NAFi aims to establish a production cycle consisting of fish aquaculture, microalgae production and aquaculture sludge utilisation and to optimise the nutrient and economic balance.
All nutrient streams, especially process water from fish farming and aquaculture sludge, are to be utilised in the sense of a circular economy. The model site is located in Gönnebek in Schleswig-Holstein.
With the growing awareness of the consequences of global eutrophication and the finite nature of phosphorus deposits, the need for systems that enable efficient nutrient utilisation is increasing.
Aquaponics systems, i.e. combined aquacultures that utilise their process water for plant cultivation, are now established, but are rarely profitable enough for long-term economic viability. In NaFi, microalgae are also used in water treatment for optimisation.
Innovations and advantages of the NaFi project
1. microalgae complement land plant cultivation:
- Direct nutrient utilisation: microalgae can directly utilise the nitrogen (ammonium) and phosphorus (phosphate) released by fish without the need for a correspondingly large biofilter, creating useful biomass rather than just taking up space.
- Higher removal rates: Microalgae have higher growth rates than terrestrial plants and convert nitrogen and phosphorus directly into aquaponically useful compounds.
- Stable pH value: Microalgae raise the pH value through photosynthesis, which reduces the artificial addition of alkaline salts.
- Oxygen enrichment: Microalgae release oxygen into the process water, which reduces the need for external oxygen supply for fish farming.
- Thermal energy: Microalgae bioreactors can provide excess heat for warm water fish farming or can be fed into the local heating network.
2. utilisation of aquaculture sludge:
- Vermicomposting: Earthworms decompose the sludge quickly, reduce unwanted microorganisms and produce high-quality fertiliser in the form of worm humus and worm tea, which also enables pH adjustment in crop cultivation.
- Seed coating: The sludge serves as a nutrient source for an innovative ecological coating of biochar and superabsorbers that can replace mineral fertilisers.
These approaches represent an almost closed-loop economy, save energy costs and conserve resources compared to conventional production methods.
