12 JUNE 2014 • WORLD AQUACULTURE • WWW.WAS.ORG The Partitioned Aquaculture System David E. Brune My involvement with the partitioned pond concept consisted of experiences and interactions with a number of engineers, aquaculturists and producers over 30 years. As an assistant professor of Aquacultural Engineering, beginning in 1978 at the University of California, Davis, I became aware of William Oswald’s work at Berkeley with a “high-rate algal pond” for municipal wastewater treatment. His work stimulated my thinking about using photosynthetic systems to treat aquaculture wastewater. In 1980 Benard Colvin visited Davis, where he presented a seminar on his experiences with the Puerto Peñasco (Mexico) shrimp culture project. The culture system at Puerto Peñasco consisted of small raceways for growing penaeid shrimp at annual yields equivalent to 10 to 20 t/ha. At the time, typical fish and shellfish aquaculture annual yields from ponds were roughly 2 to 4 t/ha. The increased production potential was made possible by pumping clean seawater from shallow saline wells into raceways at rates needed to maintain good water quality. Water exiting the raceways was discharged to sandy lagoons, ultimately seeping into the Gulf of California. Obviously, such discharge would not be a sustainable practice on a larger scale. At this point I first got the notion to combine shrimp or fish raceway culture with Oswald’s high-rate pond for water treatment and reuse. By 1982 I had moved to Pennsylvania State University, where I worked on a variety of wastewater-treatment system designs. I was interested in exploring fish culture integrated with some kind of zero-discharge water treatment. Working with students in the Penn State Agricultural Engineering and the Environmental Resource Management departments, I developed a new design for a rotating biological contactor that we installed in a greenhouseenclosed trout raceway located at the Northeast Fisheries Center in Lamar, Pennsylvania. We successfully demonstrated zerodischarge trout culture using this bacterial technique, but it was obvious that capital and operating costs of these systems could not compete with conventional flow-through raceway aquaculture. In 1987, I relocated to Clemson University in South Carolina and installed the first operating system fully utilizing algal growth as the basis of aquaculture waste treatment. I called this approach the “Partitioned Aquaculture System,” or PAS, because it consisted of separating, or partitioning, raceway fish culture (requiring only 5 percent of water surface area) from the algal-driven water-treatment process. Initial work was targeted at reducing an environmental impact of aquaculture by reducing or eliminating discharge of pond effluent to public waters (Brune et al. 1999). The PAS Concept Optimizing a photosynthetically supported fish-culture system required a radical departure from traditional pond design. Because fish need only a small portion of the pond area to live and grow, the system could use raceways to confine animals so they would be easy to feed, harvest and protect from predators. Also, by confining fish at high density, they became the dominate consumers of dissolved oxygen in the raceway, making localized aeration in the raceway more cost-effective than in traditional ponds where the standing crop of fish often represents less than 25 percent of the total oxygen demand. Raceways were coupled to a high-rate algal pond, optimized for algal productivity (Brune et al. 2003, 2004). Maintaining high algal productivity rates, while simultaneously stabilizing algal density and controlling algal species composition, are the keys to greater aquaculture production in the PAS compared to traditional ponds. Pond aquaculture production is ultimately limited by the rate at which ammonia and carbon dioxide—two potentially toxic byproducts of aquatic animal metabolism—are removed from the system. In outdoor systems, phytoplankton remove ammonia and carbon dioxide from water to support algal growth. The waste-treatment capacity of ponds (and therefore the upper limits on fish or shrimp production potential) can be increased by improving conditions for algal growth because carbon dioxide and ammonia assimilation rates are proportional to phytoplankton productivity. Net primary productivity depends on water temperature, LEFT, FIGURE 3. The first four, 100-m2 prototype PAS units installed at in 1989 at Clemson University. The slow-rotating paddlewheel circulated water through the fishholding raceways on the right and the algal basin on the left. RIGHT, FIGURE 4. Six, 0.13-ha PAS units installed 1994 at Clemson University.
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