Improving the Biogas Generation Potential from Organic Wastes Using Hydrochar as an Additive Lab-Scale Case Study from Central Sweden: Part 2

In Part 2 of the two-part series, single-stage anaerobic co-digestion in two continuously fed reactors replaced the batch process of Part 1. A life-cycle costing analysis was carried out to determine if, investing in a hydrothermal carbonization (HTC) system to produce hydrochar in-plant to augment biogas production will be economically feasible. Hydrochar addition resulted in a 59% rise in biogas yield (and 53.5% in methane yield). The study confirmed the techno-economic feasibility for coupling an HTC plant with a digester supplying 25% of the digestate it produces, to the former, as the raw material for hydrochar production. The rest of the digestate (rich in carbon, nitrogen, and phosphorus) can be used as fertiliser. Investing in an HTC plant contributing to a rise in methane production of 17% (or 53%) will result in a net profit of 363 million SEK (or 1237 million SEK) over a 20-year period. If the Karlskoga biogas plant decides to rely on purchasing hydrochar from the external market instead, the corresponding net profit will be 177 million SEK (or 1052 million SEK) over the same 20-year period, implying that a decision to integrate and interconnect is likely to be economically more feasible, in a circular bioeconomy in the future.