The global aquaculture industry is booming, but its success hinges on effective waste and effluent management. Nutrient-rich water discharged by intensive fish and shellfish farms can wreak havoc on surrounding ecosystems, leading to algal blooms and oxygen depletion. So, how can we ensure this vital food source thrives while also protecting our precious water resources?
A team of researchers from Griffith University (Australia) and the Department of Environment and Science (Australia) published a scientific review examining the nutrient inflows and outflows of intensive aquaculture ponds and identifies approaches/technologies being used to reduce nutrient loads and thus downstream impacts.
Pond-based Aquaculture
While aquaculture methods vary, pond-based systems are widely used for raising fish and crustaceans. Though a comprehensive picture is lacking, satellite data estimate over 3.4 million aquaculture ponds exist solely in coastal zones of South, Southeast, and East Asia, covering an astonishing 2 million hectares.
Need for Responsible Intensification
The Food and Agriculture Organization (FAO) predicts a 15% increase in aquatic food production by 2030, primarily driven by aquaculture expansion and intensification. Intensification essentially means producing more on less land.
While increasing production is necessary, doing so responsibly is crucial. Traditionally, aquaculture intensity has been defined by factors like population density and food sources. However, these definitions are constantly evolving as technology and practices improve. While “super-intensive” systems with extremely high population densities exist, prioritizing sustainability is essential.
The Challenge: Nutrient Overload
Intensification often leads to higher nutrient loads within ponds, which can then be discharged into surrounding water bodies. Formulated feeds are one of the main culprits of nutrient pollution. While advancements in feed production have shown promise in waste reduction, more needs to be done. Wastewater treatment poses another challenge, as it can have significant negative consequences, including:
- Algal blooms: Excess nutrients can drive excessive algae growth, leading to oxygen depletion and harming aquatic life.
- Water quality degradation: Nutrient pollution can disrupt the delicate balance of marine and freshwater ecosystems.
- Impact on aquatic ecosystems: Discharged nutrients can negatively affect rivers, estuaries, and coastal areas.
Treatment Options: A Spectrum of Solutions
There are several options for treating aquaculture wastewater, each with its own advantages and limitations:
- Low-cost solutions: Settling ponds are affordable but have limited effectiveness in nutrient removal.
- Harnessing nature: Biological systems, such as using aquatic plants and filters, may offer some nutrient reduction, but their effectiveness varies. Wetlands require considerable land area and have not shown consistent success.
- Advanced technologies: Bioreactors offer superior treatment, but their high cost often makes them impractical for many farms.
The Cost-Efficiency Dilemma
A significant obstacle lies in treating large volumes of wastewater with relatively low nutrient concentrations. This renders advanced and highly efficient solutions, such as bioreactors, economically unfeasible.
Promising Paths for Sustainable Treatment
However, there is light at the end of the tunnel:
- Recirculating Aquaculture Systems (RAS): By concentrating nutrients, RAS systems make wastewater treatment with costly methods more efficient.
- Biofloc Technology: This innovative approach uses natural processes within the pond to convert waste into a supplemental food source for animals while reducing nutrient levels.
By embracing these advancements, we can ensure that aquaculture remains a sustainable food source for future generations.
The Road Ahead: A Multifaceted Approach
While advances in treatment technologies are promising, achieving sustainable aquaculture requires a multifaceted approach:
- Improved feed management: Minimizing waste through efficient feeding practices and food usage is crucial.
- Integrated systems: Combining different treatment methods may be necessary for optimal results.
- System redesign: Modifications to aquaculture systems themselves may be needed to create more efficient nutrient management.
Conclusion
Aquaculture plays a vital role in global food security. By employing responsible practices and innovative technologies to manage nutrient loads, we can achieve both increased production and environmental protection, ensuring a healthy planet and a secure food supply.
The study was funded by the Queensland Department of Environment and Science and Griffith University.
Contact
Michele A. Burford
Griffith University
Meadowbrook, QLD 4131, Australia.
Email: m.burford@griffith.edu.au
Reference (open access)
Tabrett, S., Ramsay, I., Paterson, B., & Burford, M. A. 2024. A review of the benefits and limitations of waste nutrient treatment in aquaculture pond facilities. Reviews in Aquaculture. https://doi.org/10.1111/raq.12921
