Evaluation of the Fouling Phenomenon During Membrane Clarification of Apple Juice Using Scraped Surface Membrane Unit

Introduction As a useful fruit for humans, apple (Malus domestica) is a good sourceof antioxidants, minerals, ascorbic acid, vitamins, polyphenols, fibers and other essential elements with medicinal properties. Improving the storage time of apple juice and maintaining the stability of extracts with high Brix value (during transportation and storage) and its marketability by removing the remaining water as well as reducing the turbidity, viscosity and brown color caused by colloidal suspended solids. Large (pectin, protopectin, pigments, polymeric carbohydrates, tannin, starch, cellulose, hemicellulose, fibers, etc.) is of great importance. Due to the presence of colloidal suspended solid particles and compounds that settle over time (mold, bacteria, plant cell fragments, pectin-tannin complex), apple juice must be clarified before concentration. Due to the high-energy consumption, time-consuming, degradation of thermo-sensitive components, and reduction of nutritional value in traditional methods, recently, the use of membrane concentration in food and beverage production holds great potential.. Despite all the benefits of membrane processes, one of the critical problems is permeate flux decline due to the concentration polarization and membrane fouling. In this study, an innovative mechanical motion was developed to remove the cake deposits on the membrane surface towards mitigating adverse effects of polarization and fouling.   Materials and Methods Membrane scraped surface module was designed and made with polyethylene material. The membrane was enclosed between the lower and upper parts of the module. These two parts are connected with screws and create a cylindrical part. Also, two caps are pressed axially to this cylindrical part by a metal frame to eliminate any unwanted leakage. The rotor shaft was coupled with an electric motor and the rotation of the output shaft was regulated by an inverter. A pump transferred the fresh fruit juice to the module through the inlet port and then it was divided into two output streams, permeate and retentate. The permeate was collected from the bottom of the module for further investigation and the retentate was returned to the juice tank. A polyethersulfone (PES) membrane with molecular weight cut-off (MWCO) of 4 kDa was used to clarify apple juice. Effects of the blade rotation speed (0, 600, 1400 and 2200 rpm), transmembrane pressure (TMP) (0.5, 1 and 1.5 bar), feed flow rate (FFR) (10, 15 and 20 ml/s) and the distance of the blade from the membrane surface (2 and 5 mm) on volumetric concentration factor (VCF) and fouling phenomenon were evaluated. Hermia model was used to study the main fouling mechanism and it was verified by scanning electron microscopy (SEM) images.   Results and Discussion  Results showed that rotating the blade with speed of 600 rpm at TMP of 0.5 bar, FFR of 10 ml/s and 2 mm distance from the membrane surface had the best performance in VCF and reducing fouling. The main mechanism of fouling was cake formation. Rotation of the blade decreases the intensity of cake formation and its thickness on the membrane surface and enhances the standard pore blocking. Also increasing the blade rotation speed changes the main fouling mechanism to the standard pore blocking due to the cake disintegration on the membrane surface and the penetration of fine particles into the membrane pores. As a result, the rotation of blade had a significant positive effect on increasing the VCF. On the other hand, the total resistance decreased with the rotation of the blade and by increasing the distance of blade from the membrane surface, the intensity of cake formation reduced. Also, the SEM images showed that in without blade rotation mode, the accumulation of cake particles on the membrane surface is thicker and denser than in with blade rotation mode. On the other hand, the low thickness of the cake layer formed on the membrane surface in the process of blade rotation is due to the turbulences resulting from the rotating blade. These observations confirm the results of the Hermia model in the previous sections.   Conclusion  In conclusion, the TMP 0.5 bar, FFR of 10 ml/s, blade rotation speed of 600 rpm with a distance of 2 mm from membrane surface were considered as the best conditions for ultrafiltration of apple juice using scraped-surface membrane unit

The Effect of Ultrasound on Permeation Flux and Changes in Blocking Mechanisms during Dead-End Microfiltration of Carrot Juice

Carrot juice is one of the most nutritious foods that are consumed around the world. Large particles in carrot juice causing turbid appearance make some problems in the concentration process such as off-flavor due to the large particles burnt on the walls of evaporators. Microfiltration (MF) is a pressure driven membrane separation method that can clarify fruit juices without enzymatic treatment. Fouling is the main problem in the membrane process causing reduction of permeate flux. Ultrasound as a cleaning technique was applied at 20 kHz to reduce fouling in membrane clarification of carrot juice using dead-end MF system with polyvinylidene fluoride (PVDF) membrane. Results showed that application of ultrasound waves reduce diphasic characteristic of carrot juice and permeate flux increased. Evaluation of different membrane fouling mechanisms showed that application of ultrasound waves changed creation time of each fouling mechanism. Also, its behavior was changed with varying transmembrane pressure