Ocean Pollution

Researchers convert washed-up seaweed into biofuels and fertiliser

written by Oceanographic Staff

Every year, millions of tonnes of seaweed washes up on beaches of Mexico, the Caribbean and many others around the world.

But UK researchers from the Universities of Exeter and Bath have developed a financially viable and simple way of pre-processing seaweed before making bulk chemicals and biofuels from it. This process will also remove plastic from the oceans and help to clean up tourist beaches in the Caribbean and Central America.

The aim is to use invasive seaweed such as Sargassum – an environmental nuisance which currently costs the tourist industry vast sums, both in clean-up costs and because it deters visitors.

“Many countries in the Caribbean and Central America rely heavily on tourism, so the coronavirus pandemic and the ongoing Sargassum problem have put them on their knees,” said Professor Mike Allen, of the University of Exeter and Plymouth Marine Laboratory. “Last month more than 4 million tonnes of problematic seaweed washed up on their shores.”

seaweed biofuels

Partly fuelled by fertilisers washing into the sea from farming in the Americas, the foul-smelling Sargassum seaweed devastates the tourism industry and harms fisheries and ocean ecosystems.

This is the latest in a string of developments around seaweed processing from the team, which is supported by UKRI, Global Challenges Research Fund, Roddenberry Foundation, Innovate UK and Newton Fund.

“Ultimately, for this to work it has to make financial sense,” said Professor Allen. “Processing marine biomass like seaweed usually requires removing it from the salt water, washing it in fresh water and drying it. The costs of these processes can be prohibitively high. We needed to find a process that would pay for and sustain itself – something both economically and environmentally viable. This work provides a crucial missing step towards a true salt-based Marine Biorefinery by establishing the initial fractionation step.”

Using acidic and basic catalysts, the research team devised a process that releases sugars that can be used to feed a yeast that produces a palm oil substitute. This method also prepares the residual seaweed for the next processing stage – hydrothermal liquefaction.

This process put the organic material under a high temperature and pressure, turning the seaweed into bio-oil that can be processed further into fuels, and high-quality, low-cost fertiliser.

“In contrast with existing pre-treatment strategies, we show that an entirely salt-based biochemical conversion route can work,” said Ed Jones, first author on the paper and PhD student at the Centre for Sustainable Circular Technologies at the University of Bath. “For the first time this study demonstrates that, rather than a hindrance, the presence of saltwater can be helpful.”

The benefits of this project are two-fold. Inspired by Professor Allen’s children, who helped collect seaweed samples for trial studies from the Devon coast, the team have ensured that any plastic collected with the seaweed will also be converted.

“The oil industry creates a variety of products including liquid fuel, plastics and fertilisers – and we can benefit from a similar flexibility,” said project lead Professor Christopher Chuck, Director of the Centre for Integrated Bioprocessing Research at the University of Bath. “We can simply alter the process conditions to produce larger or smaller amounts of specific by-products, allowing us to have meet variable demand.”

The researchers are now seeking to develop seaweed based biorefineries to provide local solutions and opportunities on the global stage.

Stock photo courtesy of Wolfgang Hasselmann.

To read the full paper, “Saltwater based fractionation and valorisation of macroalgae”, click here.

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