Fishing for fertilisers in aquaculture waste
The land-based aquaculture sector is growing rapidly, generating large quantities of sludge and other types of biowaste. The team behind the Terraforming LIFE project are looking to create pathways to use this fish sludge in producing fertiliser, part of the wider goal of shifting towards a circular economy where resources are re-used, as Sigurður Trausti Karvelsson explains.
The aquaculture sector is growing rapidly in Iceland, in particular land-based aquaculture, which is expected to exceed the volumes of fish produced by the country’s sea-based farms within the next few years. This raises the question of how to deal with the increasing volumes of sludge generated at aquaculture facilities, in the form of accumulated fish faeces and uneaten feed. “Currently we lack the infrastructure in Iceland to receive that sludge and deal with it,” acknowledges Sigurður Trausti Karvelsson, a project manager at the Icelandic company First Water. This topic lies at the heart of the Terraforming LIFE project (https://terraforming.is/), in which researchers are both developing a new type of fertilisation plant to treat aquaculture waste, and also exploring new ways in which sludge can be used in the agriculture sector. “The goal in the project is to essentially create pathways to use this fish sludge. For example, it could be put through anaerobic digestion, and then used as a fertiliser in agriculture,” outlines Karvelsson, part of the team behind the project. “This would be a really good solution for fish farmers to dispose of their sludge.”
Sludge processing
This sludge typically includes nitrogen, phosphorus and certain heavy metals, yet potassium levels are usually low and salinity high, which makes it difficult to use directly in fertiliser production. The different parts of the sludge can be separated and processed however, generating products which can then be used in fertilisers and also in other areas of industry, representing a step towards a circular economy. “Putting the sludge and other biowaste like animal manure through an anaerobic digestion process results in a
process, which generates biogas and the digestate,” outlines Karvelsson. The project is focused primarily on salmon farming at this stage, and the composition of the sludge that is produced at these facilities will vary according to several different variables, an issue that Karvelsson and his colleagues in the project are also taking into account. “The nature of the sludge may vary depending on factors like the time of year, the average size of the fish being farmed, and temperature,” he explains. The long-term objective is to establish a pathway or plant capable of dealing with 100,000 tonnes of waste a year, one major stream of which will be fish waste, in line with expected growth in aquaculture. Two types of analysis have been conducted within the project, which will generate important insights in terms of the design of a plant. “We’ve performed chemical analysis in Iceland of different organic waste types to get a fuller picture of the amount of volatile solids, as well as the levels of nitrogen, phosphorus and other nutrients. A feasibility study has also been conducted in collaboration with a Danish engineering company, which will tell us more about the likely biogas yield and the properties of the digestate,” says Karvelsson. While the ability to produce biogas is desirable, Iceland is already rich in geothermal energy, so Karvelsson says the main priority is not renewable energy but rather producing fertiliser. “We aim to develop an operational plant capable of receiving large quantities of fish sludge, so there’s a pathway for aquaculture companies and salmon farmers in Iceland to dispose of their sludge. We want to have the authorities on board, with an effective regulatory framework in place,” he continues.
Circular economy
TERRAFORMING LIFE
From salmon sludge and manure to fertiliser: a circular economy around land- based salmon farming
Project Objectives
Terraforming LIFE aims to develop technologies and methods for a shared Integrated Agriculture-Aquaculture system that places farmers and aquaculturists at the center of a circular economy. By creating shared infrastructure and turning waste into value, the project addresses critical gaps in Iceland’s food supply chain and promotes sustainability in both agriculture and aquaculture.
Project Funding
This project has received funding from the European Union’s LIFE Programme under grant agreement No. 101113811.
Project Partners
• First Water
• Bændasamtök Íslands (Icelandic Farmers Association)
• Orkídea Innovation Promoter
• Ölfus Cluster
• SMJ Consulting Engineering
Contact Details
Project Coordinator, Sigurður Trausti Karvelsson First Water Urðarhvarf 8b
203 Kópavogur
Iceland T: +354 518 8000
E: sigurdur.trausti@firstwater.is W: https://terraforming.is/
Co-funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor the granting authority can be held responsible for them.
Sigurður Trausti Karvelsson
volatile solid fraction of the organic waste, which can then be used to produce biogas. This is mainly methane and carbon dioxide, but also some other types. The biogas can be burned to generate energy,” says Karvelsson. The nutritionally-rich parts are therefore more accessible, and can be combined with animal manure to produce fertilisers. “After the biogas has been taken out we’re then left with the digestate. Most of the nitrogen, phosphorus and potassium remains, which can be used in NPK fertiliser, which is very valuable for farmers,” continues Karvelsson. “In the Terraforming LIFE project we’re looking to optimise the processing of the sludge.”
A key aim is to develop methods to efficiently filter 80 percent of the total suspended solids from the effluent found in fish tanks, which will then be washed from drum filters into a specific channel heading to a de-watering station, designed to remove as much water as possible from the mixture. The ideal scenario is to reduce the salinity, while
“The goal in the project is to essentially create pathways to use this fish sludge. For example, it could be put through anaerobic digestion, and then used as a fertiliser in agriculture.”
at the same time maximising the amount of nutrients available for use in fertilisers. “For an engineer this is essentially an optimisation problem, whereas for a biologist it’s more of a research question. Ideally the sludge will contain between 15-20 percent dry matter, then it can undergo the anaerobic digestion
A reliable new pathway to get rid of sludge would be greatly welcomed by fish farmers, who currently need to filter it themselves before disposing of it. The project’s work opens up the possibility of not only disposing of fish sludge, but turning it into commercially valuable products, so establishing new revenue streams. “You’re not just getting rid of sludge, you’re actually making use of the fish faeces,” stresses Karvelsson. This also represents a significant step towards the wider goal of establishing a circular economy, where resources are re-used rather than simply disposed of, while at the same time helping Iceland reduce its dependence on expensive imports of fertiliser for its agriculture sector. “Organic fertiliser is already quite expensive in mainland Europe, then there is an additional transport cost to get it to Iceland. An organic fertiliser, produced locally from fish sludge and animal manure, would be a good, cost-
effective option for the agriculture sector as a whole,” says Karvelsson. The project’s research is primarily focused on salmon, yet the knowledge gained over the course of the project and the technology could be relevant to other aquaculture settings, with large amounts of fish sludge potentially available for processing. Organic fertiliser based on fish sludge and animal manure could be applied on different types of farms, while Karvelsson is also keen to highlight its potential wider impact in terms of the circular economy. “With this technology it would be possible to generate fertiliser from fish sludge and animal manure which would then go into agricultural settings. The fertiliser generated could also be used to grow the plant-based material that’s used for fish feed, subject to regulatory approval, with the necessary verifications and permits,” he outlines.
Sigurður Trausti Karvelsson is the Project Coordinator of Terraforming LIFE and also manages R&D projects at First Water. He has a Ph.D in biomedical science and specialises in research, data analytics, modelling, and innovation, with extensive experience in process modelling and optimization.
