Hydrothermal treatment can convert paper mill biological (bio-) sludge waste into more energy-dense hydrochar, which can achieve energy savings and fossil CO2 emissions reduction when used for metallurgical applications. This study assesses the basic, combustion and safety performance of bio-sludge hydrochar (BSHC) to evaluate its feasibility of use in blast furnace injection processes. When compared to bituminous and anthracite coals, BSHC has high volatile matter and ash content, and low fixed carbon content, calorific value and ignition point. The Ti and Tf values of BSHC are lower and the combustion time longer compared to coal. The R0.5 value of BSHC is 5.27 × 10−4 s−1, indicating a better combustion performance than coal. A mixture of BSHC and anthracite reduces the ignition point and improves the ignition and combustion performance of anthracite: an equal mixture of BSHC and anthracite has a R0.5 of 3.35 × 10−4 s−1. The explosiveness of BSHC and bituminous coal is 800 mm, while the explosiveness of anthracite is 0 mm. A mixture of 30% BSHC in anthracite results in a maximum explosiveness value of 10 mm, contributing to safer use of BSHC. Mixing BSHC and anthracite is promising for improving combustion performance in a blast furnace while maintaining safe conditions.