WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2014 19 (CONTINUED ON PAGE 20) ideal water quality conditions to a mean harvest size of 4.3 kg by 22 months post-hatch and a mean harvest size of 5.6 kg by 27 months post-hatch. Feed conversion during the production trial averaged 1.07 and, importantly, no major negative fish health events occurred (no viruses, sea lice, or kudoa parasites) despite zero employment of vaccines, formalin, antibiotics, or pesticides. Overall mortality accounted for about 7% of the population during the grow-out production phase, which included fish culled due to fungus. These studies suggest it is technically and biologically feasible to raise Atlantic salmon to food-size in closed-containment systems, even in freshwater at locations remote from the ocean. Eliminating Off-Flavor from Fish Produced in Closed-Containment Systems Two presentations described technologies and practices to eliminate earthy/musty off-flavors sometimes encountered in RAS-produced fish. Niels Jorgensen (University of Copenhagen, Denmark) presented procedures for reduction of off-flavors caused by MIB and geosmin in rainbow trout from RAS in Denmark. John Davidson (TCFFI, USA) reported on three studies examining depuration procedures to mitigate off-flavor from harvest-size Atlantic salmon. The depuration process for these fish was optimized by using standard operating procedures that provided clean and relatively biofilm-free systems during a 7 to 14-d depuration period. Biofilter media should not be used within depuration systems due to off-flavor bacteria and compounds present in associated biofilms. In addition, pre-disinfection of depuration systems using 250 mg/L H2O2 appears to enhance offflavor removal. Denitrification and Microbiology in Closed-Containment Systems Four presentations focused on the water quality issues of denitrification and microbiology within land-based closedcontainment systems. Lars-Flemming Pedersen (DTU Aqua, Denmark) opened the session with a discussion of microbial interactions (particularly nitrifying bacteria) with RAS water quality. The session then shifted towards denitrification with Keiko Saito (University of Maryland, USA) describing anaerobic waste treatment to remove nitrate and biosolids within zero-flushing land-based closed-containment systems for marine warm-water species. Likewise, Jaap van Rijn (Hebrew University of Jerusalem, Israel) described the importance of an anaerobic treatment stage for removing nitrate, phosphate, and off-flavor compounds. Both scientists described actual facilities that use innovative technologies to operate with practically no water flushing or waste discharge. Although they presented different technologies, both scientists described processes used to digest and hydrolyze biosolids (i.e., manure, waste feed, sloughed biofilm) within the RAS to generate organic acids that serve as a carbon source to fuel heterotrophic denitrification. These technologies mitigate nitrate accumulation without flushing the system with new makeup water. Dr. Saito also described how the University of Maryland process could be used to produce hydrogen sulfide to drive chemoautotrophic denitrification. Volumetrically the anaerobic digestion basin described by Jaap van Rijn might equal approximately 20 percent of the total RAS volume and, in addition to nitrate removal, phosphate is deposited within this basin largely as hydroxyapatite [Ca5(PO4)3(OH)]. Moreover, geosmin and MIB are strongly bound to the anaerobic sludge in the basin and the sludge’s internal biological activity removes these off-flavor compounds. In the final denitrification talk, Laura Christianson (TCFFI, USA) described nitrate removal using relatively low-cost and simple woodchip bioreactors. Such bioreactors have been used to treat agricultural tile drainage but are now being trialed for treatment of RAS discharge in TCFFI research funded by the USDA ARS and Tides Canada. The woodchips provide a surface area for the growth of heterotrophic bacteria that utilize the wood’s carbon to fuel denitrification. Assessment of Alternate Production Systems for Salmon Farming Brian Vinci (TCFFI, USA) and Trond Rosten (SINTEF, Norway) co-presented a comparative economic and environmental analysis of land-based versus net-pen salmon production for a 3,300 mt/y Atlantic salmon model production facility. This volume is approximately 1 percent of the Atlantic salmon consumed in the U.S. annually. The land-based system was based on grow-out trials conducted at TCFFI, whereas the net-pen model was based on conservative estimates using data sets from Norway and an investment plan for establishment of a 3,300 mt/y production (headon gutted; HOG) open pen facility (small-scale open-pen farm). Findings indicated the cost of production was approximately equal for land-based and net-pen production at US$ 4/kg of head-on gutted product. Fixed capital investments associated with building facilities were greater for the land-based system, but the required site license costs in Norway brought the overall costs of the two options more in line. The 10-year net present value analysis showed that rates of return were approximately equal (15 percent) under likely scenarios where land-based produced salmon achieved a price premium. A life cycle assessment indicated that land-based production would have a larger carbon footprint than net-pen production if the former were sited to use electricity provided by a typical US mix of fossil fuels. However, if fossil fuels are replaced with hydropower, the carbon footprints of the two production options were approximately equal. Net-pen salmon production in Scandinavia followed by airfreight export to the US had a slightly larger carbon footprint than land-based salmon production in the US using fossil fuels. The environmental value of escapee prevention, fish pathogen exclusion, and disease minimization was not quantified, but could potentially benefit a land-based system. It is likely that a variety of technologies, including hybrids of the options compared here, will be used in the future. Following this comparative analysis, Andrew King (University of Tasmania, Australia and University of St. Andrews, Scotland) presented an evaluation of production expansion options for the Tasmanian salmon industry. The use of land-based closedcontainment systems for at least a portion of the Tasmanian production period could reduce production costs and risks associated with existing production methods. Svein Martinsen (Nekton AS / Smola Hatchery and Smolt Farm, Norway) closed the session with an assessment of floating closed-containment Atlantic salmon farming systems. His company
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