Sheet 8: Using Sargassum for sustainable development

The importance of sustainable development

While warnings are resounding around the world about global warming and the massive destabilisation of all natural environments, it has become imperative to find new consumption solutions and reduce the pressure on natural resources. This requires the reuse of materials and better energy management. Global warming is one of the factors behind the multiplication of Sargassum and the “normalisation” of stranding phenomena, which are harmful from all points of view. However since 2011, many scientists have been looking into the question of how to make use of Sargassum, this green waste that we no longer know what to do with, from a sustainable development perspective.

One pollutant can clean up another

Research work is therefore multiplying to find solutions for the recovery of this extremely disabling Sargassum, harmful in every way. A major advance in Guadeloupe has been the result of many hours of analysis and experiments since 2018 by Professor Sarra Gaspard for the COVACHIM M2E laboratory at the Antilles University. Indeed, the Caribbean is facing two major risks linked to anthropic activities: mass strandings and the widespread pollution of soils by chlordecone- a chemical molecule that was widely used from the 1950s to the 1980s specifically for banana crops. This molecule is persistent and has been present throughout the food chain ever since (92% of French-Caribbean inhabitants have the molecule in their blood). It is therefore necessary to find a way of using algae as a bio-polluting resource.

Two processes have been developed by the professor and her team: Sargassum biochar (a soil improver made from biomass that increases yields), and Sargassum-activated Carbon (a material made up of carbonaceous material with a porous structure).

To obtain biochar, the Sargassum is carbonized for 3 hours at 700 degrees, without oxygen. For activated Carbon two techniques can be used:

Physical activation: made possible by two pyrolyses, the second in the presence of an oxidizing gas,
Chemical activation: the Sargassum is sprayed with a particular molecular solution to then undergo pyrolysis.

The results are very satisfactory insofar as the capture capacities of the polluting molecules are high, both on land and in water: 95% of the Chlordecone molecules are captured by the biochar and the activated Carbon. It can be noted that in contaminated soils, they degrade the chlordecone molecule in addition to storing it, i.e. the molecules lose their structure and all their Chlorine atoms. Biochar and activated Carbon are very interesting for agriculture, their porous structure also fixes Nitrogen and water, limiting soil erosion, and degrading more slowly than compost.

Tests in a giant oven called the “NST Solar Pyrolyser” (created in Guadeloupe and whose operating site is based in Morocco), 100% Carbon neutral and running on solar energy, could be agreed on during the Paris agreements on climate issues.

These furnaces (see photo) operate like microwaves, converting sun rays into energy and transforming biomass and green waste into high added-value Carbon products (Carbon powder, Biochar, activated Carbons, etc.) in four stages: granulation, solar pyrolysis, gasification and conditioning. This equipment has great potential when you consider that the most developed regions of the world spend a lot of money on management, storage and incineration of their waste without achieving any substantial value. In Guadeloupe, around 80,000 tons of Sargassum are washed up every year, and this solar oven alone could transform 27 tons of it every day into activated Carbon. Again, this is a Guadeloupean initiative, the final results of which are eagerly awaited, experiments are also taking place in Morocco.

Scientists from NBC (Bureau d’Étude Eau et Environnement based in Guyana, Haiti and the Dominican Republic) have developed a capacitive water deionisation cell, whose electrodes are based on activated Sargassum charcoal, in collaboration with scientists from Guadeloupe. The principle is as follows: place two electrodes in water, the negative ions will be attracted by the positive electrode and vice versa for the positive ions. These sargassum-based electrodes require very little electricity to operate. The potential is of unprecedented importance and one of the major challenges of our century since this operation can make water drinkable. Guadeloupe, the region that initiated this research, could be the first territory to patent this “sargassum charcoal-based” technique, which would bring drinking water to the most remote populations. It is a known fact today that 30% of the world’s population does not have access to blue gold, or potable water.

The methanisation process for Sargassum

Other recovery processes are being studied and are quite promising, especially with a shift to low-carbon energy. The methanisation of Sargassum to transform it into biofuels for example, could rapidly become a developing option, provided that Caribbean states invest in the industrialisation of this complex and expensive process. This process follows the pattern of the decomposition of Sargassum on beaches, fermenting with the lack of oxygen. The algae are first harvested and cleaned. The cleaning phase is extremely delicate, as sea salt can block the whole process, as well as sand. The algae are then dried and crushed and placed in the methanisers (large tanks deprived of oxygen) with a mixture of solutions that will prevent the presence of too much Hydrogen Sulphide. During this stage, micro-organisms will break down the algae and release methane.

Methanisation of Sargassum does require a certain standard of technical equipment, which is expensive. However the opportunities that this process offers are numerous, firstly because although Sargassum strandings are very irregular in quantity and timing, the seaweed can be mixed with other green waste from different agricultural sites (from grass to animal waste). Also, once produced, Methane can be injected into natural gas networks and used to produce heat or electricity. In Guadeloupe, Dominique Joly has been working on methanisation of Sargassum for several years

At the Centre for Scientific Investigations in Yucatán, Mexico (CICY), researchers in renewable energy are inoculating a fungus that can decompose algae and produce Methane. This micro-organism is all the more interesting as it is endemic to the region’s climate and exponentially favours Methane production: for one kilo of dry algae, 90 litres of Methane are obtained. There is even talk of growing Sargassum on the high seas, which can double its weight in as short as 18 days- an interesting fact when you consider that gas production requires a large quantity of green waste.

Methane is also the gas from which hydrogen is produced, another highly promising gas since it can potentially be used as a fuel for cars of tomorrow, as many studies underway throughout Europe and the US show. In Guadeloupe, Dominique Joly is working on the methanisation and hydrogenation of Sargassum and is collaborating with the French National Institute for Research on Agriculture, Food and the Environment (IRSTEA). The results regarding the quantity of gas produced by Sargassum are encouraging. The stakes are also high, since 95% of French hydrogen is derived from oil, and therefore carbon-based.

Methanisation of Sargassum can therefore be a real asset, particularly with regard to the green Hydrogen plan launched in September 2020 by the government, whose objective is to achieve Carbon neutrality by 2050. Hydrogen is an essential lever in the framework of energy transition. This must necessarily involve a series of massive investments in methanisation projects, particularly in Guadeloupe, the territory that initiated the process in the French Antilles.

Sources

Université Virtuelle de l’Environnement et du Développement Durable
guadeloupe.gouv.fr
Ministère de l’Agriculture
Université des Antilles
Trinidad and Tobago Government
Ecologie.gouv.fr

Préfecture de la Martinique
Global Voices
Feedelios (plateforme de financement participative des Outre-Mer)
www.larecherche.fr/environnement
France 24