Aerial view of a sargassum mat stranded along a Caribbean coastline, with clear turquoise water on one side and dense mangrove forest on the other

Sargassum biorefinery · Geneva · Caribbean · French Guiana

Turning a pollution into a resource.

A cascade biorefinery for stranded Caribbean and Atlantic sargassum.

Revalena is developing a cascade biorefinery that cleans up stranded sargassum: it captures the arsenic and heavy metals the seaweed concentrates, recovers its valuable molecules and turns the residue into renewable energy.

The project

A recurring environmental burden, with no industrial treatment route

Since 2011, massive sargassum strandings have affected coastlines across the Caribbean and the tropical Atlantic. They damage coastal ecosystems and tourism, disrupt fishing and navigation, and expose coastal populations to hydrogen sulphide released as the seaweed decomposes.

Today, public money is spent clearing beaches and landfilling the biomass, where it keeps emitting methane and hydrogen sulphide uncontrolled, and where the arsenic it carries can leach into soils and water. Revalena treats this material as a resource: recover its valuable molecules first, then convert the residue into renewable gas, while locking the contaminants into a solid mineral fraction.

Thick mat of stranded sargassum seaweed covering a white-sand Caribbean beach at the waterline, with anchored boats offshore

Now let's understand how it works.

The cascade biorefinery

Extract, depollute, convert

Gasification is only one stage of a wider process. Before reaching the reactor, the biomass is pretreated to remove most of its contaminants, then passes through a cascade extraction of high-value molecules, recovered while they are still intact.

arsenic in sargassum leachate vs. the EU drinking-water limit: ≈ 1,100×; arsenic in sargassum leachate vs. the EU drinking-water limit; MeasuredSource: Revalena analysis, 2025
wash, extract, gasify, contain: 4 steps; wash, extract, gasify, contain
Dominican Republic & French Guiana: 2 axes; Dominican Republic & French Guiana

Stage 1
Pretreatment
Washing removes most of the chlorine and a large share of the arsenic, which makes the biomass safe to process further. The washing water is collected and treated.
Demonstrated
Stage 2
Cascade extraction
High-value molecules are extracted while still intact, before the residual biomass reaches the reactor. This work is developed under the SARGASOL programme with the Grand Port Maritime de Guyane. No compound has been selected yet: the choice will depend on yields, purity and profitability.
Under study
Stage 3
Hydrothermal gasification
The extraction residue is converted in supercritical water, a route suited to wet biomass that needs no drying step. Gasification tests on real sargassum were carried out on CADE's pilot platform in Spain.
Demonstrated
Stage 4
Outputs
A renewable gas, a solid mineral fraction that concentrates the arsenic, and a liquid effluent treated before discharge. The gas can be upgraded to renewable methane; other routes such as methanol remain possible.
Demonstrated

Pilot tests carried out with CADE Soluciones de Ingeniería (Spain).

The technology

CADE's supercritical water gasification

Above its critical point (374 °C and 221 bar), water becomes a reactive medium that converts wet organic matter into a renewable gas, while mineral salts separate out. CADE operates pilot and demonstration units in Spain.

Source: Supercritical water gasification technology · CADE Soluciones de Ingeniería, Sep 2026

CADE supercritical water gasification equipment, an open teal-coloured unit housing the reactor and piping

CADE supercritical water gasification equipment, supplied by Revalena

Cascade extraction

High-value molecules under study

Carotenoids and sterols
Cosmetic and nutraceutical uses
Under study
Polysaccharides
Health, nutraceutical and industrial uses
Under study
Polyphenols
Antioxidants for cosmetic and nutraceutical uses
Under study
Biostimulants
Agricultural uses
Under study

No molecule has been selected at this stage: the final choice will depend on extraction yields, achievable purity and profitability, which remain to be established. Arsenic is treated, not valorised.

Environment & health

Arsenic and heavy metals are captured, not displaced

Sargassum concentrates arsenic and other heavy metals from seawater. Our process was chosen precisely because it handles these contaminants inside the installation and concentrates them into a small, containable solid stream, instead of shifting them to soils, landfills or the sea.

Where the arsenic goes

Washing removes a large share upstream
The washing water that carries it is collected and treated.
Gasification concentrates most of the rest in the mineral salts
The arsenic leaves the process in a small, solid, containable stream.
The liquid effluent is treated before discharge.

Why it matters

≈ 1,100×

arsenic in sargassum leachate vs. the EU/WHO drinking-water limit

Leachate from decomposing sargassum carries arsenic into soils and coastal waters. In our analyses, it contained about 1,100 times the EU and WHO drinking-water limit for arsenic. Published field studies show that 50 to 90% of the arsenic in stranded sargassum is released as it decomposes. To our knowledge, no value chain to date combines valorisation, depollution and energy.

Source: Revalena analysis · Revalena Sàrl, 2025

Source: Chávez-Vergara et al., 2022 · Environmental Science and Pollution Research 29: 91071–91080, 2022

Source: Olguín-Maciel et al., 2025 · Aquatic Botany 199: 103884, 2025

Divert
Out of landfills
Stranded sargassum is diverted from open-air decomposition and landfill, where it emits methane and hydrogen sulphide uncontrolled.
Depollute
Contaminants contained
Arsenic, heavy metals, chlorides and sulphur are handled inside the process rather than left as an external liability.
Substitute
Renewable gas
A renewable gas that can replace imported fossil natural gas and could add dispatchable renewable capacity to island grids.
Close the loop
Toward zero waste
Valuable molecules first, energy next, minerals concentrated for safe handling, and effluent treated before discharge.

UN Sustainable Development Goals

Life below water
Reducing the burden of sargassum drift on coastal and marine ecosystems.
Climate action
Avoiding uncontrolled methane emissions and substituting fossil gas.
Responsible consumption and production
A circular valorisation of a biomass treated today as waste, toward zero waste.
Affordable and clean energy
Renewable gas produced from a local, recurring resource.
Industry, innovation and infrastructure
A new industrial route combining extraction and hydrothermal gasification.
Partnerships for the goals
An international consortium across Europe and the Caribbean.

Our vision

A modular biorefinery, deployable close to the resource

In the long term, we aim for a modular, transportable installation, built by replicating identical units, to treat sargassum where it strands. The next step is scaling up to demonstration size, in preparation with our partners.

Vision

Long-term vision — not yet demonstrated.

01
Valorise: high-value molecules first, energy next
02
Depollute: arsenic and heavy metals concentrated in a solid mineral fraction
03
Decarbonise: renewable gas in place of imported fossil gas

Diagram of the sargassum cascade biorefinery: pretreatment, cascade extraction, hydrothermal gasification, and outputs (renewable gas, high-value compounds, treated water, mineral salts)

Principle diagram of the sargassum cascade biorefinery, supplied by Revalena

Our values

What guides our work

Ecology
Protect coasts and oceans
Our starting point is an environmental emergency: removing a recurring pollution from Caribbean and Atlantic shorelines.
Health & safety
Treat the risk, never shift it
Arsenic, heavy metals, chlorides and sulphur are handled inside the process and concentrated into a small, containable solid stream.
Circularity
Toward zero waste
An integral valorisation of the biomass: valuable molecules first, energy next, effluent treated before discharge.
Rigour
Measure, don't assume
Every maturity step is tied to documented work. We always distinguish what is established from what remains to be demonstrated.
Transparency
Name our risks
A project that models its own accident scenarios and states its residual weaknesses is more robust than one that simply asserts safety.
Cooperation
Local roots, shared expertise
Switzerland, Spain, France, French Guiana, the Dominican Republic and Martinique: science, engineering and field knowledge, with local teams trained on site.

Timeline

Two axes, one programme

Our research programme runs in parallel on two axes, each with its own partners and public funding.

Axis 1 · Caribbean

Dominican Republic

Feedstock characterisation, pilot gasification tests and risk assessments. Funded by the Inter-American Development Bank since May 2025, now in its closing phase.

Axis 2 · Atlantic

French Guiana: SARGASOL

Integral valorisation covering cascade extraction and the energy route. The third phase, SARGASOL (2026–2028), is under way within an ADEME and ANR programme.

What has been completed

Aug 2024
Research agreement between Algaltek and the Grand Port Maritime de Guyane: start of phase 1
Axis 2 · Atlantic
May 2025
Start of the IDB project
Axis 1 · Caribbean
Nov 2025
ADEME agreement
Axis 2 · Atlantic
2026
Pilot gasification tests with CADE
Axis 1 · Caribbean

In progress

Oct 2026
Tripartite agreement
Programme
2026–2028
SARGASOL programme under way; IDB final report
Programme

Next step

Scaling up from the pilot platform to demonstration size, in preparation with our technology and scientific partners.

Partners

An international consortium

Revalena Sàrl, a Swiss company based in Geneva, leads the programme. The Grand Port Maritime de Guyane is our historic partner; CADE is our main technology partner.

Grand Port Maritime de Guyane
Historic partner · French Guiana
Official partner that financed a large part of the programme's early development. Sargassum collection logistics and support in port relations. Holder of the SARGASOL agreement.
CADE Soluciones de Ingeniería
Main technology partner · Albacete, Spain
Supercritical hydrothermal gasification technology. Feedstock characterisation and gasification runs on sargassum at its Albacete pilot platform.
INTEC
Scientific direction · Santo Domingo, Dominican Republic
Scientific lead of the Dominican axis: analyses, risk and environmental assessment.

Sargawatt
Sourcing · Martinique
Algaltek SA
Research · Saint-Aubin (Fribourg), Switzerland
Laudato Sea
Laudato Sea
Strategic & maritime advisory
Alcantara Industries
Alcantara Industries
Industrial engineering
Finance for Impact
Techno-economic modelling
Assertive Group SA
Ethical negotiation · Geneva, Switzerland

Scientific, local and institutional partners

EPFL
UNEV
SOGEMA · Serd

With the support of

Where it began.

Algaltek SA, an EPFL spin-off, established the science and proof of concept for sargassum valorisation, validated in the Dominican Republic with the IDB. Algaltek then entrusted the industrial development of the biorefinery to Revalena, a company created specifically for this purpose, in continuity with its scientific team.

Contact

Let's talk about your coastline

Local authorities, ports, industrial partners, investors or research teams: we would be glad to hear from you.

Management: Sonia Grimm, CEO
Email: sonia.grimm@revalena.ch
Phone: +41 79 830 48 71
Address: Revalena Sàrl
Rue de la Rôtisserie 8
1204 Geneva, Switzerland