66 June 2012 Book Review Biofloc Technology, Second Edition by Yoram Avnimelech John A. Hargreaves1 The 500 copies of the first edition of Biofloc Technology sold out quickly, necessitating a second edition of the book. Given how quickly things are moving in this field of inquiry, this decision seems warranted. Indeed the second edition includes many interesting new dimensions of biofloc technology. The editor of this book is Yoram Avnimelech, who has dedicated a large part of his lengthy career to the understanding of the dynamics of intensive pond systems. He has published many of the fundamental papers in this field and is eminently qualified to write authoritatively on the subject. The original book consists of chapters that describe the basics of biofloc technology. These include chapters on the three main microbial processes in biofloc systems; nitrogen (ammonia) control in biofloc systems; managing biofloc ponds, including aerator placement and recipes for carbohydrate supplementation; biofloc system start-up; and the nutritional value of bioflocs for tilapia and shrimp. The original book contains an abundance of practical information as well as the underlying mechanistic explanations for why biofloc systems work the way they do. The second edition is now 272 pages, nearly 50 percent more than the first edition. Whereas the first edition was written exclusively by Yoram Avnimelech, the second edition includes five new multi-authored chapters and these will be the focus of this review. David Kuhn is the lead author of a chapter on ex-situ biofloc technology. This refers to applications of biofloc technology to waste streams from recirculating or other intensive culture facilities. In this chapter, the use of biofloc technology in the form of sequencing batch reactors (SBRs) is described. Using SBRs can result in significant reductions in the mass discharge of waste solids. Managing SBRs in alternating aerobic and anaerobic modes results in digestion of solids and reduction of nitrate, a substance than accumulates in many intensive systems, including those managed with biofloc technology. Unfortunately the chapter does not include design criteria to allow the design of SBRs based on waste loading. The second part of this chapter explores the use of dried biosolids obtained from SBRs as a feed ingredient for shrimp. In general, dried biosolids have a favorable amino acid profile, with some lysine deficiency, but trials using diets with dried biosolids solids up to 30 percent inclusion result in good shrimp growth. Although the chapter presents a favorable view of the potential of using dried biosolids as a feed ingredient, it does not take a critical view of the practical aspects of large-scale feed manufacture using this promising ingredient. Most of the recent research with biofloc technology is associated with so-called super-intensive shrimp raceways, work that has been underway through the US Marine Shrimp Farming Consortium for at least two decades. Andrew Ray describes recent research in these intensive systems. The chapter has abundant information that is useful for the design and management of shrimp raceways. Producing 3-6 kg/m3 can be easily obtained and predictable production of 8-10 kg/m3 now seems within reach. The chapter has good information about tank designs and air-lift configurations. The control of solids concentration is discussed in some detail, including the need to incorporate a solids control device in the raceway system. Interestingly the trend seems to be to try to manage biofloc systems with progressively lower levels of solids concentration, while maintaining functionality with respect to ammonia control. A new chapter by Peter DeSchryver describes how biofloc morphology and nutritional composition can be manipulated. In particular, the roles of turbulent mixing (i.e., shear), dissolved oxygen concentration, and organic carbon source on floc structure, size, and composition are considered. The chapter concludes with an analysis of the potential economic benefit of the recovery by cultured animals of nutrients in natural flocs consumed as food. Maurício Emerenciano and colleagues provide a discussion of experience using biofloc technology to maintain shrimp broodstock. Using biofloc systems for shrimp broodstock is justified on the basis of improved biosecurity and better nutrition relative to conventional systems. Although the results of trials that compared the performance of shrimp broodstock in ponds, tanks, and biofloc systems suggest that there is some benefit to using the biofloc approach, it is difficult to see much advantage relative to conventional approaches. In particular, the authors warn that the concentration of settleable solids must be maintained at a fairly low level (15 mL/L) to avoid clogging shrimp gills. Perhaps the most valuable chapter in the book describes commercial field experiences. In the last decade, excitement (Continued onpage 68)
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