Water Footprint and Wastewater Management in Aquaculture
1. Overview
The rapid growth of the world’s population exerts significant pressure on freshwater resources, energy, seafood supplies, and biodiversity. Therefore, the need for efficient and innovative production models that prioritize environmental sustainability is increasing every day.
In this context, aquaculture, or fish and aquatic organism farming, represents a strategic production method that not only supports the conservation of natural fish stocks but also contributes to sustainable food production.
According to FAO data, aquaculture accounted for 51% of the world’s total aquatic food production as of 2022. This increase demonstrates that controlled production can effectively reduce environmental impacts. In particular, Recirculating Aquaculture Systems (RAS), which enable the treatment and reuse of water, offer a critical solution for sustainable production in regions facing limited water resources.
While aquaculture offers numerous advantages in terms of sustainability and resource efficiency, it also has the potential to create environmental pressures that must be carefully assessed. In particular, the impacts on freshwater resources and aquatic ecosystems are among the most critical aspects requiring attention.
Studies indicate that In 2010, the global freshwater consumption from aquaculture activities (201 × 10⁹ m³) was approximately equivalent to the volume of Lake Toba, and by 2050, it is projected to reach 469 × 10⁹ m³, equivalent to the volume of Lake Erie (Mungkung et al., 2014). This estimate includes only the water used for cultivating plant-based ingredients, such as soybeans,used in fish feeds. When the direct water use associated with aquaculture operations is also considered, the overall water footprint is expected to be even higher.
Water consumption in aquaculture varies significantly depending on the production system employed. For instance, in a traditional flow-through trout farm, approximately 30 m³ of water is required to produce 1 kg of fish, while this figure may reach 45 m³ per kilogram in pond-based systems (Bregnballe, 2015; Verdegem et al., 2006).
In contrast, Recirculating Aquaculture Systems (RAS), where water is continuously treated and reused within a closed-loop configuration, demonstrate much lower water demand. Research shows that RAS operations require only 0.016 to 0.7 m³ of water per kilogram of fish, depending on system density and design (Ahmed & Turchini, 2021). The ability to maintain production with minimal water input makes RAS a critical and sustainable alternative, especially in regions facing water scarcity.
Table 1 below provides a comparative summary of water consumption levels across different aquaculture systems, highlighting the substantial efficiency gains achieved in recirculating systems (Ahmed & Turchini,2021).
Table 1. Water consumption per unit of fish production in aquaculture systems (Ahmed & Turchini, 2021).
|
Aquaculture System |
Water Consumption (m³ water/kg fish) |
Reference |
|
RAS |
||
|
Marine fish production |
0.016 |
Tal et al. (2009) |
|
Fish production |
0.3–3 |
Bregnballe (2015) |
|
Production with advanced technology |
<0.1 |
Martins et al. (2010) |
|
Catfish |
0.5 |
Verdegem et al. (2006) |
|
Eel |
0.7 |
Verdegem et al. (2006) |
|
Turbot |
1.4 |
Verdegem et al. (2006) |
|
Pond Culture |
||
|
Intensive culture |
2.7 |
Verdegem et al. (2006) |
|
Extensive culture |
45 |
Verdegem et al. (2006) |
|
Flow-through System |
||
|
Trout farming |
30 |
Bregnballe (2015) |
2. The Concept of Water Footprint
In aquaculture, the water footprint measures the total volume of water consumed and polluted throughout the production process, providing a basis for assessing its environmental impacts.
This calculation consists of three components:
- Blue water footprint: The amount of surface and groundwater directly used in production.
- Green water footprint: The rainfall water used in cultivating agricultural crops such as soy and corn that are included in fish feed.
- Grey water footprint: The volume of freshwater required to dilute pollutants generated during production.
Analyzing these components forms the foundation for strategic decision-making aimed at improving water management efficiency and reducing environmental impacts.
Findings from Scientific Studies
In a study conducted in Mexico by Guzmán-Luna et al. (2021), the water footprint of producing one ton of tilapia was calculated, revealing that the blue water footprint was the largest component in intensive aquaculture systems.
For the production of 1 ton of tilapia in an intensive system:
- Blue water footprint: 13,027 m³/ton
- Green water footprint: 7,831 m³/ton
- Grey water footprint: 1,873 m³/ton
According to Pahlow et al. (2015), the water footprint resulting from commercial feed production alone reached 31–35 billion m³ in 2008. The species contributing most significantly to this value were Nile tilapia, grass carp, shrimp, common carp, and Atlantic salmon.
To reduce the indirect water footprint associated with feed, researchers are exploring plant-based and insect-based protein alternatives. In particular, insects such as Hermetia illucens (black soldier fly) and Tenebrio molitor (mealworm) are emerging as environmentally friendly substitutes for fishmeal.
3. Wastewater Management
During aquaculture production, wastewater generated from feed residues, metabolic wastes, chemicals, and pharmaceutical residues can lead to eutrophication, oxygen depletion, and loss of biodiversity in aquatic ecosystems.
The main groups of pollutants include:
- Ammonia, nitrite, nitrate: Toxic to fish; cause oxygen depletion and problems such as brown blood disease.
- Phosphorus compounds: Trigger algal blooms and eutrophication.
- Heavy metals, antibiotics, pesticides: Have long-term ecotoxic effects on aquatic organisms and ecosystems.
Selecting and applying appropriate wastewater treatment methods is therefore essential to mitigate these environmental impacts and ensure sustainable aquaculture practices.
Treatment and Sustainable Solutions
Aquaculture wastewater can be treated through physical, biological, and advanced physicochemical technologies:
- Physical methods: sedimentation, screening, filtration, aeration, and flotation.
- Biological methods: activated sludge systems, trickling filters, constructed wetlands, microalgae treatment, and biofloc technology.
- Physicochemical methods: advanced oxidation processes, membrane filtration systems, adsorption, and nanotechnology applications.
Among these, constructed wetlands offer an ecosystem-based solution, enabling the natural removal of nitrogen, phosphorus, metals, and pathogens through the combined action of plants and microorganisms.
In recent years, aquaponic systems have emerged as a model of the “zero-waste” approach, where the symbiotic interaction between fish and plants simultaneously supports wastewater purification and plant production.
While the aquaculture sector holds great potential to meet the rising global demand for food, efficient water use and effective wastewater management remain essential for achieving sustainability.
Water footprint analyses serve as a key tool for optimizing resource use and minimizing environmental impacts. The integration of sustainable feed ingredients, the expansion of recirculating aquaculture systems (RAS), and the adoption of nature-based treatment technologies will form the foundation of future eco-friendly aquaculture production models.
References
Ahmed, N., & Turchini, G. M. (2021). Recirculating aquaculture systems (RAS): Environmental solution and climate change adaptation. Journal of Cleaner Production, 297, 126604. https://doi.org/10.1016/J.JCLEPRO.2021.126604
Bregnballe, J., 2015. A Guide to Recirculation Aquaculture: an Introduction to the New Environmentally Friendly and Highly Productive Closed Fish Farming Systems. FAO and EUROFISH International Organisation, Denmark.
FAO. (2024). The State of World Fisheries and Aquaculture 2024 – Blue Transformation in action. Rome: FAO. doi:https://doi.org/10.4060/cd0683en
Guzm´an-Luna, P., Gerbens-Leenes, P.W., Vaca-Jim´enez, S.D. (2021). The water, energy, and land footprint of tilapia aquaculture in mexico, a comparison of the footprints of fish and meat. Resources, Conservation & Recycling 165, 105224. https://doi.org/10.1016/j.resconrec.2020.105224
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Mungkung , R., Phillips, M., Castine, S., Beveridge, M., Chaiyawannakarn, N., Nawapakpilai, S., Waite, R. (2014). Exploratory analysis of resource demand and the environmental footprint of future aquaculture development using Life Cycle Assessment. WorldFish, Penang, Malaysia. White Paper: 2014-31.
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