The characteristics of bioliquid produced through the hydrothermal carbonization (HTC) of wood wastes and the effects of recirculation on hydrochar production were analyzed. The organic acids and total organic carbon of bioliquid increased with progressive recirculation, whereas intermediate byproducts decreased. Hydrochar production by bioliquid recirculation increased mass yield, carbon content, caloric value, and energy yield of the former, while improving its quality as a solid refuse fuel. We concluded that bioliquid recirculation promoted HTC, as demonstrated by Fourier-transform infrared spectroscopy. Furthermore, contrary to predictions, a relatively constant quantity of bioliquid was generated in each step, indicating that its continuous reuse is feasible. Therefore, bioliquid recirculation can improve hydrochar production while simultaneously mitigating the environmental impact of wastewater generation. This method should be considered an important strategy toward the implementation of carbon-neutrality goals.

The increasing adoption of electric vehicles (EVs) has highlighted the need for sustainable lithium-ion battery (LIB) management. This study presents a material flow analysis (MFA) of EV LIBs in the Republic of Korea (RoK), using both a mass-based MFA and a substance flow analysis (SFA). The analysis defines 33 systems and 170 flows across the manufacturing, consumption, discharge and collection, and treatment stages, based on national statistics and data from 11 commercial facilities. In 2022, about 72,446 t of EV LIBs entered the consumption stage through new vehicle sales and battery replacements. However, domestic recovery was limited, as approximately 76.5% of used EVs were exported, reducing the volume of batteries available for recycling. The SFA, focusing on nickel (Ni), cobalt (Co), manganese (Mn), and lithium (Li), showed recovery rates of 69% for Ni, 80% for Co, 1% for Mn, and 80% for Li. Mn was not recovered because its low market price made the recovery process economically impractical. Additional losses occurred from the incineration of separators containing black mass and lithium discharged through wastewater. These findings offer data-driven insights to improve recovery efficiency, guide policy, and enhance the circularity of EV LIB management in the RoK.