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Waste not: converting RAS fish waste to fertilizer, biocoal, other opportunities

Fish sludge, the very name easily conjures images of the mess it creates. Made up of fish feces and undigested excess feed, this aquaculture waste product is a top headache for recirculating aquaculture system (RAS) operators.

Sludge is an ideal breeding ground for disease-causing bacteria and it clogs up systems. Getting rid of it is expensive, and the more biomass you produce, the more fish sludge you get.

In this article, we investigate the contrasting waste conversion strategies adopted by two dissimilar companies that embraced fish waste recycling in different phases of their company’s growth.

From problem to profit

The agriculture industry has already developed advanced methods of converting animal waste however, the RAS industry is catching up, according to Abhinav Choudhury, PhD, an environmental research engineer at the Freshwater Institute.

“Mature waste conversion technologies and business models already exist for terrestrial animal farms,” says Choudhury. 

The Conservation Fund’s Freshwater Institute specializes in researching sustainable development of the US aquaculture industry. Choudhury’s work focuses on a waste-to-value program and his team is currently researching the potential of creating value from aquaculture waste for a RAS farmer.

The growing interest in the RAS around this area is driven by three key factors, according to Choudhury:

1. The potential for increased revenue or economic returns through the utilization of the organic matter and nutrients in the waste stream to offset high capital expenditure and operational expenditure of RAS farms. 
2. Reduction in the environmental impacts caused by discharged wastewater into lakes other bodies of water or landfill.
3. Increased scrutiny of the public and strict government regulations to protect the local watershed. 

Early converts

Todd Deligan, the general manager of the North American arm of Norway’s Salmon Evolution, would be happy if the industry could move away from calling fish sludge, fish sludge or fish waste. Its decades-old moniker just doesn’t suit the potential that fish sludge has, according to Deligan.

RAS companies are looking at the potential of fish sludge as a “second harvest” for profit.

“The industry really has to come up with a better name for this product that holds a lot of economical and ecological potential,” says Deligan.

Salmon Evolution operates one of Europe’s largest land-based fish farms at Indre Harøy in the west coast of Norway. The hybrid flowthrough/RAS facility was designed for a total annual production capacity of 31,500 tonnes head-on gutted salmon. 

Sustainability is a key component of company’s construction and production strategy from the get-go. For instance, Indre Harøy is fully powered by renewable electricity from a nearby hydropower plant.

“Environmental sustainability was always part of the conversation,” says Deligan. “The concept of treating effluent and being able to recycle solid waste was part of the company strategy since Day One.”

In 2021, Salmon Evolution signed a contract with Blue Ocean Technology, to provide the RAS company with a complete treatment package for washing, disinfecting, dewatering and drying sludge. 

Blue Ocean Technology develops systems that users can program to convert sludge for various uses such as biocoal, fertilizer, biogas, or compost.

Salmon Evolution does not use the product directly.

“Today, we are having to pay to take the solids away to a biogas plant,” explains Deligan. “Our core business is sustainably producing high-quality salmon. For us, waste conversion is not a revenue stream. This is a cost we are willing to pay. We want to support a circular economy.”

“Treating wastewater and reusing fish sludge to produce, for example, biogas and short-travelled fertiliser are among our contributions to a circular economy,” states the company’s 2022 annual report. 

“As part of Salmon Evolution commitment to a truly sustainable production and circular economy, waste is filtered and collected, before being transported to a recirculation plant where it is converted into fertilizer, biogas or similar.”

This strategy will be part of Salmon Evolution’s business model for its unfolding North American expansion, according Deligan.

Home and garden approach

Great Falls Aquaculture, in Turner Falls, Mass., is one the biggest RAS grower of barramundi in the U.S. 

Keith Wilda and business partner James Malandrinos own Great Falls. The two men also own Blue Stream Aquaculture-New Hampshire which produces trout, and Blue Stream Aquaculture-Cape Cod, a trout hatchery in West Barnstable, Mass.

All three companies do not only sell fish, they also produce and market a whole line of organic soil supplements and fertilizers for lawns, gardens, farms, and orchards. Source from various mixtures of nutrient-rich RAS sludge, fish scraps and organic ingredients, the products are sold under the brand Fish Brew. Fish Brew branded t-shirts and baseball caps are even available from the website for fans.

Great Falls Aquaculture was bought by its current owners in 2018, and Fish Brew became part of the business just around 2021. 

However, using waste to help plants grow was something facility workers had been doing even before then, according to Spencer Gowan, general manager at Great Falls since 2018. Gowan also worked as a production manager from 2015 to 2019, when Australis Aquaculture was still the owner of Great Falls Aquaculture.

“You would always hear stories of employees collecting sludge, solid waste or fish scraps and using it in their home gardens,” said Gowan. “They would often come back to share their massive squashes, tomatoes and other New England veggies.”

Gowan attributes the start of the eventual development of what would be known as Fish Brew to Walker Wright-Moore, current nursery manager at Great Falls Aquaculture.

Wright-Moore was working as a fish culture specialist for Australis Aquaculture when he began developing a fish hydrolysate, a product for promoting plant growth.

“He was building a garden bed, and he began researching regenerative gardening,” recounts Gowan. “Then he started asking people about their use of fish scraps and fish waste as fertilizer.”

Regenerative gardening is an ecosystem-based approach to gardening. It seeks to improve plant resilience and growth through by improving soil health and water quality, improving biodiversity, and reducing synthetic inputs.

Wright-Moore began developing a fish hydrolysate, by putting dried-up fish scraps into a meat grinder and adding other ingredients such as rice wash, probiotic and sugar.

“He came us with a product that had good NPK value,” says Gowan. 

NPK stands for nitrogen, phosphorous, and potassium – the three macro nutrients used by plants. NPK numbers indicate the percentage of these three elements in a fertilizer. The higher number of a one of these elements indicate a greater concentration of this element in the fertilizer. Different plants and soils require different NPK combinations.

“Wright-Moore approached Australis with his product, but they didn’t have time for it. They just allowed him to collect more scraps,” says Gowan. “It was only when Great Falls Aquaculture came under new ownership that Wright-Moore got the help to further develop the product, determine the proper enzymes to use and streamline production.”

“We are also found out that each of our farms produced different nutrients, algae, beneficial fungi and bacteria,” Gowan adds. “If we alter the mixture, we can produce different products that provide different benefits.”

Today, the Great Falls Aquaculture sells Fish Brew Hydrolysate along with Fish Brew Epic FLO probiotic for hydroponic growth; Fish Brew Pro FLO probiotic, and Rise and Thrive, soil conditioner.

Currently, Great Falls Aquaculture wastewater goes through a water treatment and solids treatment system. A series of drum filters to separate solid waste from the water. The solid waste from all three fish farms is combined. Part goes to the municipal treatment plant and some are added into the Fish Brew products.

Great Falls Aquaculture will soon purchase a screw press to compact this nutrient-rich solid waste into cakes which it intends to sell for farm use or for creating compost.

The company also plans to install an anaerobic digester to convert sludge into bioenergy. 

Dr. Abhinav Choudhury examining samples of MBR at the Freshwater Institute’s research facility. (Photo: Freshwater Institute)

The next step

Anaerobic digestion is used to generate bioenergy for terrestrial farms, a liquid fertilizer to meet nutrient requirements for crops, and a solid product that is either composted and sold, or used on-site as bedding for the animals, says Choudhury.

Abhinav Choudhury

Anaerobic digestion involves a series of biochemical processes where microorganisms break down sludge, without the use of oxygen.

“I have not seen a whole lot of technologies like anaerobic digestion deployed commercially for converting aquaculture waste into valuable products,” he adds. “Simple waste treatment solutions like mechanical filtering, gravitational thickening or addition of coagulants for solid separation, and sludge drying are more common.”

These solutions are effective at reducing sludge volume, but they rarely utilize the organic matter and nutrients in the waste to generate additional value for a RAS farmer, says Choudhury.

“Understanding the knowledge gaps to adapt these technologies to aquaculture waste is the first step, according to the scientist. The next step would be to develop innovative fresh solutions specific to aquaculture waste so farmers can have a plethora of options to choose from to meet the specific requirements of their farms,” says Choudhury.

Word to the wise

Waste conversion is still in its pilot stages in the RAS industry.

Companies interested in checking it out could benefit from this advise from Choudhury: 

Plan – Waste conversion/management should not be an afterthought. Creating a sellable product from the waste may help offset operating costs. When planning the project, hire or consult waste experts in addition to fish experts.

Permitting pain points – RAS is a recent technology and regulators in many jurisdictions may still be investigating how to classify waste streams from RAS farms. Make sure you begin discussions with local natural resources protection departments in your area of operation. They can help you identify the applicable waste management practices for your facility and the accompanying required permits.

Loans and grants  – Investigate sources of government loans, grants, and other support for waste conversion technologies and programs.

Track trade-offs – Different waste conversion strategies come with their own associated trade-off. A simple waste treatment solution may look attractive initially but could result in higher expenses (stricter regulations, increased cost of transportation, higher landfill costs, etc.). Conversely, a complex waste conversion technology could be challenging to operate, and a competent operator may be necessary to ensure its long-term successful operation.

Data sharing – Sharing experiences and challenges with both waste and fish researchers or experts can also lead to the development of farm-specific solutions. 

Choudhury, Gowan and Deligan agree on one thing: Never ignore waste.

Regulations around aquaculture waste are becoming more stringent. RAS farmers need to be proactive in their waste management efforts. The industry should start seeing waste as an opportunity rather than a problem.