In the Part I of this two-part series, the potential of hydrochar of two different provenances to augment biogas production in a batch process, was evaluated, using the Automatic Methane Potential Testing System (AMPTS II) in the lab at Karlstad University. In Part 2 of the two-part series, this part, single-stage anaerobic co-digestion in two continuously-fed reactors, replaced the batch process of Part 1. A The possibility of connecting an existing digester with a hydrothermal carbonization (HTC) reactor was investigated, and a life-cycle costing analysis was carried out to determine if, in addition to the environmental benefits written about in Part I, investing in an 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 pH remained stable around 7.6 throughout the digestion process. The study confirmed It will be the techno-economic feasibility for coupling an ally practical and feasible to interconnect 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 find use as fertiliser. Investing in an The LCC analysis showed that 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.