Synthetic coalification of microalgae through hydrothermal carbonization: strategies for enhanced hydrochar...

This review explores the hydrothermal carbonization (HTC) of microalgae through a comprehensive evaluation of the influence of process parameters on the resultant products. The findings revealed that HTC of microalgae takes place at lower temperatures (170 - 250 °C) compared to lignocellulosic feedstocks, and the resulting hydrochar and hydrolysate have a higher N-content. Additionally, secondary char production varies based on reaction conditions, with yields between 4 % and 35 %. The interaction between carbohydrates and nitrogenous compounds in the hydrolysate at varying reaction severities was discussed, underlining the extent of nitrogen fixation in the hydrochar and total organic C-content of up to 26.8 g L^-1. The article also suggests strategies to improve hydrochar properties by assessing different technical strategies and emphasizing future direction research. In summary, this review underscores the potential of microalgal HTC as a sustainable approach for applications in energy and environmental applications via process optimization and technological upgradation.