Algae-derived synthetic coal and filtrates. The invention described herein provides an algae-derived synthetic coal product and filtrates and process for preparing the same using an improved hydrothermal carbonization process. The synthetic coal product is similar to natural bituminous coal in terms of percent carbon content and energy equivalency while at the same time containing relatively low levels of sulfur and contaminant heavy metals. Unlike natural coal and other fossil fuels, because the carbon of the biomass is formed through photosynthesis, carbon dioxide formed during combustion is a “carbon neutral” event with little or no “new” carbon dioxide being added to the earth's atmosphere. The algae-derived filtrates contain useful constituents.