Juices, Sugars and Starches

Sugar refining processes, purification and concentration of juices (tomato, apple, red fruits) or sugar extracts are just one of many examples of the what can be pursued with membrane technology

Membrane separation processes involving cross flow filtration have been used for a long time for the treatment of many sugary solutions. This kind of membrane processes have features that make it suitable for this sort of products:

• High flexibility, depending on the combination of the size of the pores the membrane has and the shapes and construcion details some components have.
• Low energetic effort
• Hygiene and microbiological control
• Restrained mechanical and thermical stress of the product

The applications already developed on an industrial level are sundry and very different in their nature:

• Clarification
• Purification/discoloration
• Concentration

Some of the different sugary solution treated with this kind of method are:

• Sugary juices (mainly cane sugar), clarification and discoloration
• Elementary sugars, puirfication and concentration
• Fruit washing solutions, concentration
• Pipes and tanks washing solutions, concentration
• Musts and syrups, concentration

As a supplier of membranes and technology, Sepra S.r.l. worked in all of these fields collaborating with installers who are active in the food and beverage field and primary manufacturing companies.

To test the feasibility of specific projects Sepra has at its disposal pilot plants and qualified personnel.

Washing solutions' concentration

Regarding washing solutions' concentration, membrane processes are an effective and inexpensive way of reaching concentrations acceptable for their reusal. The solution is fed to a semipermeable membrane, obtaining a concentrated fraction and a higly pure permeate. The membrane is kept clean by the continuos turbulent regime in wich the solution is constantly flowing.

Nanofiltration or low rejection reverse osmosis are commonly used especially in this field of applications. The graph shown underlines how nanofiltration membranes (Deseal D series, DK for high rejection and DL for high permeate flow) are able to guarantee high retainment of elementary sugars. This allows to have a permeate compatible with other traditional depuration plants and a concentrate containing most of the organic part of the starting solution.

A low operating pressure and a higher stability of the operating conditions represent the advantages of nanofiltration against reverse osmosis.

Osmotic pressure and the solution's levels of contamination are the limiting factor regarding the attainable concentration levels.

Expanding on the first issue, we underline that membrane processes allow to reach sugar concentrations as high as 20° Brix. Higher concentrations would be reachable, but with economically unfeasible operating pressures (>100 bar).

A more critical issue is the quality of the solution to be treated, in terms of contamination from other pollutants. Suspended solids or macromolecules are the typical cause of mebrane interference, especially when using elements in a spiral wound configuration.

When treating washing solutions which contain some relevant levevel of pollutants, an adeguate pretreatment is necessary, usually a mechanical prefiltration. In extreme cases the nanofiltration section is placed after a microfiltration section with ceramic tubular membranes.

Attention should always be paid to the concentrate created in the process. In fact, with the use of appropriate membranes, the permeate is going to have compatible features with the sewage network's rules and the concentrate can turn from a cost (disposal) to resource (can be sold as byproduct) given that the choice of process was valid.
In order to create concentrates compatible for use in animal feed, distillations and other similar applications, the issues regarding the starting solutions that must be considered are: organic composition, unwanted compounds concentrations and microbiological pollutants. The reusage of the concentrates makes non-profit projects worth funding when involved with EU assets promoting the increase of environmental efficiency of productive processes.

Conclusions

The treatment of sugary solutions is a concrete and economically attractive perspective, especially when the concentrate is valuable.

However, every process has its own peculiaruities, especially in terms of the non sugary compounds in the solution, and must therefore be approached with the background a multistaged study.

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