February 15-18, 2009 Washington State Convention Center Seattle ...

34
ENERGY USE FOR MECHANICAL AERATION OF AQUACULTURE PONDS
Claude E. Boyd
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, AL 36849 USA
boydce1@auburn.edu
Pond culture of channel catfish and marine shrimp has followed similar patterns. Production was increased through use of
feeds, and resulting problems with low dissolved oxygen (DO) concentration were initially solved through water exchange
(shrimp) and application of emergency aeration with tractor-powered aerators (channel catfish). Floating, electric aerators were
found to allow better control over DO concentration and permit greater production. Mechanical aeration use has increased
steadily, and at some intensive farms, pond aeration rates are as high as 6 to 8 hp/ha for channel catfish and 18 to 24 hp/ha for
marine shrimp. Mechanical aerators for channel catfish farming are based on a highly-efficient design developed at Auburn
University, but shrimp farmers mostly use less efficient aerators. Moreover, aerators tend to be operated nearly continuously in
shrimp ponds, but mainly at night in channel catfish ponds. Typically, aerators are operated about 1,000 hr per crop in catfish
ponds and 2,000 hr per crop in shrimp ponds, and net production is around 8,000 kg/ha for channel catfish and 14,000 kg/ha for
shrimp. Energy input is approximately 4,500-6,000 kW•hr/ha (0.56 to 0.75 kW•hr/kg) for channel catfish and 27,000 to 36,000
kW•hr/ha (1.93 to 2.57 kW•hr/kg) for marine shrimp. Energy use for aeration in shrimp culture could be reduced by 25 to 50%
by use of more efficient aerators. It also might be possible to lessen energy use in shrimp culture by reducing aerator operation
when DO concentrations are near or above saturation between mid morning and mid afternoon. In both types of aquaculture,
and especially in shrimp culture, some farms are investigating the use of heterotrophic systems in which bacterial floc largely
replaces phytoplankton. Around 30 to 40 hp/ha of aeration are used in “floc” systems for shrimp, and production of 20,000 to
24,000 kg/ha or more per crop is possible. The energy requirement per unit of shrimp production using Asian-type paddlewheel
aerators in “floc” systems is about the same as in “green-water” systems.
In both “green water” and “floc” systems, wastes are oxidized in ponds, and this consumes a portion of the DO supplied by
aerators. A possible innovation would be to remove wastes from culture systems to lessen DO requirements, and oxidize waste
externally using less energy-intensive technology than mechanical aeration.