Potential of the sewage sludge valorization in Scandinavia by co-digestion with other organic wastes: A techno-economic assessment

Abstract

The aim of this study was to compare the techno-economic feasibility of five different scenarios to valorize sewage sludge in co-digestion with another organic waste. The first three scenarios were based on real full-scale processes in Scandinavia, furthermore two original biorefinery scenarios for carboxylates and biogas production were proposed. Data from the actual plant of one scenario was used in order to calibrate the simulation, creating five realistic models for sludge valorization. Two downstream technologies were simulated for the valorization of carboxylates: anion exchange chromatography and biological separation (through PHA production). Even though none of the models was profitable without subsidies, the biorefinery scenario with biological separation was the most promising one, with the operating costs (2.79 million €) closest to the total revenues (0.8 million €). The use of anion exchange chromatography created an economic bottleneck in the model (57% of the operating costs), suggesting the need for more simple and cost-effective downstream technologies, when developing biorefineries for the valorization of waste streams. Moreover, the importance of public subsidies, gate fees for organic wastes and the amount of treated material were found to be key aspects for the economic feasibility of these facilities treating waste, increasing the total revenues between 2 and 15 times, depending on the modelled scenario.