The shrimp aquaculture industry has experienced exponential growth in recent years. To meet the growing global demand, producers have opted to intensify their operations, transitioning from extensive systems to intensive and even super-intensive models. However, this intensification brings significant energy and environmental challenges.
A team of researchers from Can Tho University (Vietnam) published a scientific review presenting the latest advanced technologies used to improve aeration and wastewater treatment in shrimp aquaculture. Additionally, the study introduces a sustainable energy model being researched and developed for aeration and wastewater treatment in shrimp farms.
A Sea of Challenges
The intensification of shrimp farming to meet demand has led to a dramatic increase in water and energy consumption. Aeration systems, essential for maintaining shrimp life, are major electricity consumers. Furthermore, the discharge of nutrient-laden and contaminated wastewater poses serious risks to aquatic ecosystems.
Oxygen: An Essential Resource
Shrimp, like any aquatic organism, require oxygen to survive and grow. In culture ponds, the concentration of dissolved oxygen (DO) is a critical factor. Aeration systems work tirelessly to maintain adequate DO levels, but their operation involves high energy consumption.
Wastewater: A Time Bomb
Shrimp farms generate large volumes of nutrient-rich wastewater containing nitrogen and phosphorus. If not properly treated, this water can cause eutrophication, algae blooms, and death of aquatic organisms. Additionally, it contains antibiotics and other chemicals used in production, exacerbating contamination.
Current State of the Art in Aeration Systems
Aeration is the process of increasing dissolved oxygen (DO) levels in pond water. Atmospheric pressure is higher than that of pond water, which drives oxygen from the air into the water at the pond’s surface, circulating it over the water body as bubbles.
There are two main types of aeration used in shrimp aquaculture: natural aeration and artificial aeration.
Natural Aeration:
- During the day, DO levels increase due to photosynthesis by phytoplankton and aquatic plants.
- This process is usually insufficient for shrimp, which live in the lower and middle layers of the pond.
- Intensive shrimp farming has increased the demand for DO, making artificial aeration necessary.
Artificial Aeration:
- Enhances contact between water and air interfaces to increase oxygen mixing.
- Compensates for the respiration of cultured species and the decomposition of organic matter.
- Alleviates DO stratification in water columns through water circulation.
Types of Aerators
Aeration is crucial for high-density shrimp farming, and a fundamental aspect is determining the appropriate type and number of aerators. The study describes current aeration systems and their main characteristics.
- Splash Aerators:
- Use mechanical energy to break water into droplets.
- Examples include paddlewheel aerators, spiral aerators, pump sprayers, and vertical pumps.
- Paddlewheel aerators are the most effective surface aerators.
- Bubble Aerators:
- Release air bubbles into the water.
- Examples include diffuse aerators, propeller aspirators, and submersible aerators.
- Diffuse aerators are energy-efficient, reducing operating costs.
- Gravity Aerators:
- Increase the interfacial area between water and air by flowing water over steps.
- Examples include step cascade aerators, circular stepped cascade aerators, and circular pool stepped aerators.
- Circular pool stepped aerators have high aeration transfer rates and efficiency.
Energy Use in Shrimp Aquaculture Systems
Intensive aquaculture increases food production but also presents energy-related challenges. Rising energy prices can affect food security. Key factors affecting energy demand in aquaculture include the species being cultured, cultivation systems, scale, technology, and local conditions. Aeration systems are particularly energy-intensive, consuming around 90-95% of the total energy in shrimp farming operations. Electric motors are commonly used for their efficiency, reliability, and low maintenance. In remote or off-grid areas, diesel generators are often used.
Recent Advances in Aeration Systems
Energy-efficient Aeration:
- Strategies such as intermittent control and smart control reduce energy consumption.
- Design modifications improve aeration efficiency and lower costs.
New Aeration Technologies:
- New aerators, like impeller aerators, centrifugal water stirrers, and tube aeration devices, improve oxygenation while saving energy.
Integration of Renewable Energy
Renewable energy sources such as photovoltaic systems, wind energy, and biogas are being used to power aeration systems, reducing fossil fuel dependence and operating costs. Examples include standalone photovoltaic systems, floating photovoltaic systems, and hydrogen-powered workboats.
These advances aim to balance the optimal dissolved oxygen levels necessary for shrimp health and growth with energy efficiency and cost-effectiveness, contributing to the sustainability of aquaculture operations.
State of the Art in Wastewater Treatment in Shrimp Aquaculture
Shrimp aquaculture faces various waste management challenges, including suspended solids and chemicals that can affect water quality and environmental sustainability. Below, we explore waste sources in shrimp aquaculture systems and recent innovations in the industry’s wastewater treatment.
Sources of Waste in Shrimp Aquaculture Systems
Solid waste, primarily composed of uneaten feed and fecal matter, can significantly impact shrimp growth and aquaculture performance. Suspended solids (small particles carried by water) and sedimented solids (particles that sink to the bottom) pose significant risks to water quality and aquatic life if not properly managed. Suspended solids can reduce light availability, crucial for phytoplankton growth, thus affecting natural food sources for aquatic animals. Conventional methods for removing fine solids, such as coagulation and sedimentation, are effective in these cases.
Nutrient Overload
Excessive nutrient accumulation, especially nitrogen and phosphorus, can lead to algae blooms, negatively impacting shrimp aquaculture. The decomposition of organic matter produces ammonia and nitrites, which are harmful to fish. Ammonia oxidation produces nitrate, generally safe for most cultured species. However, overconcentration of nitrate and phosphorus can lead to eutrophication, severely affecting the aquatic ecosystem.
Chemical Use
Reducing chemical use in aquaculture is a significant step towards more sustainable practices. Modern aquaculture has strictly reduced dependence on chemicals used for prophylaxis, disease treatment, anesthetics, and antiparasitics. Excessive or inappropriate use of substances like salts and lime can contribute to contamination if not properly managed.
Recent Advances in Wastewater Treatment
Cavitation
Cavitation is an effective wastewater treatment method that does not require reagents or ultraviolet light. This method minimizes byproducts and can reduce contaminants in wastewater, destroying the cellular structure of bacteria and other microorganisms.
Nanomaterials
Nanomaterials, such as nano adsorbents and nanofiber-based membranes, are used to adsorb contaminants and significantly reduce the amount of nitrates and phosphates. Although this technology is emerging, it has shown high efficiency in removing small particles and contaminants in wastewater.
High Rate Algal Systems
High-rate algal systems are a practical and cost-effective technology that completely removes ammonium, nitrates, and phosphates, treating more than 80% of organic matter. Aquatic plants like Picochlorum maculatum are effective in absorbing these nutrients in shrimp wastewater treatment systems.
Thermophilic Aerobic Solid-state Fermentation
This innovative technique produces clean nutrients, including ammonium gases, which can be used to cultivate algae. It requires a deep understanding of biological requirements and local environmental conditions for effective implementation.
Biofloc Technology
Biofloc technology uses bacteria to improve water quality and shrimp growth. This biological approach helps remove ammonia, nitrates, and dissolved organic solids in recirculating aquaculture systems, increasing farmers’ yields and conserving water.
Conclusion
The study presents the following conclusions:
- Socioeconomic Impacts and Inadequate Management: Shrimp aquaculture has faced socioeconomic impacts due to inadequate management practices. This study reviews recent technologies in aeration and wastewater treatment management in the shrimp industry.
- Technological Modifications: Technological approaches to aeration and wastewater treatment systems in shrimp aquaculture have been continuously modified to address specific challenges. These modifications aim to improve energy efficiency and protect the environment.
- Integrated Technology: Integrating suitable technologies offers greater efficiency compared to standalone approaches. This integration promotes sustainability, enhances shrimp growth, protects surrounding ecosystems, and ensures compliance with discharge and water quality regulations.
- Proposed Hybrid System: A hybrid system combining an advanced aeration system with a multi-stage wastewater treatment system is proposed. This system can significantly reduce environmental footprint, minimize energy consumption, effectively manage water quality, and promote sustainable shrimp aquaculture development.
- Need for Optimization and Validation: Although the technology is promising, it has not yet reached maturity and requires further studies for effective optimization and validation. In the long term, the proposed sustainable energy model will be a significant advancement with the ultimate goal of achieving financial viability and environmental sustainability for the shrimp industry and aquaculture in general.
The study was funded by the Postdoctoral Scholarship Programme of the Vingroup Innovation Foundation (VINIF).
Reference (open access)
Nhut Tien Nguyen, Phuong Lan Tran-Nguyen, Tran Thi Bich Chau Vo; Advances in aeration and wastewater treatment in shrimp farming: emerging trends, current challenges, and future perspectives. AQUA – Water Infrastructure, Ecosystems and Society 1 May 2024; 73 (5): 902–916. doi: https://doi.org/10.2166/aqua.2024.328
