Economic assessment of different biogas digestate processing technologies: A scenario-based analysis

The digestate of biogas plants is a nutrient-rich product whose value can be increased by processing to improve transportability and transform it into a saleable fertilizer or soil amendment which is also called for due to nutrient surpluses in many regions and increasingly strict legislation. The limited focus of past research on processing costs of different technologies alone has left operators with scant guidance for investment decisions on digestate processing technologies. To remedy this, we performed a Net Present Value (NPV) analysis of six different digestate processing technologies to assess the economic viability of these treatments to a small (500 kW) and large (2000 kw) plant, with different heat costs, variable revenues, and variable share of transport and distribution costs borne by the plant. We focused primarily on phosphorous removal. Our results show that scenarios in which investments in processing technology yield positive returns are few. Technologies requiring heat always exhibit a negative NPV if heat is not free, even if the volume reducing benefit of these technologies is leveraged by high costs for transport and distribution. Membrane technologies exhibit a positive NPV only if transport and distribution costs for the biogas plant are high, while stripping technology is financially attractive only if the processing objective is to remove nitrogen. These results can help plant operators evaluate options for their plant. Policy makers will gain insight into the boundary conditions under which biogas plants have to operate to comply with stricter fertilizer regulations. (C) 2020 Elsevier Ltd. All rights reserved.