Valorization of biogas digestate as organic fertilizer for closing the loop on the economic viability to develop biogas projects in Colombia
Camila Grandas Tavera, Thomas Raab, Laura Holguin Trujillo
Abstract
This study aims to find the best digestate valorization pathway in the Colombian context in order to foster biogas (BG) projects' economic viability and their sustainability. The GICON's BG power plant is intended to treat 19,710 t/y of fruit and vegetable wastes (FVW) from local wholesale markets in Cali, Colombia. Experimental feedstock and digestate characterization carried by Universidad ICESI and CIAT, integration of mass, energy, and nutrient balances of residues with the methodological approach based on structural analysis and expert's survey allowed further assessment of the BG project's economic viability on the proposed digestate valorization framework. Results suggested a significant profit by selling treated digestate through the vacuum evaporation (VE) technology. VE concentrated 27% of nitrogen, 18% of phosphorus, and 33% potassium of the feedstock. Furthermore, it reduced the volume of water, facilitating product transportation and making the product commercially attractive. This alternative exhibited the highest revenue for the BG project, and its expenses were slightly higher than the ones calculated for raw and separated digestate. Also, a positive return of the investment and financially worthiness could be expected, making the project economically feasible. These results provide a useful tool to evaluate future events and serve as a reference to support the BG project's viability by integrating them with the BG project's financial model and adapt the required conditions for desirable technologies.