Submitted to: Environmental Best Management Practices for Aquaculture
Publication Type: Book / Chapter
Publication Acceptance Date: 5/29/2007
Publication Date: 2/8/2008
Citation: Summerfelt, S.T., Vinci, B.J. 2008. Better Management Practices for Recirculating Aquaculture Systems. In: Tucker, C.S., Hargreaves, J.A., editors. Environmental Best Management Practices for Aquaculture. Ames, IA: Blackwell Publishing. p. 389-426. Interpretive Summary:
Technical Abstract: Under the 2004 federal aquaculture effluent limitation guidelines (Federal Register 2004), recirculating aquaculture systems with an annual production exceeding 45,454 kg (100,000 pounds) are classified as concentrated aquatic animal production (CAAP) facilities and are required to obtain a National Pollution Discharge Elimination System (NPDES) permit before discharging wastes into waters of the United States. The NPDES permit is contingent upon development of a facility-specific best management practices (BMP) plan that specifies how the permittee will reduce discharge of potential pollutants. Discharges into sewers flowing into publicly owned treatment works are not covered under the 2004 aquaculture effluent limitation guidelines. The major facility-level environmental issues created by using recirculating systems are the point-source waste streams generated during culture. This is therefore the focus of this chapter. Two distinct waste streams may be produced: small, but concentrated, slurries of captured biosolids and, in some cases, more dilute but relatively larger volume system overflows. The volume of system overflow from recirculating systems is much smaller than that discharged from a typical flow-through fish culture system. Recirculating aquaculture systems are unique among the other production systems and, as such, they have a unique set of potential environmental impacts. For many recirculating aquaculture systems, the lack of direct hydraulic connectivity with the environment means that environmental issues that are critical in other systems -- such as fish escapes and disease transfer to wild stocks -- are easily controlled. Dealing with these point sources of waste requires capturing, transferring, storing, treating, or utilizing the concentrated waste biosolids and --sometimes -- the comparatively concentrated recirculating system overflow. Removing waste biosolids from all water flows as rapidly as possible is probably the best approach to minimizing release of phosphorus and organic matter to the environment, because these constituents leach rapidly from captured or thickening biosolids. The comparatively small overflow from recirculating systems may contain concentrated dissolved wastes that must also be treated before the effluent can legally be discharged. Fortunately, concentrating the dissolved wastes into a comparatively small production system overflow reduces the volume of wastewater to be treated and provides increased waste treatment efficiency. This significantly reduces the size and cost of on-site wastewater treatment. In fact, the waste-concentrating effect that is inherent in the design of recirculating systems can, in some instances, make it practical to discharge wastes directly to publicly owned treatment works.