Journal
ENERGY CONVERSION AND MANAGEMENT
Volume 196, Issue -, Pages 1385-1394Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.enconman.2019.06.044
Keywords
Macroalgae; Hydrothermal pretreatment; Energy efficiency; Biohydrogen; Biomethane
Categories
Funding
- European Union [797259]
- Environmental Protection Agency - Ireland [2018-RE-MS-13]
- Science Foundation Ireland (SFI) through the Centre for Marine and Renewable Energy (MaREI) [12/RC/2302, 16/SP/3829]
- ERVIA
- Gas Networks Ireland (GNI) through the Gas Innovation Group
- Marie Curie Actions (MSCA) [797259] Funding Source: Marie Curie Actions (MSCA)
- Environmental Protection Agency Ireland (EPA) [2018-RE-MS-13] Funding Source: Environmental Protection Agency Ireland (EPA)
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Marine macroalgae (seaweed) is a promising feedstock for producing biohydrogen and biomethane via dark fermentation and anaerobic digestion, respectively. However, one of the limiting steps in the biological process is the conversion of polymeric carbohydrates into monomeric sugars. Here hydrothermal pretreatments were assessed for hydrolysis and subsequent production of biohydrogen and biomethane from the brown seaweed Saccharina latissima. The solubilization of S. latissima improved with increasing temperatures from 100 to 180 degrees C, resulting in a maximum yield of 0.70 g soluble chemical oxygen demand/gram volatile solid (sCOD/g VS); equivalent to an increase of 207.5% compared with untreated seaweed. However, the yield of the derived monomeric sugar mannitol peaked at 140 degrees C and decreased with increasing temperatures, likely due to production of fermentative inhibitors. Microstructural characterization revealed that the algal structure was significantly damaged, and the major chemical groups of carbohydrates and proteins were weakened after pretreatment. Regardless of hydrothermal temperatures, biohydrogen yield only slightly increased in dark fermentation, while biomethane yield significantly increased from 281.4 (untreated S. latissima) to 345.1 mL/g VS (treated at 140 degrees C), leading to the sCOD removal efficiency of 86.1%. The maximum energy conversion efficiency of 72.8% was achieved after two-stage biohydrogen and biomethane co-production. In comparison, considering the energy input for pretreatment/fermentation/digestion, the highest process energy efficiency dropped to 37.8%. Further calculations suggest that a significant improvement of efficiency up to 56.9% can be achieved if the heat from pretreatment can be recovered.
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