Bioflocs technology : an integrated system for the removal of nutrients and simultaneous production of feed in aquaculture

Future development of intensive aquaculture must deal with its impacts on the environment in the form of water pollution and the use of fish oil and fish meal. The bioflocs technology simultaneously addresses both problems co-occurring with the further expansion of the industry. While maintaining good water quality within the aquaculture systems it produces additional feed for the cultured animals. In contrast to conventional water quality control techniques, the bioflocs technology offers a sustainable, economical and easy-to-implement alternative. Chapter 1 gives an overview of the literature concerning nitrogen removal techniques in aquaculture and bioflocs technology. In Chapter 2, the impact of the carbon source on the performance of biofloc reactors was studied. The carbon source influenced the capacity of the technique to control the water quality in the biofloc reactors and the nutritional properties of the flocs. The carbon source also affected the eukaryotic and prokaryotic community composition of the bioflocs, which offers great possibilities for fine-tuning of the technique, more specifically concerning water quality control, feed production and/or costs. This prime importance of the choice of carbon source was confirmed in two further studies (Chapter 3 and Chapter 4) in which bioflocs grown on different substrates were fed to giant freshwater prawn (Macrobrachium rosenbergii) postlarvae and white shrimp (Litopenaeus vannamei), respectively. In both studies, glycerol-grown bioflocs showed better results than glucose-grown bioflocs. The potential significance of these results calls for further studies on the use of bioflocs as a feed in aquaculture, both in freshwater and saline systems. Parameters to consider in the future are accessibility, palatability or attractiveness of the bioflocs towards the animals, amino acid composition, essential fatty acids content and cost of the used carbon source as well as the overall cost of the technology (especially compared to conventional biofilter systems and feeding costs). In addition to the environmental, economical and sustainable considerations addressed above, a more specific problem was studied in Chapter 5, where aquaculture animals are exposed to lower temperatures during winter, possibly leading to mass mortality in industrial ponds. Covering the ponds with either plastic sheets or glass allowed solar heating of the culture water (thereby reducing the temperature decrease) and permitted to minimize water exchange. The application of bioflocs technology resulted in maintenance of good water quality, concomitantly providing additional feed to the animals, tilapia (Oreochromis niloticus x Oreochromis aureus) without compromising survival, growth and condition factor of the cultured species. At this moment, the aquaculture industry is most importantly faced with mass mortalities due to infectious diseases. To conclude this work, a potential extra added value feature of the bioflocs technology was studied in Chapter 6. In this study, bioflocs were found to be able to protect brine shrimp (Artemia franciscana) larvae from pathogenic Vibrio harveyi. These results indicate that in addition to water quality control and extra in situ feed production, the technique also has potential to protect the cultured animals from infections with pathogenic bacteria, which are responsible for major economic losses in aquaculture. To conclude, the last chapter (Chapter 7) provides a brief discussion of the performed studies. Directions for future in depth studies are raised based on the studies performed in this work that might contribute to further sustainable development of aquaculture

Primary Nutritional Content of Bio-Flocs Cultured with Different Organic Carbon Sources and Salinity

Application of bio-flocs technology (BFT) in aquaculture offers a solution to avoid environmental impact of high nutrient discharges and to reduce the use of artificial feed. In BFT, excess of nutrients in aquaculture systems are converted into microbial biomass, which can be consumed by the cultured animals as a food source. In this experiment, upconcentrated pond water obtained from the drum filter of a freshwater tilapia farm was used for bio-flocs reactors. Two carbon sources, sugar and glycerol, were used as the first variable, and two different levels of salinity, 0 and 30 ppt, were used as the second variable. Bio-flocs with glycerol as a carbon source had higher total n-6 PUFAs (19.1 + 2.1 and 22.3 + 8.6 mg/g DW at 0 and 30 ppt, respectively) than that of glucose (4.0 + 0.1 and 12.6 + 2.5 mg/g DW at 0 and 30 ppt). However, there was no effect of carbon source or salinity on crude protein, lipid, and total n-3 PUFAs contents of the bio-flocs

The application of bioflocs technology to protect brine shrimp (Artemia franciscana) from pathogenic vibrio harveyi

Aims: To study the potential biocontrol activity of bioflocs technology. Methods and Results: Glycerol-grown bioflocs were investigated for their antimicrobial and antipathogenic properties against the opportunistic pathogen Vibrio harveyi. The bioflocs did not produce growth-inhibitory substances. However, bioflocs and biofloc supernatants decreased quorum sensing-regulated bioluminescence of V. harveyi. This suggested that the bioflocs had biocontrol activity against this pathogen because quorum sensing regulates virulence of vibrios towards different hosts. Interestingly, the addition of live bioflocs significantly increased the survival of gnotobiotic brine shrimp (Artemia franciscana) larvae challenged to V. harveyi. Conclusions: Bioflocs grown on glycerol as carbon source inhibit quorum sensing-regulated bioluminescence in V. harveyi and protect brine shrimp larvae from vibriosis. Significance and Impact of the Study: The results presented in this study indicate that in addition to water quality control and in situ feed production, bioflocs technology could help in controlling bacterial infections within the aquaculture pond

The effect of different carbon sources on the nutritional value of bioflocs, a feed for Macrobrachium rosenbergii postlarvae

A 15-day lab-scale experiment was performed to determine the possible use of bioflocs as a feed for Macrobrachium rosenbergii postlarvae. The bioflocs were grown on acetate, glycerol and glucose. A glycerol-fed reactor was initially inoculated with a Bacillus spores mixture. The highest protein content was obtained in the (glycerol+Bacillus) bioflocs, i.e. 58 +/- 9% dry weight (DW). The glycerol and acetate bioflocs showed a lower, but similar content (42-43% DW) and glucose bioflocs contained 28 +/- 3% DW. Higher total n-6 fatty acid contents were observed in the glycerol and (glycerol+Bacillus) bioflocs. The vitamin C content was variable, up to 54 mu g ascorbic acid g-1 DW in the glycerol bioflocs. Bioflocs were fed to M. rosenbergii postlarvae as the sole feed. High survival levels were obtained in the (glycerol+Bacillus) and glucose groups, i.e. 75 +/- 7% and 70 +/- 0% respectively. This was significantly higher than the starvation control (0% survival after 15 days). This indicated that the prawns were able to feed on the bioflocs. These results are in accordance with the biofloc's nutritional parameters and suggest that the choice of the carbon source used for growing bioflocs is of prime importance

Quorum Sensing-Disrupting Brominated Furanones Protect the Gnotobiotic Brine Shrimp Artemia franciscana from Pathogenic Vibrio harveyi, Vibrio campbellii, and Vibrio parahaemolyticus Isolates

Autoinducer 2 (AI-2) quorum sensing was shown before to regulate the virulence of Vibrio harveyi towards the brine shrimp Artemia franciscana. In this study, several different pathogenic V. harveyi, Vibrio campbellii, and Vibrio parahaemolyticus isolates were shown to produce AI-2. Furthermore, disruption of AI-2 quorum sensing by a natural and a synthetic brominated furanone protected gnotobiotic Artemia from the pathogenic isolates in in vivo challenge tests

Combining biocatalyzed electrolysis with anaerobic digestion

Biocatalyzed electrolysis is a microbial fuel cell based technology for the generation of hydrogen gas and other reduced products out of electron donors. Examples of electron donors are acetate and wastewater. An external power supply can support the process and therefore circumvent thermodynamical constraints that normally render the generation of compounds such as hydrogen unlikely. We have investigated the possibility of biocatalyzed electrolysis for the generation of methane. The cathodically produced hydrogen could be converted into methane at a ratio of 0.41 mole methane mole acetate, at temperatures of 22 ± 2°C. The anodic oxidation of acetate was not hampered by ammonium concentrations up to 5gNL. An overview is given of potential applications for biocatalyzed electrolysis