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Biofloc technology (BFT) is considered the new 'blue revolution' in aquaculture (Stokstad 2010) since nutrients can be continuously recycled and reused in the culture medium, benefited by the in situ microorganism production and by the minimum or zero water exchange (Avnimelech 2015). These approaches might face some serious challenges in the sector such as competition for land and water and the effluents discharged to the environment which contain excess of organic matter, nitrogenous compounds and other toxic metabolites.
BFT was first developed in the early 1970s by the Aquacop team at Ifremer-COP (French Research Institute for Exploitation of the Sea, Oceanic Center of the Pacific) with different shrimp penaeid species including Litopenaeus vannamei, L. stylirostris and Penaeus monodon (Emerenciano et al. 2011). In the same period, Ralston Purina (a private US company) in connection with Aquacop applied the technology both in Crystal River (USA) and Tahiti, which lead to the greater understanding of the benefits of biofloc for shrimp culture. Several other studies enabled a comprehensive approach to BFT and researched the inter-relationships between water, animals and bacteria, comparing BFT with an 'external rumen' but now applied for shrimp. In the 1980s and at the beginning of the 1990s, both Israel and the USA (Waddell Mariculture Center) started R&D in BFT with Tilapia and Pacific white shrimp L. vannamei, respectively, in which environmental concerns, water limitation and land costs were the main causative agents that promoted the research (Emerenciano et al. 2013).
Fig. 12.5 Biofloc technology (BFT) applied for marine shrimp culture in Brazil (a) and for Tilapia culture in Mexico (b) (Source: EMA-FURG, Brazil and Maurício G. C. Emerenciano)
The first commercial BFT operations and probably the most famous commenced in the 1980s at the 'Sopomer' farm in Tahiti, French Polynesia, and in the early 2000s at the Belize Aquaculture farm or 'BAL', located in Belize, Central America. The yields obtained using 1000 msup2/sup concrete tanks and 1.6 ha lined grow-out ponds were approximately 20—25 ton/ha/year with two crops at Sopomer and 11—26 ton/ha/ cycle at BAL, respectively. More recently, BFT has been successfully expanded in large-scale shrimp farming in Asia, in South and Central America as well as in smallscale greenhouses in the USA, Europe and other areas. At least in one phase (e.g. nursery phase) BFT has been used with great success in México, Brazil, Ecuador and Peru. For commercial-scale Tilapia culture, farms in Mexico, Colombia and Israel are using BFT with productions around 7 to 30 kg/msup3/sup (Avnimelech 2015) (Fig. 12.5b). Additionally, this technology has been used (e.g. in Brazil and Colombia) to produce tilapia juveniles (~30 g) for further stock in cages or earthen ponds (Durigon et al. 2017). BFT has mainly been applied to shrimp culture and to some extent with tilapia. Other species have been tested and show promise, as noted for silver catfish (Rhamdia quelen) (Poli et al., 2015), carp (Zhao et al., 2014), piracanjuba (Brycon orbignyanus) (Sgnaulin et al., 2018), cachama (Colossoma macropomum) (Poleo et al., 2011) and other crustacean species such as Macrobrachium rosenbergii (Crab et al., 2010), Farfantepenaeus brasiliensis (Emerenciano et al., 2012), F. paulensis (Ballester et al., 2010), Penaeus semisulcatus (Megahed, 2010), L. stylirostris (Emerenciano et al., 2011) and P. monodon (Arnold et al., 2006). The interest in BFT is evident by the increasing number of universities and research centres carrying out research particularly in the key fields of grow-out management, nutrition, reproduction, microbial ecology, biotechnology and economics.
Microorganisms play a key role in BFT systems (Martinez-Cordoba et al. 2015). The maintenance of water quality, mainly by the control of the bacterial community over autotrophic microorganisms, is achieved using a high carbon to nitrogen ratio (C:N) since nitrogenous by-products can be easily taken up by heterotrophic bacteria. In the beginning of the culture cycles a high carbon to nitrogen ratio is required to guarantee optimum heterotrophic bacteria growth, using this energy for its maintenance and growth (Avnimelech 2015). Additionally, other microorganism groups are crucial in BFT systems. The chemoautotrophic bacterial community (i.e. nitrifying bacteria) stabilizes after approximately 20—40 days and might be responsible for two-thirds of the ammonia assimilation in the system (Emerenciano et al. 2017). Thus, the addition of external carbon should be reduced and alkalinity consumed by the microorganisms must be replaced by different carbonate/bicarbonate sources (Furtado et al. 2011). The stability of zero or minimal water exchange depends on the dynamic interaction amongst communities of bacteria, microalgae, fungi, protozoans, nematodes, rotifers, etc. that will occur naturally (MartinezCordoba et al. 2017). The aggregates (bioflocs) are a rich protein-lipid natural source of food that become available 24 h per day due to a complex interaction between organic matter, physical substrate and large range of microorganisms (Kuhn and Boardman 2008; Ray et al. 2010). The natural productivity in a form of microorganisms' production plays three major roles in the tanks, raceways or lined ponds: (1) in the maintenance of water quality, by the uptake of nitrogen compounds generating in situ microbial protein; (2) in nutrition, increasing culture feasibility by reducing feed conversion ratios and a decrease in feed costs; and (3) in competition with pathogens (Emerenciano et al. 2013).
Regarding the water quality for the culture organisms, besides oxygen, excess of particulate organic matter and toxic nitrogen compounds are the major concern in the biofloc systems. In this context, three pathways occur for the removal of ammonia nitrogen: at a lesser rate (1) photoautotrophic removal by algae and at a higher rate (2) heterotrophic bacterial conversion of ammonia nitrogen directly to microbial biomass and (3) autotrophic bacterial conversion from ammonia to nitrate (MartinezCordoba et al. 2015). The nitrate available in the systems plus other minor and major nutrients accumulated over the cycle could be used as substrate for plant growth in aquaponic systems (Pinho et al. 2017).
The application of BFT in aquaponic systems is relatively new, although Rakocy (2012) mentions a commercial pilot-scale project with tilapia. Table 12.2 summarizes key recent studies that have used BFT in aquaponic systems.
Overall, the results demonstrate that biofloc technology can be used and integrated in a fish or shrimp-plant production. BFT when compared to other conventional aquaculture systems (such as RAS) actually improved the plant and fish yields and promoted better plant visual quality (Pinho et al. 2017), but not in all cases (Rahman 2010; Pinho 2018). Pinho et al. (2017) observed that lettuce yields with the BFT system were greater compared to the clear-water recirculation system (Fig. 12.6). This is possibly due to the higher nutrient availability provided by the
Table 12.2 Recent studies around the world applying the BFT in aquaponic systems for different aquatic and plant species
table thead tr class="header" thAquatic species/th th Plant species /th th Main results /th th References /th /tr /thead tbody tr class="odd" tdTilapia/td td Lettuce /td td Biofloc technology did not improve lettuce production as compared to conventional hydroponic solution /td td Rahman (2010) /td /tr tr class="even" tdTilapia/td td Lettuce /td td Yield and visual quality of lettuce was improved using BFT as compared to clear-water recirculation system /td td Pinho et al. (2017) /td /tr tr class="odd" tdTilapia (nursery)/td td Lettuce /td td Plant performance (lettuce) using Tilapia in a nursery phase (1–30 g) was negatively influenced by biofloc wastewater as compared to RAS wastewater after two plant cycles (13 days each). Plant visual aspects were better in RAS as compared to BFT /td td Pinho (2018) /td /tr tr class="even" tdTilapia/td td Lettuce /td td The presence of filtering elements (mechanical filter and biological filter) positively affected the lettuce production in aquaponic systems as compared to treatment without filters using BFT /td td Barbosa (2017) /td /tr tr class="odd" tdTilapia/td td Lettuce /td td Low salinity (3 ppt) can be performed in aquaponics using BFT. Visual and performance parameters indicated that the purple variety had better performance than the smooth and crisped varieties /td td Lenz et al. (2017) /td /tr tr class="even" tdSilver catfish/td td Lettuce /td td The use of bioflocs in the aquaponic system may improve the productivity of lettuce in an integrated culture with silver catfish /td td Rocha et al. (2017) /td /tr tr class="odd" tdiLitopenaeus vannamei/i/td td iSarcocornia ambigua/i /td td The performance of marine ishrimp L. vannamei/i was not affected by the iS. ambigua/i integrated aquaponics production and also improve the use of nutrients (e.g. nitrogen) in the culture system /td td Pinheiro et al. (2017) /td /tr /tbody /table
Fig. 12.6 Experimental aquaponics greenhouse comparing biofloc technology and RAS wastewater at Santa Catarina State University (UDESC), Brazil. (Source: Pinho et al. 2017)
higher microbial activity. However, this trend was not observed in the study by Rahman (2010), who compared effluent from fish culture in a BFT system to a conventional hydroponic solution in a lettuce production. In addition, Pinho
Fig. 12.7 High salinity halophyte Sarcocornia ambigua aquaponics production integrated with Pacific white shrimp Litopenaeus vannamei successfully applying biofloc technology at Santa Catarina Federal University (UFSC), Brazil. (Source: LCM-UFSC, Brazil)
Fig. 12.8 Aquaponics lettuce production integrated with Tilapia using biofloc technology (left) and accumulation of suspended solids in lettuce roots (right). Barbosa (2017)
(2018) in a recent study observed that productive performance of lettuce in aquaponic system using Tilapia in a nursery phase (1—30 g) was negatively influenced by biofloc wastewater as compared to RAS wastewater over 46 days. The variation in results identifies the need for additional studies in this area.
BFT can be used with low salinity water, e.g. with some varieties of lettuce (Lenz et al. 2017), and higher salinity waters can be used, e.g. with halophyte plant species such as Sarcocornia ambigua co-culture with Pacific white shrimp Litopenaeus vannamei (Pinheiro et al. 2017) (Fig. 12.7). Silver catfish Rhamdia quelen has also shown good potential for the integration of aquaponics with BFT (Rocha et al. 2017).
With BFT, the concentration of solids can severely affect the roots and impact nutrient absorption and oxygen availability. As a result, yields can be affected but also the visual quality of the plants (e.g. lettuces) which is an important criterion for consumers. With this in mind, solids management is an important subject for further studies where the impact of solids (particulate fraction and also dissolved fraction) in aquaponic systems when applying BFT is considered (Fig. 12.8). In addition, economic studies need to be undertaken to compare the costs involved of the various aquaculture and plant growing systems and to identify appropriateness relative to different locations and conditions.