The Value of Digestate: Winning with Calcium
After three years of intensive research in cooperation with Saxion University, an innovative project by HoSt has come to a positive conclusion. Under the name ‘Kassa met Kalk’ (EN: Winning with Calcium) research was conducted to find a method to recover minerals and nutrients from the remaining digestate, the organic residue of the anaerobic digestion process. This residual valuable product is still often wrongly regarded as idle waste, so that the precious substances left behind are not put to use. That’s where this method provides the solution.
Process and R&D engineer Gijs Olde Loohuis of HoSt: “Three years ago we decided that this had to change and we joined forces with Saxion. The university has offered its laboratories to carry out fundamental research on a small scale. Saxion also had a number of enthusiastic students working with us, who contributed their expertise in the research, test and development phases. We have now achieved almost all of our objectives.”
Separating with calcium
The most important part of the project was to find the most optimal way of winning back valuable minerals and nutrients from digestate. Using calcium improves the separation efficiency. In this way, it turns out to be possible to recover nitrogen and phosphate as separate raw materials in an economically viable manner. CO2 has also been looked at, which is a weaker acid. There is an abundance of this; for example, 45% CO2 is present in biogas. This has been cleverly used to optimise nitrogen recovery.
The new way of digestate separation
The project optimized the separation process and produced a design to enable the process to be carried out. The best news according to Gijs: “It is feasible in practice and cheaper than the traditional way of removing nitrogen. So it can be used in our biogas plants!”
The study ‘Kassa met kalk’ was made possible by the European Regional Development Fund (ERDF). The ERDF is one of the European structural funds. With the ERDF, the EU wants to reduce the economic differences between the European regions.