Making agro products from green raw materials often results in residual flows, which include both valuable components and interferants. The trick is to remove these substances from the biomass flows in such a way that the residue or interferant can be processed at the highest possible quality. To do so, Wageningen Food & Biobased Research has a wide range of separation techniques in house and also develops new technologies for applications within the circular economy.
A residual flow such as sugar beet leaf would be a good biobased fuel if it did not contain as much potassium. In incinerators, this type of salt has the troublesome property that it can coagulate in unwanted places after melting and cause major damage. Another example of an interferant is chlorogenic acid in sunflower seeds. Failure to remove the substance from sunflower seed flour means that bread colours black or green. Chlorogenic acid also lowers the nutritional value of the bread or the value of the animal feed in which it is processed by damaging the most useful amino acids. Watery flows such as drainage from agriculture or horticulture often contain many valuable or harmful components too. Nutrients added by the farmer should preferably be preserved for reuse while residues of crop protection agents should be removed from the water before discharge.
Solutions using separation technology
The question is: how can one get rid of these and other interferants? “There are various methods available,” says Wilfred Appelman, expertise leader in Separation & Purification at Wageningen Food & Biobased Research. A non-comprehensive overview: “There are various techniques, often based on hybrid membrane processes, that we can use to dewater biomass flows in a far-reaching and energy-efficient way. Electrically powered separation processes such as electrodialysis and capacitive deionisation are used to extract salts from water, in which we can separate potassium, phosphate and magnesium and even convert them into acids and alkalis. A high-quality application that is often used in the dairy and pharmaceutical industry, for example, is Ion Exclusion Chromatography. This allows us to perform very specific separations at the molecular level and isolate valuable components, such as proteins, sugars, and colourants, aromatics and flavouring agents.”
A new method for the constant separation of interferants with the minimal use of excipients is counter-current extraction, developed by Wageningen co-scientist Koen Meesters. “You can compare the extraction to making coffee,” Meesters explains. “In this process, a fluid – water – is heated and poured over a solid substance – ground coffee beans. The residue is coffee grounds. If you use these grounds to make coffee five more times, you may extract all the aromas but eventually end up with very watery coffee. In counter-current extraction we use the water from the final extraction step and pour it over the not entirely depleted coffee grounds. We then use this water again for the remaining residue from the previous step. Finally, we pour the same water over the fresh coffee powder. This creates an optimal extraction process, in which you achieve full extraction with much less water.”
Reducing the phosphate problem
The test installation in the lab at Wageningen Food & Biobased Research is running at full power to test counter-current extraction on a wide variety of residual flows. This ranges from the extraction of valuable substances from empty fruit bunches of the oil palm (which plantations throw on a heap to rot), to the extraction of phosphate and nitrogen from brewers’ grains, rapeseed press cake and canola press cake. And there are plenty of opportunities there, Meesters expects. “Everyone is for the use of agro residual flows as a biobased fuel to replace fossil fuel. At the moment, this is mainly achieved with soy scrap from imported soy used for animal feed. This import significantly contributes to the Dutch phosphate excess. If we were to use Dutch crops instead of soy and were able to remove the phosphate it would immediately reduce the phosphate problem.”
And the costs? “This is often an issue for companies,” says Appelman “But thanks to our wide range of technologies we are often able to extract interferants in a cost-effective way.”