iFishIENCi Valorisation of by-products and sludge
Creators: name: Balsells, Sandra
name: Gal.la, Ramis
name: Kleinegris, Dorinde
name: Boccadoro, Catherine
name: Ramanand, Sreerekha
name: Cusimano, Giovanni Marco
name: Prescott, Steven
name: Durand, Dominique
name: Eusha, Muhammad
name: Pereira, Fabio
name: Paolacci, Simona
Publisher: name: Zenodo
Year: 2024
Subjects: Valorisation
aquaculture
by-products
waste
sludge

description: The iFishIENCi project, WP1 – Task 1.5 Zero waste and valorisation of by-products and sludge aims to design condition-based optimal valorisation processes for waste recirculation from aquaculture effluents for the recovery of nutrients (nitrogen, phosphorus, and carbon) within a circular economy. The valorisation processes were used for the production of the two iFishIENCi sustainable feed, namely microalgae and yeast (Task 1.3), and feed ingredients. Their sustainability and circularity were further evaluated as part of WP4.

The objective of task 1.5 is to identify and demonstrate potential valorisation routes for fish farming waste streams and by-products within a circular economy and zero waste strategy, taking into account all effluents generated within the whole value chain, from the production of ingredients (feeds) to fish farms themselves. The deliverable D.1.6 Valorisation of by-products and sludge details waste identification, collection plan, characterisation, selection for valorisation trials, methodologies, and results.

Identification, monitoring, and characterisation of different waste streams were investigated (LEITAT, NORCE) for the production of new feed (algae, yeast). MATE and ABT optimized waste collection and monitoring methods by testing the smart feeding technology (Product 3: SMART-RAS) and then demonstrating removal efficiency with swirl separators of 63% of Total Suspended Solids (TSS), with 79% of total N available for valorisation (WP2 and WP3). According to the characterisation of the various waste streams and taking the regulatory framework into account (assessed in WP4), two main sources of waste were selected to be investigated through different valorisation trials under a circular approach and towards zero-waste strategy: waste from the iFishIENCi test-sites from RAS system (ABT, AA) and Land-based flow-through system (GyE). Furthermore, the analysis of the different waste compositions provided the necessary information on carbon, nutrients, and mineral content to identify and select a number of key microorganisms (bacteria and fungi), used in industrial bioprocesses, and test their growth potential on RAS-waste as feedstock. Recommendation on priorities for further investigations are given.

As a result of the experiments for the reuse of dirty water as substrate for algae production conducted at pilot level as proof of principle (NORCE), it was proved that the outlet water from all fish production from RAS and land-based flow-through systems could be directly usable for the cultivation of photoautotrophic microalgae (e.g., Nannochloropsis gaditana). All batches of wastewater were found low in nutrient concentrations, phosphate being the main limiting nutrient for the microalgae. Therefore, process and/or reactor design to ensure high biomass productivity while treating large amounts of water is therefore necessary.

Additional experiments were conducted on the yeast (Candida utilis). Candida could not grow on wastewater from RAS as feedstock, but significant growth was obtained on sludge, after appropriate pre-treatments (dilution, centrifugation to eliminate the insoluble material, and double autoclaving to kill all the microorganisms and spores).

A new methodology was developed to produce nutrients for microalgae and yeast feeding using concentrated sludge from RAS. The process involved pretreatments (ultrasounds), followed by enzymatic processes (endo and exoprotease) and chemical (KOH). The resulting total nutrient recovery from waste was 36-46% nitrogen, 3-8% total phosphorus, and 13-60% total organic carbon, depending on the method. Nutrients extracted from concentrated RAS sludge, showed a good potential to be used as nutrients source for microalgae cultivation, in some specific cases, and as carbon and energy source for yeast production.

Besides the use of these nutrients for biomass production (algae, yeast) and as part of Waste2value, the medium ingredient obtained was characterized for potential use as fertilizing product in agriculture, showing promising potential.

The residue of this new process as well as the resulting residual fractions from the production of new feeds were also analysed for potential use as fertilizer, toward zero waste strategies. The residue showed promising characteristics, except for slightly above-permit cadmium levels. Further research is needed to assess pollutants under European and national fertilizer regulations.