Bacterial, viral, and parasitic disease outbreaks have severely impacted shrimp production over the last thirty years, leading to ongoing modifications to farming practices. While most shrimp are still produced in extensive or semi-intensive (high volume, low density) ponds, there is recognition of and movement toward intensive (low volume, high density) techniques to achieve production goals (Villarreal & Juarez, 2022) and reduce per unit carbon emissions. However, with intensification comes increased waste production, which, if not appropriately managed, can contribute to significant problems in the production system and the surrounding environment, ultimately leading to a recurring disease cycle. Control and management of waste solids in ponds and tanks are essential for improving production outcomes and reducing the environmental impact of this farming practice. Engineered solutions to control waste solids, like self-cleaning tanks, are used in intensive land-based finfish aquaculture operations to enhance rearing conditions. Applying this technology to intensive shrimp production is promising; however, there is a need to establish and understand key technical and biological parameters that impact the feasibility, operation, and, ultimately, the performance of self-cleaning tanks and small-scale ponds for shrimp.
The impact of key design parameters on intensive shrimp tank self-cleaning and mixing was evaluated using computational fluid dynamic modeling (CFD). Model results for water velocity magnitude and direction we re the major factors evaluated for performance. Water velocity magnitude data wa s assessed relative to literature values for shrimp swimming capacity. Velocities greater than 25–30 cm/s we re considered excessive for shrimp; velocities less than 10–15 cm/s were considered too low to move waste solids toward a central drain adequately.
Major findings point to the potential of using an independent method to create the radial current that carries waste solids to the center drain, separate from the primary rotating flow. In finfish aquaculture applications, a tank’s primary rotating flow creates the secondary radial current for self-cleaning with an appropriate center drain hydraulic loading rate. However, tanks used in shrimp aquaculture have significant differences in design and operation. Major differences include lower tank diameter-to-depth ratios, longer hydraulic retention times, and processes for aeration and oxygenation. These design and operational differences increase the difficulty of relying on the primary rotating flow to create self-cleaning conditions. The results of this study highlight this difficulty and propose a potential solution by utilizing a separate method that creates and/or enhances the radial current needed. The proposed solution of a pipe around the tank perimeter with water jets flowing towards the tank center drain combined with a method that creates a primary rotating flow resulted in the highest proportion of the tank bottom velocities in the ideal range of 15–25 cm/sec for self-cleaning.