The decrease in biomass growth with increase of HTL temperature is
attributed to decreasing levels of carbohydrates in the AP at higher HTL
temperatures; as HTL temperature is increased more of the carbon in
the biomass feed is converted to bio-crude, bio-char and off-gases
while less of it remains in the AP that is recycled [5]. Carbohydrate
level in the AP as a function of HTL temperature shown in Fig. 2-a
confirms this supposition. A previous study of the carbon and nitrogen
products from hydrothermal liquefaction of low-lipid microalgae at
reaction temperatures greater than 220 °C resulted in 35–40% of the
carbon being converted to compounds found in the aqueous product
[26]. Broch et al. [28] also studied hydrothermal carbonization of
Spirulina and reported that total organic carbon accounted for less
than 50% of the dissolved mass