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Valorization of microalgal biomass by hydrothermal carbonization and anaerobic digestion

Marin-Batista, J.D., Villamil, J.A., Rodriguez, J.J., Mohedano, A.F., de la Rubia, M.A.
Bioresource technology 2019 v.274 pp. 395-402
anaerobic digestion, biomass, carbon, energy, energy recovery, hot water treatment, hydrochars, hydrochloric acid, hydrothermal carbonization, liquids, methane, methane production, microalgae, washing
The potential of hydrothermal carbonization (HTC) as a novel choice for treating microalgal biomass (MAB) was assessed. The hydrochar obtained at 210 °C had a carbon content and a higher heating value (HHV) 1.09 and 1.1 times greater, respectively, than that of the feedstock. Also, washing the hydrochar with HCl efficiently removed ash and increased its carbon content 1.40-fold. Energy recovery in the liquid fraction from the hydrothermal treatment (LF) by anaerobic digestion (AD) allowed methane yields of 188–356 mL STP CH4 g−1 VSadded, to be obtained. As a result, the amount of energy recovered from MAB was increased from about 4 MJ kg−1 (20% in terms of HHV) to 15.4, 12.1 and 10.4 MJ kg−1 by combining HTC at 180, 210 and 240 °C, respectively, with AD. Therefore, HTC at 180 °C in combination with AD seemingly provides an effective method for valorizing MAB.