In this study, red seaweed (Gracilaria lemaneiformis) food waste with high carbohydrate content was valorized into levulinic acid (LA) and algae hydrochar through microwave-assisted low-temperature hydrothermal treatment in dilute acid solution. Various parameters including treatment temperature (160-200 degrees C), reaction time (1-40 min), acid concentration (0-0.6 M), and biomass-to-liquid ratio (1%-10%, w/v) were examined. The energy efficiency and carbon recovery of the proposed process were investigated. Under the experimental conditions of 5% (w/v) biomass loading, 0.2 M H2SO4, 180 degrees C, and 20 min, the highest levulinic acid yield of 16.3 wt% was produced. The resulting hydrochar showed approximately 45-55% energy yield and higher heating values of 19-25 MJ kg(-1). The energy efficiency of the present study (1.31 x 10(-6)g LA/J) was comparable to those of the conventional hydrothermal treatment of lignocellulosic biomass, while the reaction time (20 min) was much shorter with a high carbon recovery (73.3%).