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Green seaweeds clean up in Queensland

Updated: Dec 20, 2022

A green Ulva species, or sea lettuce, is grown by Pacific Bio at its Queensland prawn farm. Photo: Pacific Bio

Two companies are leading the production of farmed seaweed in Australia, growing green species to help remove nutrients from prawn farms in Queensland.

The companies Pacific Bio Technologies and Tassal Group have both been involved in seaweed production for several years. Both are members of the Australian Sustainable Seaweed Alliance, which has outlined achievements by the two companies in its annual report on its members' progress released in October.

The report says Australia’s largest aquaculture company, the Tassal Group, harvested 2500 tonnes of green seaweed in 2021-22, which makes it the country's largest producer of seaweed. The seaweed was grown in the water filtration ponds on its prawn farm at Proserpine in Queensland.

Refocused on bioremediation

For the past 6 years, Tassal has been exploring seaweed production at sea in conjunction with its Atlantic Salmon operations in Tasmania. But the company launched a new trial in 2021 in conjunction with its prawn farming operations.

Head of Engineering and Risk Management at Tassal Justin O’Connor says, the company is now actively developing seaweeds as a bio-remedy to further enhance the treatment of water on its prawn farms. The Queensland trial is part of a $1 million, two-year project funded through the Fisheries Research and Development Corporation, with the University of the Sunshine Coast as the lead research provider.

O’Connor says three green seaweeds – Cladophora, Chaetomorpha and Ulva – were found growing on the prawn farm and have been used for the trials. Seedstock was collected from along the water networks and channels across the farm. This seaweed had effectively self-propagated, after being brought onto the farm with the estuarine water it draws from the Gregory River for the prawns.

The seaweed has been grown in seven of the company’s 12 settlement ponds at the Proserpine farm and provides a natural opportunity to improve water quality and, at the same time, produce a second commercial crop on the farm.

Water settlement ponds on the Tassal prawn farm at Proserpine, Queensland are being used for the production of green seaweed. Photo: Tassal Group

It is continuously harvested by trimming with a pond harvester, a process O’Connor describes as “much like mowing the lawn, but under water”.

Early trial results show that the seaweed has doubled the effectiveness of the nutrient removal process in the settlement ponds, further improving the quality of water before it is discharged into the local estuary. The seaweed actively draws nutrients out of the water in order to grow.

The seaweed itself also offers a potential new product for the business. “Seaweed has multiple uses and we are exploring the best use of it with multiple third parties,” O’Connor says. “We are also considering what other species we can trial, including Asparagopsis, which, when fed to cattle, can significantly reduce their methane emissions.”

He says other prospective uses include compost and fertiliser, stock and aquafeeds, and biochar for carbon sequestration. There are also more advanced bioplastics, food and biotech applications.

“It’s early days for us. We plan to start with something simple and develop from there.

"What we can say so far is that we’ve successfully grown a lot of seaweed, and it has done a great job of even further improving our water quality.” Justin O'Connor, Tassal Group

Tassal is well positioned to produce seaweed, with infrastructure already in place for prawn farming. The 287ha Proserpine farm will be the focus of the company’s seaweed activity. It also has smaller prawn farms of 32ha at Mission Beach, Queensland and 45ha at Yamba, NSW, where seaweed farming can also be trialled.

In the coming year, the research project will consider other species that could be grown in the ponds, and the farm practices required for more consistent growth rates.

“When conditions are good, the seaweed can double its biomass in a week,” O'Connor explains. "At other times it remains virtually dormant. We want to devote further study to the conditions that are driving these volatile growth patterns. Fortunately, the seaweed team we work with at the University of the Sunshine Coast is a strong partner in the project and will help with this work.

“Our ponds and pumping systems provide us with the ideal opportunity to provide seaweed with the water quality conditions that best suit its growth. For this reason, the focus of our seaweed farming is in Queensland, where both the growth rates and the commercial opportunities are strongest.”

Zero net discharge

Also growing seaweed in conjunction with prawn farming in Queensland is Pacific Bio, which bills itself as an aquaculture and technology firm. It has used a species of Ulva to remove nutrients from water on the company’s prawn farm at Ayr, south of Townsville, since 2018 and has also developed a system using green algae to remove nutrients from freshwater and urban sewage.

In 2021-22, its RegenAqua™ macroalgal bioremediation system on the prawn farm produced 1000 wet tonnes of seaweed, along with 1000 tonnes of prawns.

“We are continuing to develop that technology and have built world-class seaweed nurseries at our Alva Beach algal facility next to our prawn farm," says Pacific Bio CEO and Managing Director Sam Bastounas.

"We are working towards a zero net discharge farm – zero carbon, phosphorus, and nitrogen." Sam Bastounas, Pacific Bio

"Our vision is to enable the growth of sustainable onshore aquaculture in Australia and around the world using green seaweed.

“We’re rapidly trying to build capacity in our networks, and we are open to commercially supplying seaweed from our nursery. We have had several aquaculture businesses approach us – ­barramundi and prawn farmers. They all have the same water treatment issues,” Bastounas explains.

Demand for the company’s seaweed and algae products currently exceeds its ability to supply and the company is actively raising equity to continue its rapid expansion. Its products include PlantJuice™ (a biostimulant for the agricultural sector) and ReefAsta™ (a wellness product developed by the company), as well as aquafeeds and a range of animal feeds.

Pacific Bio's water treatment and seaweed production system. Photo: Pacific Bio

Urban water treatment

As well as working with the aquaculture sector, Pacific Bio uses another form of green algae in urban water treatment and has recently consolidated plans to expand the use of its RegenAqua technology in conjunction with local councils in Queensland and Sydney.

Results from a RegenAqua pre-facility operating in conjunction with the Burdekin urban wastewater plant since March 2021 have exceeded world's best practice for reducing nutrient pollution. Construction of a commercial-scale demonstration facility is expected to begin within the next 12 months, supported by Burdekin Shire and state government funding.

Planning is underway for further RegenAqua projects with Townsville City Council, at Magnetic Island and Hinchinbrook. Pacific Bio is also building a RegenAqua pre-facility at Sydney Water's Picton water treatment facility, expected to be fully operational by January 2023.

In addition to the promising results in water treatment, Bastounas says algal bioremediation offers comparable results but is substantially cheaper than traditional treatments such as membrane reactors, which are both expensive to build and power-hungry to run.

“The beauty of our system is its circularity, in that we extract nitrogen and phosphorous out of the waste stream and make biostimulants that are critical inputs for farming,” says Bastounas. He notes that capturing phosphorus is particularly valuable; it is an essential input for healthy crops, but globally it is a limited resource and dwindling supplies.

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