Seaweed cultivation could provide a promising source of sustainable aviation biofuels, finds Norwegian report
SINTEF Fisheries & Aquaculture received $2.8m funding from the Norwegian Research Council to establish an interdisciplinary knowledge platform for industrial cultivation of seaweed.
Tue 28 Mar 2017 – Seaweed could become a promising source of biofuels for aviation if sustainably produced and economic and policy challenges can be overcome, says a report by Norwegian NGO Bellona. Seaweeds, or macroalgae, generally contain high amounts of carbohydrates (sugars) that make them highly suitable for bioethanol and biobutanol production, where the sugars are fermented. They belong to the fastest growing species in the world and growth rates far exceed those of terrestrial plants, plus the rapid growth also means they absorb significant amounts of CO2. Most importantly, they do not compete for valuable land space or fresh water during cultivation as do many crops grown for biofuels. Industrial seaweed cultivation, where it is mainly used in food production and pharmaceuticals, is largely confined to Asia whereas in Europe it is in the very early development phase. However, says the report, there is a golden opportunity to design a high-potential sustainable aviation biofuel industry effectively from scratch.
This is especially the case in Norway, whose coastline stretches 21,000km, equivalent to 2.5 times around the equator, and encompassing an area of 9 million hectares. The temperate waters that stretch from Portugal to Norway are also highly suited to certain species of brown kelp seaweed, in particular sugar kelp.
“Seaweeds are a large and diverse group of plants, some of which, like sugar kelp, could be a promising source of ocean-based biofuels,” said the author of the report, Marika Andersen. “Any potential use naturally depends on sustainable management, a better understanding of local environmental impacts and the life cycle emissions. But climate science is clear that we need to consider all alternatives to fossil fuels, and Bellona believes seaweed may be an untapped option.”
With a water content of 85-90%, seaweeds are particularly suitable for wet fuel conversion methods such as anaerobic digestion and fermentation. The carbohydrates are mainly glucose, galactose and mannitol. The low lignin content of seaweed eliminates many of the challenges faced by wood-based bioethanol producers, as lignin hardens the cell walls and requires pre-treatment before fermentation. Also, as compared to forest/woody biomass, seaweeds’ higher growth rate means there is a higher turnover rate and they could theoretically be cultivated inexhaustibly.
Giant kelp grows faster than bamboo at about 7-14cm per day – even up to half a metre under ideal conditions – with sugar kelp grown in UK waters being shown to grow 1.1cm per day, equivalent to reaching over 2.25m in a year. Average productivity of wild seaweed ranges between 3-11kg/sqm dry weight (dried seaweed retains about 10-30% of the original wet seaweed’s weight) and up to 13kg/sqm for cultivated seaweed per year. For comparison, one of land’s most productive crops, sugar cane, reaches yields between 6-9.5kg/sqm wet weight per year.
One hectare of seaweed can fix about 66t of CO2 from the atmosphere. Depending on the species, it will take between 10-100 years before the CO2 in a combusted tree is recaptured in regrowth. For seaweed, taking about six months to mature, it absorbs CO2 at a much quicker rate and the carbon released from its combustion is thereby sooner reabsorbed.
Furthermore, seaweed is incredibly efficient at taking up nutrients such as nitrogen and increasingly scarce phosphorus, which it absorbs with comparable efficiency to a waste-water treatment plant. This eliminates the need for fertilisation and, in fact, cultivation of seaweeds in practice means recapturing nutrients into biomass that in turn can be reused for fertilisation purposes. When cultivation is located in proximity to fish farms, seaweed can use the excess, otherwise wasted, nutrients and thereby ensure recycling and cleaning of the surrounding waters.
Despite the many positives that marine biofuel feedstocks can bring to overcome the sustainability issues faced by land-based biomass, the report says that more research is required to improve understanding of the consequences of embarking on industrial-scale marine biomass production. There is also a lacking of research into the potential life-cycle assessment of seaweed biofuel emissions, and the report recommends studies should be undertaken based on real-world pilot and eventually large scale seaweed-for-energy cultivation. However, integrated seawater production is important, it adds, for example by sharing offshore infrastructure like wind farms and fish farms.
About half of the sugars in seaweed are locked in a single carbohydrate – alginate – which is currently one of the biggest drivers of the seaweed industry and is widely used in the food sector where it is applied as a stabiliser or an emulsifier, for example in dairy products like ice cream. The main producers are in Scotland, Norway, China and the USA, with smaller amounts being produced in Japan, Chile and France.
In spite of the huge market requirement from industries like aviation for biofuels, the report notes seaweed biofuel production is today the product with the lowest earning potential for seaweed production, a common obstacle the sector faces. Typical prices for seaweed reach up to €1,000 per kg for bioactives in the pharmaceutical industry.
“The goal must therefore be to implement incentives, reduce costs and to increase the profitability of seaweed production for energy purposes,” said Andersen. “Because the other uses of seaweed garner such high value, overcoming the fragmentation of the seaweed value chain by establishing an advanced biorefining industry can help achieve this.”
Dealing with the challenges in the production phase holds the potential to dramatically improve cost profiles, she says. However, there are other challenges, not least the perception that the seaweed cultivation industry is low-tech and fails to attract the human and capital investment that would drive down costs.
Bringing seaweed biofuels to market will require concerted effort along the entire value chain, demanding more strategic collaboration between the involved sectors, says the report, adding the aviation industry must also invest in the capacity to produce and use such fuels.
Addressing European policymakers, the report says they must develop long-term market conditions and implement incentives, at least until 2030, that provide predictability of risk to those who invest in the seaweed cultivation business. Earlier generations of biofuels should be phased out and curbed, and with no other decarbonisation options, the aviation sector must receive priority for the limited sustainable biofuels available, it concludes.
“If sustainably produced and used, seaweed could be an available, scalable and productive energy resource,” commented Andersen. “This report calls on policymakers to consider seaweed as an alternative to fossil fuels, especially for sectors like aviation that can’t readily switch to batteries.”
The study was funded by a grant from Norwegian state-owned airport operator and air navigation service provider Avinor. By 2030, Avinor has targeted that 30% of all jet fuel sold in Norway should be sustainable alternative fuel, which will require 350-400 million litres of jet biofuel annually.
“We are totally dependent on aviation in Norway. Avinor’s clear goal is to be a driving force in the work on climate and environmental challenges within our industry. This includes a significant engagement in developing and phasing in sustainable alternative fuels in the aviation industry,” said Olav Mosvold Larsen, Senior Advisor at Avinor. “I think this report is very interesting and illustrates the potential of utilising marine resources for aviation fuel in the future.”