Members of the very specie that accessed, utilized, and exploited fossil fuels for centuries, are now campaigning against it. Collectively, we’d start blushing out of embarrassment if a report card on our upkeeping of the environment were to be worn as a lanyard. But blush not – the seaweeds are here!
Seaweed, as a third-generation biofuel feed- stock, could potentially circumvent many of the challenges posed by traditional fossil fuel alternatives, as it requires no arable land, fresh water, or fertilizer for cultivation and exhibits a higher biomass yield per unit area of cultivation than its terrestrial counterparts. Unlike lignocellulose, macroalgae have almost no lignin; therefore, their sugars can be released by easier and more economic operations. Seaweed cultivation could also directly improve the marine environment by removing CO2, heavy metal pol- lutants, and dissolved nutrients that would otherwise cause eutrophication.
This study conducted by Dr. Rofice Dickson and his colleagues evaluates the environmental impacts, economic potential, and makes a case of producing bioenergy from seaweed via biological conversion pathways, including the: sugar pathway; volatile fatty acids pathway; and methane pathway to produce ethanol, ethanol and heavier alcohols, and heat and power, respectively. Much like any other form of plant-based agriculture, seaweed production consists of two stages: cultivation and harvesting. Cultivation can be subdivided into four stages: the collection of fertile seaweed; spore release and sporophyte formation; rearing and nursing of seedlings; and offshore cultivation. The harvesting consists of activities related to the collection of seaweed from the sea and their transportation to a harbor.
The maximum seaweed price and minimum product selling price are both calculated as economic indicators. Overall, results demonstrate that the sugar platform is economically superior, as it provides a higher average maximum seaweed price of USD 121.6/t compared with USD 57.7/t and USD 24.2/t for volatile fatty acids platform and methane platform, respectively. However, the study also concluded that production via fermentation is so far the best alternative for energy production since it led to better economic and lifecycle outcomes.
A seaweed biorefinery could be located near a city close to the shore, which will provide necessary infrastructure and labor, such as Karachi. A seaweed cultivation site in Republic of Korea, with a distance of 15 km from the shore to the biorefinery, was considered for the analysis of terrestrial transportation. The main challenge in seaweed transportation is its high moisture content of 85–90 wt%. If the biorefinery is located far from cultivation sites, hauling wet biomass significantly increases transportation costs. Seaweed-based food companies utilize artificial drying to optimize the storage time. When being sold as a food product, the high seaweed price compensates for its high drying costs.
Although this study provides deep insight into the economic and environmental sustainability of green energy extracted from seaweed via biochemical pathways, some barriers to large-scale deployment of seaweed biorefineries, including high-quality biomass at a low price and adequate supply to meet the demands of industrial biorefineries, remain. In this regard, mechanized offshore cultivation and efficient seaweed farming techniques need to be developed to increase productivity and decrease the seaweed production cost.
Reference
P. Fasahati, R. Dickson, C.M. Saffron, H.C. Woo, J. Jay Liu,
Seaweeds as a sustainable source of bioenergy: Techno-economic and life cycle analyses of its biochemical conversion pathways, Renewable and Sustainable Energy Reviews, Volume 157, 2022, 112011, ISSN 1364-0321, https://doi.org/10.1016/j.rser.2021.112011
