Everything has value
One person’s waste could be another’s valuable commodity, as the aquaculture sector is discovering.
The “circular economy” is one of those buzzwords that, like “sustainability”, can be stretched to make a point.
In essence, though, the concept can be defined as an economic system aimed at eliminating waste and making better use of resources.
It is usually contrasted with the traditional “linear economy” which follows a “take-make-dispose” model which has become the norm ever since the dawn of the Industrial Revolution. The linear economy not only uses up natural resources unsustainably – it also creates waste which needs to be disposed of somehow.
How by-products can be used
In the context of aquaculture, there are two key themes to a circular approach: first, ensuring that as much as possible of any fish that is farmed or caught is used to create value; and secondly, dealing with waste by-products such as fish farm sludge as potentially valuable “co-products”.
A report commissioned in 2022 for the European Union’s iFISHiENCi initiative recommended approaches such as improving the circularity of feeding (such as growing algae fed on nutrients from aquaculture waste), or valorising fish waste from land-based fish farms.
When it comes to minimising waste in fish processing, the undoubted leader right now is Iceland. The 100% Fish initiative championed by the Iceland Ocean Cluster, in particular focused in Atlantic cod, is one that other seafood nations have been looking at with great interest.
Adding value to the cod catch through by-products
The cluster will be hosting a conference with the theme of “Fish Waste for Profit” on 19-20 September, but as a taster, it held a webinar moderated by the organisation’s CEO Alexandra Leeper.
The webinar featured: Dr Thor Sigfusson, Founder and Chairman of the cluster; David Naftzger, Executive Director, St Lawrence Governors and Premiers, Great Lakes, representing fisheries in US/Canadian Great Lakes region; Petra Weigl, Managing Director, Europe, with tilapia farmer Regal Springs; and Ben Wiper, Founder and CEO, 3F Waste Recovery.
As Alexandra Leeper pointed out, an incredible 10 million tonnes of the world’s target catch is wasted every year. Seafood businesses are typically focused on fillets as the product consumers know, understand and want to see on their supermarket shelves.
But there is so much more. The 100% fish initiative has encouraged Iceland processors to use fish by-products for applications such as nutraceuticals, cosmetics and even skin grafts created from cod skin.
Salmon in fish processing plant
Dr Sigfusson gave two recent examples: a hand cream based on lobster chitin, and “leather” goods made from whitefish skin.
He said: “There is real value to be had from product that is lying around in dumpsters around the world.”
David Naftzger said that in the Great Lakes, the fisheries’ catch previously went to fillets and low-value animal feed; now, applications are being developed to create collagen, hydrolysate and fish leather.
He said: “We estimated that we could double or triple the return on caught fish.”
On the farming front, Regal Springs aims for a zero-waste policy with the intention that no part of its tilapia will end up in landfill. As Petra Weigl explained, the company is already 95% of the way there. The only element not currently being used is the blood.
Regal Springs set up a new division, Natural Additives, to find more high-value uses for fish. As Petra Weigl put it: “We should all feel morally obliged to use 100% of the fish we catch or farm.”
Rotating drum filter for water filtration in a fish farm
She stressed however that “every fish is different” and a company’s ability to achieve “100% fish” depends on its size, local infrastructure and ability to invest. Regal Springs typically operates in remote rural areas, in countries like Indonesia, with little local infrastructure – in stark contrast to Iceland.
What’s possible also depends on the properties of a producer’s fish. For example, salmon, especially if has had a diet with a large element of marine ingredients, will tend to be high in omega-3 and the fish oil derived from it will be high value. In contrast, a freshwater fish like tilapia, that can thrive on a plant-based diet, will produce fish oil that is less premium.
As Ben Wiper explained, learning how to use by-products is a game-changer for fisheries, changing the dynamic from “biggest quota wins” to “best technology wins.”
3F was set up to develop useful products from fish heads, skin and bones – the elements that end up in landfill or at best, animal feed. As Wiper explained, the “crown jewel” is its range of collagen products, including the world’s first 99.5% pure medical-grade collagen, which can be used for artificial skin grafts, tissues and organs.
Its business model is to work with seafood companies, licensing its technology, building biorefineries and creating a ready market for the processed product.
Wiper, who believes this kind of technology will change the industry fundamentally, predicted: “In the next 10 years, we will see a cosmetic or pharmaceutical company acquire a fish processing company.”
A circular approach to feed
One of the criticisms levelled at the aquaculture sector is that aquafeed is too dependent on catching wild fish from the world’s diminishing fish stocks. A more sustainable solution could be to use the nutrients in aquaculture waste – basically “sludge”, a mix of fish faeces and uneaten feed – to grow plants and animals that fish can eat.
As Fish Farmer reported last November (“Worms can help find value in fish farm waste”, November 2023), researchers at the Scottish Association for Marine Science (SAMS), with funding support from the Sustainable Aquaculture Innovation Centre (SAIC), have been working on a process to extract solid nutrients from sludge, so that it can be fed to polychaetes, marine worms that can be used as the basis for shrimp or animal feed.
The ongoing project involves first an electrochemical process and ultrasound technology which extracts excess water from waste matter, and secondly a trial to assess the nutritional value of polychaetes fed in this way.
Georgina Robinson with polychaete worm
Dr Georgina Robinson, lead researcher and UKRI Future Leaders Fellow at SAMS, said at the time: “Aquaculture waste is not typically considered as valuable as co-products from other sectors, but there are a range of opportunities to be explored that could change that attitude. By taking a circular approach, we can use the co-products to aid the growth of other organisms that will, in turn, benefit the sector as a sustainable feed ingredient.
“This is the first time the water treatment system has been used for freshwater waste and the results of the project could show huge potential for it to be adopted more widely.”
Biochar
Where there’s muck…
Raising polychaetes is just one of the potential ways to valorise fish farm sludge. Other uses include:
• Composting: sludge can be composted to create nutrient-rich organic fertiliser. Mixed with organic materials like sawdust, straw or wood chips it can be used as compost.
• Anaerobic digestion: the sludge is broken down in an oxygen-free environment, creating biogas (a mix of methane and carbon dioxide) and digestate (a nutrient-rich by-product). Biogas is a renewable energy source while the digestate can be used as fertiliser.
• Biochar: Fish farm sludge can be converted to biochar through pyrolysis (thermal decomposition in the absence of oxygen). Biochar is a stable form of carbon that can be used to enrich soil.
• Land application: properly treated, fish farm sludge can be used directly on agricultural land as a fertiliser or soil conditioner.
• Aquaponics: fish farm sludge and/or wastewater can be used to fertilise plants grown in an aquaponic facility (combining hydroponic agriculture with aquaculture).The plants in turn help to purify the water which can then be recirculated back into the fish tanks.
• Worm farming: fish farm sludge can be fed to earthworms, which convert it into high-quality “vermicompost”.
There are a couple of caveats, however. First, when using sludge as a source of nutrients, it is important not to apply an excessive amount, which could lead to eutrophication – an explosion in harmful algae growth – in rivers, lakes and coastal waters.
Secondly, collecting sludge is only practical for land-based fish farms and hatcheries, or (in theory at least) closed or semi-closed pens at sea. In conventional net-pen farming, fish faeces and uneaten feed pellets are either dispersed by tides and currents or drift to the seabed under the pen.
Also, it is crucial to have a reliable, cost-effective process that can separate out solids and liquids and turn the solid element into something that can be transported and used.
Denmark-based Alumichem, for example, has a four-stage process to help its RAS (recirculating aquaculture systems) fish farming customers deal with waste. First, the sludge goes through a thickening step to takes the dry matter content from 0-1% and up to 10% solids, and significantly reducing the sludge amount. This involves chemical conditioning of the sludge to build large flocs (loosely clumped masses of fine particles), followed by mechanical filtration to separate these floc particles from water.
After thickening, the sludge is ideal for biogas production, but it can also go through a further dewatering step, in which the dry matter content can reach 30% solids. The dewatered sludge can be further treated in a sludge dryer to achieve more than 90% solids. Finally, any excess water separated out as part of the process is “polished”, removing any remaining elements such as solids, nitrogen or heavy metals.
Trevor Gent, Director of Engineered Solutions with Alumichem, said: “We always focus on the overall process from both a CAPEX and OPEX perspective.
“For example, if biogas facilities are nearby then we would look at providing the highest dry matter possible to maintain ‘pumpability’ of the sludge. This reduces transportation costs for the fish farmer while ensuring a transportable product to the biogas facility.
“Where biogas isn’t the primary availability we work with the fish farmer to solve the sludge problem to ensure that the sludge is transported to a circular economy opportunity: fertiliser, soil amendment, etc.”
He added: “The main approach is to ensure that there is no cross contamination of the waste and ensuring the sludge contains the highest level of available phosphorous and nitrogen as these are the two highest value components available in fish sludge. This is done by removing the sludge first before performing any denitrification steps. This ensures that the phosphorous is precipitated and the insoluble nitrogen is collected in the sludge and available for the next user.”
Bakkafrost’s Førka biogas plant
It’s a gas
Another example is Bakkafrost’s biogas plant at Førka in the Faroe Islands. This not only converts waste from the salmon farmer’s land-based facilities into renewable energy in the form of heat and electricity, but also takes in food waste from local authorities, hotels and wholesalers in the area, and manure from dairy farmers. The plant also produces solid waste for fertiliser.
Førka produced 11,404 Mwh of energy in 2023, although compared to the previous year that represents a reduction of 25%.
Blue Ocean Technology container
Aquaculture waste is becoming a commodity with value in its own right, as can be seen with the decision by Norwegian fish processing heavyweight Pelagia to take a 100% stake in Blue Ocean Technology (BOT), a specialist in handling and treating aquaculture solid waste.
Announcing the deal in February, the companies said in a joint statement that Blue Ocean Technology (BOT) will now have the necessary expertise and capital for further growth, which will help it offer fish farmers a way to sustainably utilise sludge resources. Pelagia’s investment in BOT significantly strengthens the company, they said, especially within logistics services related to aquaculture sludge both on land and at sea.
Aquaponics facility
Green fingers
Finally, the waste water from RAS facilities can also be used – as listed earlier – as a resource to help grow plants in an aquaponic system.
A study by researchers at the University of Thessaloniki, Greece, and the Institute of Plant Breeding and Genetic Resources, Hellenic Agricultural Organization-DIMITRA (ELGO-DIMITRA), set out to evaluate the effectiveness of this approach.
Greenhouse production of baby leaf vegetables using rainbow trout wastewater in a high-tech vertical decoupled aquaponic system (Frontiers in Horticulture, July 2024) evaluated a hydroponic system producing baby lettuce and baby rocket plants, cultivated in a deep water culture system using wastewater from a rainbow trout farm.
The results confirmed that aquaponic systems can lead to higher water use efficiency and savings in fertilisers without undermining the yield and quality of lettuce, while the vertical arrangement developed within the scope of the study can increase the land use efficiency of the system.
One day soon, the “circular economy” may become so embedded as a basic tenet of aquaculture that it may no longer even be a buzzword.
