discharge, and environmental pollution of conventional clarification and decolorization methods of fruit syrups such as using lime, resin, and activated carbon affected greatly their efficiency and effectiveness. Therefore, membran e-based process has gradually become an efficient separation technique for the purification, clarification, and concentration of various fruit syrups due to its unique separation capabilities, high output, and low energy consumption. The main problem associated with the membrane-based separation process is the reduction of permeate flux during operation due to concentration polarization and membrane fouling. Cake or gel layer formation on the surface of the membrane, increasing the osmotic pressure at the i nterface between the membrane and the solution and or reducing the effective driving force are the results of concentration polarization. The membrane fouling causes membrane destruction, reducing productivity, and increases operating costs for washing and replacing the membrane. On the other hand, the use of membrane purification and clarification of date liquid sugar is of great importance because it excludes the use of chemicals in the clarification of this product and produces an added value and superio r quality product. The aim of this study is to prepare clarified date liquid sugar from depectinized date syrup. In addition, the effects of different ultrafiltration feed parameters (pressure, flow rate and temperature) on the permeate flux and fouling mechanisms were investigated. Hermia models were used to interpret the membrane pore blocking conditions in order to investigate the details of the fouling mechanism. Materials and Methods: Polysulfone membrane with effective surface area (0.0096 m2 ), pore sizes (30- 40 nm), MWCO (3 -3.5 kDa), and initial flux (3-20 kg/ (m2 .h), pure water at 25 °C, 1 bar) was used for ultrafiltration of depectinized date juice (DDJ). DDJ was purchased from Pars Minoo Industrial Company, Tehran, Iran. The feed solution for the ultrafiltration clarification was prepared by adjusting the DDJ concentration to 11.5 wt% using deionized water. The different operating conditions include two temperature levels (27 and 40 °C) and three pressure levels (1, 1.5 and 2 bar) and three flow r ate levels (10, 15 and 20 ml/s), were performed. The mass of permeate flux as the main output parameter of UF was determined by measuring its weight change over UF time ∆t. Hermia models, including standard pore blocking, complete pore blocking, intermediate pore blocking and cake filtration are used to predict the fouling mechanism of membrane due to purification and clarification processes. Results and discussion: Clarification of date syrup in different operating conditions in 16 different modes were done with ultrafiltration process. The results revealed that the temperature, pressure and flow rate have a significant effect on the permeate flux and the final achieved transparency. Therefore, the effectiveness of the operating conditions on ultrafiltration membrane fouling mechanism based on Hermia models were investigated in the plot form to specify the different parameters of the models. The results showed that the change in the operating conditions will cause a change in the membrane fouling mechanism. Cake filtration, intermediate pore blocking, and standard pore blocking were the evaluated membrane fouling mechanism in the considered operating conditions in this study. In the most examined conditions, the cake filtration mechanism was identified as the dominant mechanism of membrane fouling in the ultrafiltration clarification process of date syrup.The comparison of the physicochemical properties of clarified date syrup under the selected conditions (pressure 1.5 bar, temperature 40°C and flow rate 10 ml/s with the highest permeated flux) shows the reduction of TPC, TSS, turbidity and pectin in the final product. Compared to the feed, they were 32.06%, 8.3%, 83.4% and 99.5%, respectively. As well, L* parameter value increased from 28.77 to 48.11 during the ultrafiltration process, and a* and b* parameters decreased from 3.49 to 0.87 and 36.1 to 29.58, respectively. According to the results of this research, the use of ultrafiltration membrane process in optimal operating conditions is suggested as a suit able method for clarifying date syrup. Conclusion: In this study, Hermia pore blocking models were used to evaluate membrane deposition in the clarification of date syrup with the ultrafiltration process. The results showed that by adjusting the operating conditions (including temperature, pressure and feed flow rate) ultrafiltration clarification of date syrup, it is possible to achieve proper clarity while maximizing the permeated flux, despite achieving the appropriate physicochemical properties of the product. Although the maximum permeated flux during the ultrafiltration process by choosing the optimal conditions of feed temperature and pressure affects the transparency of the final product, but the high clarification of date syrup are achieved at very low permeated flux, which it is not a cost-effective process. However, the performance of ultrafiltration process is significantly better than conventional thermal and chemical purification and clarification methods. Fouling analysis was performed for all clarification experiments using four Hermia’s models to identify the appropriate fouling mechanism. Among these four models, the cake filtration mechanism was determined as the dominant membrane blocking mechanism during the clarification process of date syrup. [ABSTRACT FROM AUTHOR] |
