Search

Marine algal biofuel is considered a promising solution for energy and environmental challenges. Macroalgal biomass has the potential for bypassing the shortcoming of first and second generation of biomass from food crop and lignocellulosic sources. In this review, we summarize the findings in this domain in the past two decades with a focus on the process of saccharification and fermentation of macroalgae for transportation biofuels. In general, macroalgae contains high levels of carbohydrates, almost no or comparatively less lignin than in terrestrial plants, which makes it a very promising source for liquid biofuel production via bioconversion. After harvest, macroalgal biomass goes through several process units, including pre-treatment and/or saccharification and fermentation to be converted to biofuel, e.g., bioethanol. We also propose strategies for further studies to realize macroalgae biomass potential for transportation bioenergy production. [ABSTRACT FROM AUTHOR]

• Solar-thermal seaweed biorefinery with offshore intensively grown biomass was analysed. • Co-production of protein, hydrochar, ethanol, distilled water and electricity was analysed. • The overall First Law efficiency is 32% and can reach 40% with energy recovery from aqueous phase. • Seaweed, electricity and protein prices are key for the profitability of the biorefinery. • The lowest environmental impacts are achieved with HDPV cage, PV electricity, and rail transport. Combing solar energy with biomass processing facilities are emerging systems for efficient use of solar energy for electricity generation, energy storage, and production of renewable materials. In this work, we propose a novel combination of solar thermal energy systems with marine macroalgae biorefinery, which requires energy inputs for biomass cultivation and processing. In this work, we analyze a 10-ton dry weight per hour capacity pilot-scale hybrid solar seaweed biorefinery, located at the Mishor Rotem near Dimona, the current location for solar-thermal projects in Israel, where seaweed biomass supply comes from a hypothetical offshore farm located 15 km offshore. Our energy and mass balance analysis show that the overall First Law efficiency of the hybrid solar seaweed biorefinery system for the co-production of protein, hydrochar, ethanol, distilled water, and electricity is 32% and can exceed 40% with additional waste stream recycling. Our cost-benefit analysis of the proposed solar-seaweed biorefinery shows that the prices of seaweed, electricity, and protein are the key drivers of the profitability of the production process. The environmental impacts of the hybrid solar-seaweed biorefinery with intensified offshore cultivated biomass were quantified under various seaweed cultivation, transportation, and processing strategies. [ABSTRACT FROM AUTHOR]

Offshore grown macroalgae biomass could provide a sustainable feedstock for biorefineries. However, tools to assess its potential for producing biofuels, food and chemicals are limited. In this work, we determined the net annual primary productivity (NPP) for Ulva sp. (Chlorophyta), using a single layer cultivation in a shallow, coastal site in Israel. We also evaluated the implied potential bioethanol production under literature based conversion rates. Overall, the daily growth rate of Ulva sp. was 4.5 ± 1.1%, corresponding to an annual average productivity of 5.8 ± 1.5 g DW m −2 day −1 . In comparison, laboratory experiments showed that under nutrients saturation conditions Ulva sp. daily growth rate achieved 33 ± 6%. The average NPP of Ulva sp . offshore was 838 ± 201 g C m −2 year −1 , which is higher than the global average of 290 g C m −2 year −1 NPP estimated for terrestrial biomass in the Middle East. These results position Ulva sp. at the high end of potential crops for bioenergy under the prevailing conditions of the Eastern Mediterranean Sea. We found that with 90% confidence, with the respect to the conversion distribution, the annual ethanol production from Ulva sp. biomass, grown in a layer reactor is 229.5 g ethanol m −2 year −1 .This translates to an energy density of 5.74 MJ m −2 year −1 and power density of 0.18 W m −2 . Growth intensification, to the rates observed at the laboratory conditions, with currently reported conversion yields, could increase, with 90% confidence, the annual ethanol production density of Ulva sp. to 1735 g ethanol m −2 year −1 , which translates to an energy density of 43.5 MJ m −2 year −1 and a power density 1.36 W m −2 . Based on the measured NPP, we estimated the size of offshore area allocation required to provide biomass for bioethanol sufficient to replace 5–100% of oil used in transportation in Israel. We also performed a sensitivity analysis on the biomass productivity, national CO 2 emissions reduction, ethanol potential, feedstock costs and sizes of the required allocated areas. [ABSTRACT FROM AUTHOR]

• Hydrothermal processing of the whole Ulva sp. biomass vs. extracted carbohydrate fractions of starch and cellulose. • Glucose is a major released monosaccharide with hydrothermal deconstruction. • Most of the glucose is released from starch. • Whole biomass hydrolysis preferred for PHA fermentation with Haloferax mediterranei. • The highest ash-free hydrochar yield was from Ulva cellulose. In the fermentation and bioenergy industry, terrestrial biomass is usually fractionated and the collected components, such as starch, are processed separately. Such a separation has not been reported for seaweeds. In this work, the direct hydrothermal processing of the whole green seaweed Ulva sp. biomass is compared to processing of separated starch and cellulose, to find the preferable route for monosaccharide, hydrochar, and polyhydroxyalkanoates (PHA) production. Glucose was the major released monosaccharide. A significant share of the glucose yield comes from the starch fraction. The highest hydrochar yield with the lowest ash content was obtained from the separated cellulose fraction. The highest PHA yield was obtained using a whole Ulva sp. hydrolysate fermentation with Haloferax mediterranei. Economic analysis shows the advantage of direct Ulva sp. biomass fermentation to PHA. The co-production of glucose and hydrochar does not add significant economic benefits to the process under plausible prices of the two outputs. [ABSTRACT FROM AUTHOR]