ARS | Publication request: Greenhouse gas emissions associated with direct energy inputs for a warmwater low-salinity recirculating aquaculture systems

Submitted to: Book of Abstracts Aquaculture America
Publication Type: Abstract
Publication Acceptance Date: September 12, 2008
Publication Date: N/A

Technical Abstract: Greenhouse gases (GHGs) are gases that trap heat in the atmosphere. These gases include carbon dioxide (CO2), methane (CH3), nitrous oxide (N2O), and fluorinated gases. Some of these gases occur naturally and some are created by human activities which can increase their concentrations. The most common method of GHG concentration increase is through the combustion of fossil fuel for electricity. CO2 is the predominant GHG in the atmosphere and often the focus of greenhouse gas emission discussion although N2O gas emissions have 300 times more heat trapping capabilities over a 100 year time period. In the state of Florida the governor has issued executive orders for the reduction of greenhouse gases emission levels. By 2050 electric utilities will need to reduce GHG emission to 80 percent of 1990 levels. State agencies and departments are targeted for a 40% reduction from current emission levels by 2025. Given the GHG emission reduction pressure from state and federal administrations a GHG assessment was undertaken of the current recirculating aquaculture systems in operation at the USDA Agricultural Research Service Sustainable Marine Aquaculture project on the Harbor Branch Oceanographic Institute campus in Fort Pierce, FL. The low-salinity recirculating aquaculture systems (RAS) that were evaluated for GHG emission range in system volume from 10 m3 to 45 m3. The rearing options in these systems include fingerling to juvenile production and juvenile to grow-out production. In the two juvenile culture RAS units, tank diameter is 1.52 m and the number of tanks in each system is nine and ten respectively. System components include UV sterilizers, centrifugal and propeller pumps swirl separators, polygeyser and moving bead biofilters, and foam fractionators. In the grow-out production RAS units, tank diameter is 3.05 m and the number of tanks in each of the eight RAS units is four. System components include drum filters, propeller-wash bead filters, moving bed biofilters, UV sterilizers, centrifugal and propeller pumps, degas and oxygenation towers, and oxygenation cones. The systems have been utilized for red drum, Florida pompano, hybrid striped bass, and cobia grow-out studies. The direct energy inputs of the RAS units utilized to determine the GHG emission levels in terms of metric tons of carbon dioxide produced include the energy to pump, treat, and transport the water in the systems. The intent is to be able to compare the different system treatment designs and operation in some form of sustainability perspective and develop a GHS Reduction scorecard for energy and water savings of the various RAS unit designs.