Assessing the treatment costs and the fertilizing value of the output products in digestate treatment systems

The objective of this paper was to advance towards finding sustainable solutions to deal with biogas digestate and contribute to faster development of the market for digestate treatment products. The study compares digestate treatment costs through four different treatment plants, estimates the potential fertilizing and humus value (PFHV) of the derived products and allocates the cash flows to show the possible regional benefits. The treatment costs for the pre-dried solid fraction of digestate ranged from €19 to €23/tonne output. These costs may be covered by vending treatment products at a price reaching at least 34-41% of their PFHV (ca €55/tonne). Treatment of raw digestate generates high operating costs (€216-247/tonne output), much higher than the PFHV of the products (ca €35- 51/tonne). For such systems either the treatment has to be financially subsidized by the authorities or €13-32/tonne input should be covered by the substrate deliverers as a disposal fee. Nevertheless, a well-prepared investment concept in this field may allow the local binding of up to 80% of total cash flows. Finally, the current difficult market situation of the treatment products can be primarily improved by clearing their legal status at European level.