Seeking a revolution in freshwater aquaculture
This article was featured in Eurofish Magazine 3 2024
SmartAqua4FuturE (SAFE) is an ambitious project funded by Horizon Europe that aims to revolutionise freshwater aquaculture. The project seeks to make freshwater aquaculture more environmentally friendly while increasing its financial stability by introducing circular economy approaches.
The world’s aquaculture production has increased by 54% since 2011 and remains one of the fastest-growing food production sectors, with an expected additional growth of 35% by 2030, according to the UN Food and Agriculture Organisation (FAO). Aquaculture growth within the European Union has, however, not seen a similar development and investments in this growth sector are therefore being encouraged by the European Commission.
One project that fits directly into this focus area is SAFE. This €4.5m Horizon Europe project aims to reduce the environmental impact and improve the economic viability of freshwater aquaculture by valorising unused resources like solid and liquid waste streams from systems based on recirculating aquaculture (RAS) and integrated multi-trophic aquaculture (IMTA).
Launched in 2022 with 13 partners from nine countries across Europe, the diverse objectives of the SAFE project will be achieved through several work packages.
Aquaculture waste stream characterisation
SAFE aims to reduce the nutrient emissions from freshwater aquaculture systems by utilising liquid and solid effluents in biomass production. A baseline of the selected systems was first determined to assess the suitability and safety of the effluents as substrates for microalgae, mushrooms, redworms, and plant production and to quantify the effect of SAFE solutions.
The study sites in SAFE include RAS (Finnforel, in Finland), IMTA (Keywater, in Ireland), pond (ICR, in Poland,) and flow-through (Måsøval Åsen Settefisk, in Norway) systems. The systems have been sampled at least four times between November 2022 and February 2024 to take into account seasonal variations in the quality of incoming water, effluent, and sludge. Samples have also been collected from the intermittent stages of the process. The samples have been analysed for macronutrients and trace elements with additional analyses (e.g. pesticides, antibiotics, and particle size) depending on site-specific needs and the subsequent use as substrates. The analyses have been done locally (outsourced service/ in-house laboratories) and by consortium partners according to ISO standards and in-house protocols. The operators have provided additional environmental data such as pH and temperature. The sediment build-up in ponds (Poland) has been assessed by installing sonar technology and sampling cylinders at the bottom of 10 selected ponds in Poland.
The results indicate no concerns regarding heavy metals, pesticides, and antibiotics. The constructed wetlands at Keywater and the treatment process at Finnforel efficiently reduce phosphorus discharges, whereas at the ICR farm there is no reduction of phosphorus levels from ponds to the discharge channel, highlighting the need for additional solutions to be tested in SAFE.
Innovation in aquaculture
The project has produced a broad overview of current technologies and innovative concepts applied in the broader aquaculture sector, providing insights into current developments with potential applications for freshwater aquaculture production in the EU. It encompasses 55 state-of-the-art technological innovations spanning six main areas of innovation: Production system designs, waste management, aquafeed development, genetic improvement, disease prevention, and digital innovations. This provides a foundation on which the project can build and, in SAFE, has resulted in a prototype of a low-cost and natural filtering system for pond aquaculture using straw bales acting as a sieve. The system reduces the discharge of sediments from the ponds during their seasonal draining by altering the discharge water flow. Based on this prototype, a full-scale filtration system was developed in operational conditions at the ICR farm consisting of 69 sets of 3 straw bales arranged in a herring-bone shape along 134 metres of the drainage channel, diverting the water and forcing it to slow down and release its sediments. These straw bales enriched with sediments were subsequently tested as a substrate for oyster mushroom (Pleurotus ostreatus) cultivation (see below).
The project designed a novel CO2 heat pump for RAS systems to be used with an existing dryer that will better enable the drying and exploitation of sludge from RAS farms. The implementation and installation at an operational RAS farm have not yet taken place.
Biodiversity assessment
The project also evaluates the impact of different aquaculture systems on local biodiversity before and after applying SAFE technologies/models in IMTA systems in common carp (ICR) and perch farms (Keywater). For reference, the impacts of a flow-through system with sludge collection on biodiversity were assessed for a salmon smolt farm in Norway.
The impact of the reference farm on the aquatic environment was assessed in summer, autumn and winter. A set of physiochemical parameters (e.g. pH, O2 level, conductivity, temperature) were characterised in water samples collected from Lake Ulen. Additionally, sonar technology was applied to prepare bathymetric maps of the lake and samples of macrobenthos (e.g. water mites) were collected at different depths. Furthermore, a spring sampling campaign in Norway is currently planned.
The seasonal sampling campaign at the selected sampling sites in the proximity of the Keywater farm in Ireland has been completed, the species diversity of benthic invertebrates assessed, and diatom samples are being analysed.
At the ICR farm (Poland), benthic diatom and macroinvertebrate samples from the inflow and outflow channels were collected during different seasons (spring, summer, autumn, and winter). To assess how the straw bale filtering system improves biodiversity downstream the farm, three water quality bioindicators, i.e., noble crayfish (Astacus astacus), thick-shelled river mussel (Unio crassus), and river water crowfoot (Ranunculus fluitans) were placed in water and their condition monitored.
Machine learning and image-based sizing tool
To enhance the management of fish biomass, with a particular focus on improving grading processes, the SAFE project seeks to minimise the handling of fish, reduce variability in weight, and maximise the efficiency of resource allocation during fish transfers. This will be achieved by developing a Discrete Event Systems (DES) simulator, designed to model fish growth and weight distribution considering various rearing conditions such as water quality, temperature, and salinity. Complementing this simulator, a machine-learning model has been devised to predict growth patterns based on the simulator’s calibrated outcomes. This predictive model serves as a critical component of an optimisation framework for grading and resource management.
A key feature of the system is an imaging-based fish measurement tool. This innovative tool facilitates growth monitoring and data gathering on fish size and weight directly in their habitat, eliminating the need for physical handling and thus reducing stress and disease risk. The SAFE project developed this tool using advanced deep-learning techniques for image segmentation, identifying fish silhouettes in images taken above the tanks. Concurrently, an allometric model calculates the fish weights from these dimensions. This system can moderate the feed rates and measure water quality parameters in the experimental tanks.
Moving forward, this tool will enter a crucial phase involving the collection of empirical data from laboratory experiments and field studies at aquaculture facilities. This data will not only facilitate the calibration of the simulator but also provide the essential information needed to train and fine-tune the machine-learning model. This comprehensive approach aims to significantly enhance the precision of fish stock management practices, ensuring sustainable and efficient operations.
Microalgae cultivation
The algae cultivation has been conducted using processed wastewater from the Finnforel RAS farm. In the initial growth trials with diatom Phaeodactylum tricornutum, the RAS water was optimised by adding phosphorus and certain trace elements (e.g. Mn). Grazer (flagellates, ciliates) contamination appeared to be a significant issue that collapsed the cultures. The tests showed that to secure the purity of the water used for algal cultivation, the RAS wastewater needs to be filtered through a <1 µm filter and treated with UVC before being used as a growing medium. In addition, the cultivation unit should be closed to prevent contamination from the air.
Following the preliminary tests, the cultures were upscaled from 5 to 300 litres. The cultures in batch mode did not reach N-limitation, and hence, the cultivation mode was changed to semi-continuous with weekly/biweekly harvesting by settling the biomass and collecting the settled material. To boost lipid production, the collected biomass was then cultivated in batch mode until it was N-deficient (ca. 5 days), “after which it was centrifuged and frozen at -20 °C. The biomass was dried by freeze-drying, after which it was immediately vacuum-packed to prevent the oxidation of lipids., after which it was immediately vacuum-packed to prevent the oxidation of lipids.
/Algae%20pictures/P_tricornutum/Dry%20biomass.jpg?csf=1&web=1&e=1Gyakx){kind=link}
The algal biomass production for fish feed trials and the optimisation of lipid production are in process. Trials with fish sludge from RAS and experiments on bioflocculation are planned for the upcoming year.
Aquaponics
Testing of decoupled aquaponics began in late April 2023 to investigate the utilisation of liquid effluent from RAS to cultivate edible vegetables and fruits in a greenhouse environment. SAFE experimented with different types of aquaponics systems, including nutrient film technique, bell siphon technique, and flow through. A variety of plants, including spinach, various types of lettuce, mint, swiss chard, and watercress, were also tested, as were hops and grapes, in a separate outdoor soil-filled container.
On a daily basis, 30 L of RAS waste was added to the aquaponics system to monitor the resulting changes in water quality. Overall, the different decoupled aquaponics systems worked very well, with all the plants showing positive growth trends while maintaining good water quality. One trend that became obvious was the high PO4 levels, which will be further investigated in the coming growing season. A total biomass of 18 kg was produced during the growing season, which ended in Oct 2023. For the colder winter, researchers are comparing wild growth with commercial watercress plants.
Mushroom production with dried sludge looks promising
So far, two materials have been evaluated as potential ingredients in substrates for the oyster mushroom (Pleurotus ostreatus) cultivation, namely, the straw bales enriched with sediments from common carp pond farming, as previously mentioned, and insect frass from mealworm (Tenebrio molitor).
The straw bales enriched with sediments were used as an ingredient for mushroom production at different percentages (0%, 25%, 50%, 75%, and 100%) mixed with a commercial mushroom substrate. The best yields were obtained with the inclusion level of 25%, followed closely by 50% and 75%, all exceeding the control group. Only a 100% inclusion level resulted in lower yields compared to the control.
The mealworm insect frass was also used as an ingredient for mushroom production at different percentages (0%, 15%, 30%, 45%, and 65%) mixed with the commercial mushroom substrate. The best yield results were obtained with a 15% proportion. Since the yields with high percentages (>15%) were lower than the control values, the trials were repeated using the insect frass supplement in smaller quantities to find the optimal share. The second trial was performed with inclusions of 2.5%, 5%, 7.5%, 10%, 12.5% and 15% of frass. This trial showed that 2.5% gave the best results, exceeding the control yield.
A commercial-scale trial with straw bales enriched with carp farm sediments has been successfully accomplished, and a full-scale mushroom production using an innovative substrate from the carp farm has been demonstrated. The stems were dried using traditional drier and Waister drying technology (Waister AS, Norway), and the ground material was sent to the different partners to produce feeds for upcoming fish trials. The post-cultivation substrate from this trial will be dried and used as an ingredient for mealworm production. Trials will also be undertaken with dried fish sludge from a salmon RAS farm as a mushroom growing substrate.
Redworm production
Redworm (Eisenia fetida) production started in April 2023. The worms were housed and grown in box containers in a 6.1 m insulated steel container. Each polystyrene box is filled with compost and 1 kg of worms. Duckweed from IMTA ponds is harvested and mixed with the compost along with fish waste from the Keywater RAS, to provide a food source for the worms.
For the first three months, the worms used duckweed and sludge as a feed source, but they had limited maturity and reproduction after this point. The project is therefore conducting trials to investigate various ratios of duckweed to fish waste to make it more appealing for the redworms. SAFE is designing a workshop on on-site redworm rearing for carp farmers, which is planned for Poland’s National Carp Conference in September 2024.
Mealworms
Three different substrates were tested for mealworm production: duckweed, watercress, and the spent mushroom substrate (SMS) from straw bale cultivation (as described above). The mealworm production was carried out by breeding larvae of a known age in laboratory scale boxes filled with the substrates in a defined mass ratio for four weeks. On a weekly basis, the excrement, the larvae biomass, and the remaining substrate were weighed, and the feed was replenished.
The results of utilising watercress and duckweed biomass for mushroom culture showed that none of the samples performed better than the control group. Neither of these by-products improved the growth of mealworms. In contrast, the less watercress or duckweed, the better they grow. Therefore, future biomass will be produced based on the oyster mushroom SMS instead.
The SMS used for mushroom production at different percentages (0%, 25%, 50%, 75%, and 100%) was first evaluated and mixed in with the control diet used, which is based on cereals. An experiment using only the control diet was also carried out. The substrates with 25% and 75% of SMS grew 14% and 11% higher than the conventional substrate in mealworms, respectively. The performance of the rest of the substrates (0%, 50%, and 100%) was similar to the control. This suggests that the use of this by-product can both improve and accelerate the growth of these insects.
Looking ahead
The SAFE project represents a significant step towards a more sustainable future for freshwater aquaculture. By applying circular economy concepts and introducing innovative technologies, the project aims to reduce the environmental impact of freshwater aquaculture systems and improve their economic viability. The preliminary results after only 18 months demonstrate the potential of these approaches and provide a solid foundation for the ongoing work of the SAFE project. The project’s success will benefit the aquaculture industry and contribute to the broader goal of sustainable development. The lessons learned from the SAFE project can also be applied to other sectors, making it a valuable resource for anyone interested in sustainability and innovation.
For more information, contact:
Thomas Jensen, Eurofish
contact@projectsafe.eu
www.projectsafe.eu