Author: Anika Peucker | Translation: Anna Knollmann, Stephanie Anderseck

Fertiliser, water, bioenergy – dairy residues as a "one-stop shop" in a closed recycling circuit

Do you like milk? Many among us like it. On average, each of us drank about 52 litres in 2015 - according to figures from the German Dairy Industry Association. Not enough for that. On top of that came 6 kilograms of butter, 17 kilograms of yoghurt and 25 kilograms of cheese per head.

During the production of the various dairy products, residual materials are produced that cause high disposal costs, either half or unused. A pity about that! Because they are valuable, provided we can feed them into a closed recycling circuit. Up to now, the concepts for such a recycling cycle have been lacking. Recently, however, our scientists, together with Sachsenmilch Leppersdorf GmbH and wks Technik GmbH, have succeeded in validating a sophisticated process for this purpose. Now, the disposal of the residual materials no longer only consumes energy, but also produces biogas. The remaining substances are also used to produce slow-release fertilizers and water that reaches the quality of drinking water. But one after the other!

 

Granulated biomass pellets for the decomposition of organic matter and the production of biogas.
© Fraunhofer IKTS
Granulated biomass pellets for the decomposition of organic matter and the production of biogas.
Laborfermenter – Biogasreaktor im Labormaßstab.
© Fraunhofer IKTS
Laboratory fermenter – biogas reactor on a laboratory scaleLaboratory fermenter.
Produced and dried magnesium ammonium phosphate (MAP). It can be used as a direct, high-quality and slowly nutrient-releasing fertilizer.
© Fraunhofer IKTS
Produced and dried magnesium ammonium phosphate (MAP). It can be used as a direct, high-quality and slowly nutrient-releasing fertilizer.

All in all a well-rounded affair

Of course, the conversion does not take place in one step, but along a route of complex physical and bio-chemical reactions. Sachsenmilch has been producing bioethanol from molasses the residue from whey processing for some time now. Bioethanol is a component of biofuels and is used either as a petrol additive or directly for use in petrol engines. During the production of bioethanol, i.e. the alcoholic fermentation and distillation of molasses, the thin stillage, the "waste material" from this process step, remains. However, the thin stillage contains valuable organic acids and salts. And this is exactly what it is all about. We convert them into biogas, fertilizer and water. The organic substances ferment in an anaerobic environment to produce biogas – one of the most sustainable forms of bioenergy production. This requires a high-performance fermentation reactor. With this, our scientists have now achieved a degradation rate of the organic substance of more than 95 percent and a methane content in the biogas of more than 62 percent by volume in the produced biogas after several test and process optimisations. All in all a difficult process. But it was worth it: both values are above the usual levels.

In the next step, the slow-release fertilizer is produced. The scientists add reaction chemicals to the inorganic ammonium and phosphate produced during fermentation, thereby separating the two nutrients from each other. The reaction product is then a fertilizer that is particularly valuable for crops because of its phosphorus content.

The substances that are left over from fermentation are then filtered using a robust ceramic nanomembrane. This retains particles, macromolecules and higher-quality salts. By oxidation and elimination of monovalent salts via reverse osmosis, finally drinking water is produced that meets the legal quality requirements. The scientists are specifically feeding this fresh water back into the material cycle. All in all, it is a perfect deal in terms of material, energy and money.

 

Excellent – excellent!

For Sachsenmilch the cooperation has been worthwhile. What was designed on a small scale is now used to increase efficiency in the ongoing production process and intelligently recycle valuable materials. The process concept has just been awarded the "agra Prize for Innovation" in the nutritional science category. We are proud of this, because it shows us once again the relevance of the topic. But not only dairies should benefit from this value-added cycle. The aim must be to transfer it to other industrial residual material flows. You could imagine implementing a sustainable recycling cycle in your company as well? Please contact us. The approach offers ample potential. We are curious to discover your potential.

 

Further information

 

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