At Biogasbolaget AB in Karlskoga in south-central Sweden, organic wastes like food waste, manure, and silage are digested anaerobically to yield biogas, which subsequently can be upgraded to biomethane, and used as a replacement for fossil-diesel in public transport. The digesters at the firm are currently operating below their maximum capacity. This chapter deals with the evaluation of the potential of hydrochar to augment biogas production in a batch process. Hydrochar produced from two sources – forestry sector and municipal organic wastes – were compared, and using the Automatic Methane Potential Testing System (AMPTS II) in the lab at Karlstad University, the optimal dosage was determined. Experiments were also conducted with hydrochar alone, to verify if the hydrochar was being anaerobically digested to yield biogas. The hydrochar sourced from municipal waste, when dosed at 8 g/l, produced 841 Nml of biogas /gram of VS (volatile solids) in the substrate, 93% greater than the reference case of no addition of hydrochar. The forestry-sector-sourced hydrochar on the other hand, at the same dosage, registered an increase of just 16.6%. A streamlined environmental life-cycle analysis showed that significant climate-benefits can be availed of, implying environmental sustainability, when the additional biogas is refined and used to replace fossil-diesel in public bus transport. Hydrochar-assisted anaerobic digestion of organic wastes may be posited as a technology which may entrench itself in the circular bio-economies of tomorrow, around the world, and bywhile doing so, contribute to a set of sustainable development goals. While these were batch-digestion experiments, this part of the two-part series recommends more-realistic continuous-digestion experiments which incidentally form the focus of Part 2.