The use of renewable energy to improve the sustainability of Southeastern U.S. pond aquaculture: technical, economic, and industry evaluations of solar power options

The purpose of this planning project is to form collaborations between the stakeholders in the pond aquaculture industry—farmers, processors, industry officials, extension agents, university and government researchers, equipment manufacturers, and electricity providers—to develop full proposals to examine the scientific and economic feasibility of using renewable energy water circulation technologies to improve the sustainability of aquacultural operations. Pond aquaculture in the Southeastern U.S., primary the catfish industry, is profitable but may not be considered sustainable because it requires large inputs of feeds, chemicals, and energy. One recommendation to improve sustainability is to control and minimize electrical aeration use, and technologies that could use renewable energy have shown a potential to be utilized towards that effort (Boyd and Tucker 1995; Tucker and Steeby 1995; Green 2004). The full proposal would leverage ongoing and completed research to develop the experimental, field, and economic studies needed to examine the potential impacts of renewable energy water circulation technology use on aquaculture sustainability.

The sustainability of pond aquaculture, primarily catfish farming, has been a significant topic of study. Boyd and Tucker (1995) assessed the sustainability of channel catfish farming by examining all aspects of production from pond construction to effluent management. They stated that, “since channel catfish farming requires large inputs of feeds, chemicals, and energy, it cannot be considered truly sustainable because it diminishes resource bases”. Ten recommendations were made for improving sustainability; one was that “aeration should be provided, but aerators should be operated only when dissolved oxygen concentrations decline”. Boyd (1999) examined aquaculture sustainability and environmental issues, relaying the results of studies that found that, overall, catfish farming was a “green industry”. Boyd concluded, however, that, “there is urgency for the assessment of environmental impacts of aquaculture so that better management practices can be developed to prevent or mitigate these impacts”.

The use of water circulators in pond aquaculture may be a strategy to address both energy use and environmental (effluent) concerns. Boyd (1998) described the greatest influence of water circulators as “the blending of surface water with subsurface water”. He stated that “water circulation prevents thermal and chemical destratification”, “helps maintain oxygenated conditions at the mud-water interface”, and “stimulates phytoplankton growth” as it establishes a uniform dissolved oxygen profile. Gross et al. (2000) examined nitrogen transformation and balance in channel catfish ponds and noted the environmental benefits of water circulation. They concluded that “water circulation can enhance the rate of nitrification and convert potentially toxic NH3 [ammonia] to NO3 [nitrate] and enhance losses of nitrogen by providing more NO3 for denitrification” as well as “favor NH3 loss from the water via diffusion”. They also conclude that water circulation “will suspend organic matter from the sediment in the water column and the more oxygenated environment in the water as compared to the bottom soil should result in faster organic matter decomposition and less accumulation of organic matter on pond bottoms” (Gross et al. 2000). This is conclusion is particularly significant because Boyd (1999) stated that the ”total suspended solids was the only water quality variable often outside of the normal concentration limits for typical National Pollution Discharge Elimination System (NPDES) permits for effluents” and that one of the three main sources was the erosion of pond bottoms.

Several researchers have evaluated water circulators in aquaculture. Most notably, Howerton et al. (1994) designed a horizontal, axial-flow water circulator for use in channel catfish ponds. Tucker and Steeby (1995) evaluated this water circulator, finding “impressive” reductions in electrical aerator use. In their comparison of aeration requirements between uncirculated control and circulated ponds, they found 456 hours and 265 hours, respectively. These results translated into an overall power use per pond of 6840 kWh for the uncirculated ponds and 3975 kWh for the circulated ponds, a reduction of 42%. The power savings, however, were “substantially offset” by the electrical costs of circulation at 2169 kWh. Howerton et al. (1994) concluded that “although several studies have shown benefits of water circulation, the value of water circulation and the best methods of applying water circulation are not known, and further testing by researchers and “on farm” evaluation by commercial producers is necessary.

These findings have prompted several studies on renewable energy water circulators. Green (2004) at the USDA-ARS Aquaculture Systems Research Unit is evaluating pond-level mechanical methodologies to manage phytoplankton in catfish production ponds. The study will examine several circulators, including a solar powered propeller circulator manufactured by Pump Systems Inc. that is a smaller version of models normally used for lake destratification and wastewater treatment. The unit can circulate up to 2 hectares (5 acres) of water, however, the unit at a cost of $13,000 may not be economically sustainable. Similarly, the principal investigators at Tuskegee University are currently evaluating several solar powered diffused-air circulators at the pilot scale for water circulation and flow rate capabilities. Though the use of diffused air may be the least efficient at aeration (Boyd 1998), it is very capable at moving water. Diffused-air aerators have been proven to be effective for thermal and chemical destratification in large bodies of water (Mackay et al 2003). These units, manufactured by Kelln Solar for livestock-watering dugout aeration, may have lesser capabilities, but cost less than $5,000.

The project generated from this planning project would have the overall goal of finding cost and technically efficient ways of incorporating water circulation technologies into pond aquaculture production. The goal of this planning proposal focuses on moving existing pond aquaculture systems toward sustainable aquaculture. The planning grant will result in the development of a full proposal that is research-based with an educational outreach component to extend the project findings to the public. The full proposal will include pilot, experimental, field scale, and economic evaluations of the capabilities of several solar-powered circulation systems. The field scale evaluations will act as demonstrations of the technologies at actual operating farms, and the ecological and economic benefits to the farmer will be assessed, documented, and shared with our extension collaborators. This project is complementary to other SARE-funded projects in improving of the sustainability of aquaculture, such as those that have examined the management of effluents (OS04-018, SW01-062, FNE00-330, FW00-104, etc.). A Planning Grant is applied for because we wish to plan for the submission of a Research & Education proposal, gain commitments from cooperating institutions and the participation of end-users.