Creating energy from fish waste

According to research from the University of Gothenburg, fish and vegetable farms (aquaponics) may be able to produce biogas that can be fed back to the energy system of the farm by digesting fish waste. This could also generate excellent nutrition for plants.

Often referred to as aquaponics, circular, land-based, combined fish and vegetable farms are increasing in growth. The system makes use of nutrient-rich water produced by fish which can be used to fertilise plants in a closed, soil-less system with the help of bacteria that grow naturally within the systems. These models imitate the fertilisation that occurs in river and lake ecosystems.

Until now, the solid waste of fish has been a by-product with no particular value. But the research project has used the waste to make biogas that can contribute to meeting the energy needs of the aquaponics farms.

According to Victor Lobanov, doctoral student of marine biology at the University of Gothenburg, fish faecal matter can be broken down via anaerobic digestion, creating a concentrated gas mixture of 70% methane that can be used as fuel.

The nutrients released in the digestion of waste are also more easily available for plants compared to synthetic nutrition solutions.

“Fish waste contains a lot of nutrients. These should also be usable in aquaponics to enable even more sustainable food production than today,” Lobanov said.

Carbon dioxide is produced when the biogas is used as fuel, which is a necessary supplement when plants are grown in an enclosed space, like a greenhouse.

The digestion process has only been tested in a lab environment so far, but a pilot in a commercial facility is set to begin later in the year. It will give researchers insights into how well the method can handle perturbations to the system and what needs to be done to create a more robust digestion pipeline.

Lobanov aims to create modular digestion systems that can be integrated into existing aquaculture and aquaponic facilities.

There is significant interest from the industry as this technology could be used in other animal husbandry applications such as piggeries. The sludge left over after digestion is nutritious and can be used for traditional fertilisation of fields. In this process, the residual sludge left over and its eutrophication potential are reduced.

“In many countries, the quantity of fertiliser produced in livestock farming is a problem. It can only be spread on fields during certain times of the year, and removing wastes from the farm is associated with extra costs during pumping and transportation. Digestion of the fish solids reduces the quantity of waste produced by farms while additionally producing energy and a great fertiliser for hydroponics,” Lobanov said.

Image credit: Victor Lobanov