Introduction
Aquaculture is increasingly considered as the main source for meeting the world’s growing demand for fish products (FAO, 2022) . However, in parallel with the growth of the sector, concern about its sustainability has also grown. In this regard, the SIMTAP project “self-sufficient integrated multi-trophic aquaponics systems’ (EU PRIMA 2018) aims to implement and test a multi- trophic aquaponic system to reduce: (i) fish meal and fish oil use for feed (ii) water and energy consumption, (iii) emission of nutrient compounds. These are the main factors identified as environmental hotspots in aquaculture systems ( Aubin et al., 2009; Abdou et al., 2017 ). In particular, the proposed system allows for the recovery wastewater from aquaculture and its use as a nutrient source for hydroponics, achieving a run-off reduction and nutrient recovery effect as well as the co-production of other alternative food and/or feed. In addition, the project aims to analyze its performance in terms of sustainability and, for the environmental pillar, Life Cycle Assessment (LCA) approach is considered the most suitable methodology to apply. In this study, using the LCA method , the environmental performance of SIMTAP systems developed in Italy were analysed and compared with that of a traditional aquaculture inland farm.
Materials and method
The concept behind the analysed SIMTAP system is to utilise wastewater from the rearing of Gilthead Sea bream (Sparus aurata) and European Sea bass (Dicentrarchus labrax ) for both a hydroponic halophytic system (for Salicornia, Salicornia europaea and Beta Maritima, Beta vulgaris subsp. maritima), which exploits the dissolved nutrients in the water, and for the breeding of DFFO (polychaetes ) that feed on the solid waste from the fish, in order to recycle the the nutrient in the water loop .
The functional unit (FU) selected for the LCA (i.e. the reference unit of the study to which all inputs and outputs are referred) was 100 kcal derived from all the outputs of the systems analysed (fish, S alicornia, Beta maritima, polychaetes). This FU was chosen because it expresses the functionality of the food (McLaren et al., 2021) while at the same time allowing the different outputs of the SIMTAP sy stem to be taken into account. We applied cradle to farm gate perspective for the definition of the system boundaries, including the production of the infrastructure and equipment (e.g. pumps, tanks, filters), the production of inputs (e.g. electricity, diesel, liquid oxygen), feeds production and supply and the net nutrient emission due to the metabolism of the fish. To facilitate the comparison of results with a commercial reference system, the scenario inventory was built by up scaling the experimental data and results of the pilot plant to a production farm of 10 tonnes of fish/year. To this purpose, literature data , estimates and questionnaires submitted to experts were also used. In particular, two scenarios were constructed that differ in terms of fish feeding: (I) commercial feed (CF) scenario in which fish are fed with a commercial feed; (II) alternative feed (AF) scenario: in which fish are fed with an alternative feed consisting of locally produced mussels, clams and polychaetes.
The commercial reference farm, used as a benchmark, is a traditional Italian inland farm with a production of about 400 tonnes/year of Sea bream and Sea bass. T his farm consists of several ponds, where fish are reared from a size of 3g up to 400-500g. The system is high energy demanding, both for pumping water, blowers and the liquid oxygen consumed.
Results
For the main impact categories analysed in the aquaculture sector (global warming potential, eutrophication, cu mulative energy demand, acidification ) the two SIMTAP scenarios always have a lower impact than the commercial farm. In more details, the global warming potential is 0.230, 0.247 and 0.266 kg CO2 eq./100 kcal respectively for CF scenario, AF scenario and commercial farm. The cumulative energy demand is reduced b y 25% in both SIMTAP scenarios, while the most promising results are in the eutrophication impact category. This category depends mostly on the release of nitrogen and phosphorous compounds into the environment due to fish metabolism. In SIMTAP systems, thanks to the coupling of the hydroponic system (which absorbs the dissolved part of the nutrients) and polychaetes (DFFO that feed on fish faeces, removing the solid part of the waste), eutrophication is significantly reduced (more than 50% reduction). However, the main hotspots of the analysis, as in the commercial farm, remain the high electricity consumption due to pumping water, oxygen consumption and feed supply. Furthermore, since a large surface area is required for the hydroponic system, the impact of the infrastructure required for the system is also not negligible.
Conclusions
Improving the sustainability of aquaculture is a need in the current European context. As demonstrated in this study, f ollowing the example of the SIMTAP system, it is possible to improve the environmental performance of aquaculture systems with new diets characterised by the use of locally produced raw materials, the coupling of a hydroponic system to a RAS and the reuse of nutrients. Furthermore, in a context where energy consumption is the main driver, maximisation of the use of renewable energy sources (e.g. solar energy) can lead to significant improvements. I t is important to emphasise that the analysis is concerned with theoretical scenarios, so the analysis of the uncertainty of data and results will be a further important step. Finally, in addition to environmental performance, economic and social sustainability should also be assessed for a more comprehensive evaluation of the innovative systems.
Acknowledgements
This study was conducted within the framework of PRIMA S2 2018 project SIMTAP. SIMTAP (https://www.simtap.eu/) is part of the PRIMA Programme supported by the European Union.
References
- FAO. (2022). The State of World Fisheries and Aquaculture 2022. Towards Blue Transformation. Rome, FAO. https://doi.org/10.4060/cc0461en.
- Aubin, J., Papatryphon, E., Van der Werf, H. M. G., & Chatzifotis, S. (2009). Assessment of the environmental impact of carnivorous finfish production systems using life cycle assessment. Journal of Cleaner production, 17(3), 354-361. https://doi.org/10.1016/j.jclepro.2008.08.008
- Abdou, K., Aubin, J., Romdhane, M. S., Le Loc’h, F., & Lasram, F. B. R. (2017). Environmental assessment of seabass (Dicentrarchus labrax) and seabream (Sparus aurata) farming from a life cycle perspective: A case study of a Tunisian aquaculture farm. Aquaculture, 471, 204-212. https://doi.org/10.1016/j.aquaculture.2017.01.019.
- McLaren, S., Berardy, A., Henderson, A., Holden, N., Huppertz T.,…van Zanten, H. (2021). Integration of environment and nutrition in life cycle assessment of food items: opportunities and challenges. Rome, FAO. https://doi.org/10.4060/cb8054en