Cross-flow filtration of fruit juice

Conclusion

The results achieved during this project indicate that:

Filtomat thread filters can be successfully used to produce black currant juice of excellent quality. Further microfiltration is required when filtering sour cherry juice. Good performance and high fluxes are achieved with these filters.

Filtomat thread filters can replace the vacuum filter when filtering black currant juice. This results in higher fluxes and a better quality of the juice obtained (avoidance of the precipitation of polyphenols).

Polymeric membranes from X-Flow are suitable for further clarification of sour cherry juice. High fluxes (200-300 l/h/m2 for 10 hours) at low temperatures are achieved with this type of filters. Furthermore, it is more profitable to use a MF08 membrane than a MF05 for this purpose.

The backshock technique has a positive effect on the microfiltration performance reducing fouling and resulting in higher fluxes. The backshock frequency has a significant effect on the filtration duration; 3 s is the optimal value.

The cause for pore blocking is the amount of juice filtered, and not the concentration.

The ceramic membranes used in this project should be further developed.

The shadow effect does not result in problems when scaling up, whereas the pressure distribution and the control of the backshock should be further investigated.

The nature of the foulants is complex and a complex cleaning procedure is required at the moment. The role of the sugars in the membrane fouling should be further investigated, and the use of phosphoric acid when cleaning the membranes should be avoided.

High power ultrasound is a feasible method to control fouling when filtering sour cherry juice with microfiltration membranes. Filtration resistance decreases when ultrasonic power is applied above cavitation level. There is a linear relation between the filtration resistance and ultrasonic power up to a limit.

The new technology - that is pre-filtration with the Filtomat filter and the final filtration with the crossflow filtration unit – gives lower production cost and is better for the environment compared with the filtrationsystem used today.