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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING PRODUCTION EFFICIENCY IN WARM WATER AQUACULTURE THROUGH WATER QUALITY MANAGEMENT

Location: Warmwater Aquaculture Research Unit

Title: Development and evaluation of a new aerator for the catfish industry

Authors
item Brown, Travis
item Torrans, Eugene

Submitted to: Catfish Farmers of America Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: December 26, 2011
Publication Date: N/A

Interpretive Summary: The catfish aquaculture industry currently relies primarily on rotary “agitating-type” surface splash aerators to aerate aquaculture ponds. Agitating-type aerators are generally powered with 10-hp (7.5-kW) electric motors and average industry usage is approximately 2.6 hp (1.9-kW) per acre. Paddle-wheel aerators are a common example of agitating-type aerators. While paddle-wheel aerators add significant amounts of oxygen to the water, they are required to mechanically move large amounts of water to be effective. While this is acceptable for routine operations, when the DO level drops to very low concentrations (as when a plankton bloom dies and decomposes), a paddle-wheel aerator will frequently not immediately produce a DO concentration high enough to keep affected fish alive. If a large number of portable (tractor-powered) aerators are not immediately brought in to assist with the emergency aeration, the affected fish will be severely stressed and may die. The need exists for a system and method for aerating aquaculture ponds that efficiently maintains a healthy aquaculture environment and is capable responding quickly to temporary conditions that cause low oxygen environments. Modifications to an existing “Power Tube” aerator began in 2010. The current invention, the “Power Tube Airlift” (PTA) comprises a method and apparatus that relies on an injection of pressurized air to create a hydrostatic imbalance (rather than a mechanical agitator) to circulate aquaculture pond water and thereby aerate the aquaculture pond. Aeration efficiency tests were conducted on the PTA at a variety of different sparger water depths (air injection points) and electric motor speeds (rpm) to determine standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE). Water velocity was also measured to determine water flow rate and pumping (water moving) efficiency. The highest efficiency observed thus far was obtained at a sparger water depth of 20 ft (6 m). Additionally, when pond DO concentrations were lowered to 0.0 ppm (mg/L) to simulate an emergency condition (pond crash), the outflow water from the PTA had DO concentrations of approximately 5.46 ppm. By means of concentrating the aeration effort into a smaller area of the pond, emergency aeration efficiency would likely exceed that of paddlewheel aerators. The PTA has fewer moving parts which will reduce the costs associated with repairs and maintenance. Additionally, improved efficiency would reduce the energy requirements (electrcity and fuel) required by the catfish industry. The addition of diffused air and/or pure oxygen into the water inflow side of the PTA should increase efficiencies and will also be evaluated. Some of the material discussed in this abstract comprises the subject matter of a patent application currently pending with the US Patent and Trademark Office.

Technical Abstract: Traditional paddle-wheel aerators have been used for supplemental and emergency aeration in the aquaculture industry for over 30 years but distribute a high volume of water which dilutes the aeration effort over the entire pond volume. Thus, a great deal of equipment and a large amount of power is required to prevent extended periods of low dissolved oxygen (DO) conditions. The need exists for a system and method for aerating aquaculture ponds that efficiently maintains a healthy aquaculture environment and is capable of responding quickly to low DO concentrations without expending unnecessary energy. A new aerator, known as the “Power Tube Airlift” (PTA), has been designed to concentrate DO into a relatively small zone of water in a pond while maintaining elevated DO concentrations for a large biomass of fish (Figure 1). This is accomplished through an injection of pressurized air through a sparger assembly to create a hydrostatic imbalance, rather than a mechanical agitator, to aerate and circulate pond water. Aeration efficiency tests were conducted on the PTA at a variety of different sparger water depths (air injection points) and electric motor speeds (rpm) to determine standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE). Water velocity was also measured to determine water flow rate and pumping (water moving) efficiency. The highest efficiency observed thus far was obtained at a sparger water depth of 20 ft (6 m). SOTR and SAE ranged from 10.6-24.5 lb O2/h (4.8-11.1 kg O2/h) and 2.1-3.3 lb O2/hp·h (1.3-2.0 kg O2/kW·h), respectively. Water flow rate and pumping efficiency ranged from 6,660-10,658 gpm (25,209-40,342 lpm) and 1,075-1,830 gpm/hp (5,454-9,287 lpm/kW), respectively. Additionally, when pond DO concentrations were lowered to 0.0 ppm (mg/L) to simulate an emergency condition (pond crash), the outflow water had DO concentrations of approximately 5.46 ppm with the addition of diffused air into the water inflow side (downcomer) of the PTA. By concentrating the aeration effort into a smaller area of the pond (i.e., smaller water volume), emergency aeration efficiency would likely exceed that of paddlewheel aerators. Fewer moving parts and improved efficiency would reduce the costs associated with repair and maintenance, and lower energy (electricity and fuel) consumption, respectively, for the catfish industry. The addition of diffused air and/or pure oxygen into the water inflow side of the PTA will continue to be evaluated for maximum efficiency. Production trials in commercial-scale ponds will begin in 2012. Some of the material discussed in this abstract comprises the subject matter of a patent application currently pending with the US Patent and Trademark Office.

Last Modified: 12/17/2014
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