**5.2 Addition of carbohydrate**

For assimilating 1 mole of ammonia, 1.18 mole of carbohydrate is exhausted according to Eq. (6), which indicates that when 1 g of NH4 <sup>+</sup> exists in water, about 12 g of C6H12O6 should be added [10, 17]. This needs to supervise the ammonia concentration of water continuously, which is difficult to implement actually. Thus, a general manipulation is that carbon source is added only when ammonia concentration excesses 1 mg/L with the NH4 <sup>+</sup> to C6H12O6 ratio (w:w) of 1:12 [10, 17]. Of course, the content of carbohydrate contained in material used as carbon source should be determined.

Another way for addition of carbohydrate to improve the bio-reaction of route 3 is adjustment of the C:N in water in real time. For this purpose, the contents of nitrogen in water are determined actually, and then materials rich in carbon or carbohydrate are added to adjust C:N. However, in fact, many times, the adjustment of C:N is not based on the actual carbon and nitrogen concentrations. Alternatively, only when feedstuff is fed, carbon source is considered to add, and the weight for addition is calculated according to the nitrogen content in feedstuff with a C:N of 15:1 [13].

Many materials could be used as carbon source for BFT system, such as acetate [18], glycerol [18], dextrose [19–21], cassava meal [22], cellulose [23], corn flour [24, 25], glucose [18], molasses [26–28], tapioca [29], wheat flour [28, 30], rice flour [16, 30], wheat bran [25, 31], rice bran [20, 29], starch [28, 32], poly-βhydroxybutyrate (PHB) [33, 34], brewery residues [22], and sugar [32].

#### **5.3 Aeration**

The process of ammonia assimilation via heterotrophic microorganisms needs a huge number of oxygen, because of (1) oxygen consumption by respiration of blooming growth of bacteria and (2) oxidized fermentation of organic materials secreted by bacteria [17]. Thus, it is needed to usually equip a robust air blower to blow air into the water body to maintain a highly dissolved oxygen level in water [2], in general at least 5 mg/L [4]. In some cases, even pure oxygen is used for this purpose.

#### **5.4 Treatment of by-product**

A result induced by blooming growth of heterotrophic bacteria is substantial accumulation of suspended solids or bioflocs, one of the side effects of utilizing BFT. In a BFT system constructed by the author in the present article, bacteria secrete massive metabolic materials such as protein and polysaccharide, which could bond feeds, feces, debris, and other organic matters together, to become bioflocs and suspended in water under aeration condition (**Figures 2** and **3**). The author also found that sometimes the total suspended solid (TSS) content in BFT system would accumulate to above 800 mg/L (**Figure 3b**). That high level of TSS will be harmful to aquatic animals, which would lead to oxygen depletion, obstruction of fish or shrimp gills, and mortality due to asphyxiation [35]. Therefore, treatment of those accumulated TSS is an important operation for BFT [36].

There are three ways used for treating of TSS. The first one is in situ eaten by fish or shrimp as supplemental food [37, 38] which is also the most frequently used method. The second one is equipping a settling chamber to remove excessive solids [39]. And the last one is using separation systems for biofloc production and aquatic animal production, respectively, so that the increasing TSS produced in biofloc production system will not affect the growth of fish or shrimp raised in another system whose water quality should remain controlled by the former system. And for this purpose, four 10 m<sup>3</sup> composite tanks in general need to be fixed for water

*Productivity characteristics of biofloc volume and TSS in closed traditional system (a) and BFT system (b) over time. Biofloc volume is defined as the volume of sinkable matter in 1 l water placed into an Imhoff cone in 15 min. TSS is represented as the mass (mg) of dry matter in 1 l water after filtering with a 0.45 μl*

*Novel Biofloc Technology (BFT) for Ammonia Assimilation and Reuse in Aquaculture In Situ*

treatment of 12 tanks with a volume of 500 L per tank [40].

**Figure 2.**

**Figure 3.**

*membrane.*

**9**

*Sedimentation of biofloc in an Imhoff cone.*

*DOI: http://dx.doi.org/10.5772/intechopen.88993*

*Novel Biofloc Technology (BFT) for Ammonia Assimilation and Reuse in Aquaculture In Situ DOI: http://dx.doi.org/10.5772/intechopen.88993*

**Figure 2.** *Sedimentation of biofloc in an Imhoff cone.*

#### **Figure 3.**

**5.2 Addition of carbohydrate**

tration excesses 1 mg/L with the NH4

should be determined.

a C:N of 15:1 [13].

**5.3 Aeration**

purpose.

**8**

**5.4 Treatment of by-product**

For assimilating 1 mole of ammonia, 1.18 mole of carbohydrate is exhausted

12 g of C6H12O6 should be added [10, 17]. This needs to supervise the ammonia concentration of water continuously, which is difficult to implement actually. Thus, a general manipulation is that carbon source is added only when ammonia concen-

course, the content of carbohydrate contained in material used as carbon source

is adjustment of the C:N in water in real time. For this purpose, the contents of nitrogen in water are determined actually, and then materials rich in carbon or carbohydrate are added to adjust C:N. However, in fact, many times, the adjustment of C:N is not based on the actual carbon and nitrogen concentrations. Alternatively, only when feedstuff is fed, carbon source is considered to add, and the weight for addition is calculated according to the nitrogen content in feedstuff with

Another way for addition of carbohydrate to improve the bio-reaction of route 3

Many materials could be used as carbon source for BFT system, such as acetate [18], glycerol [18], dextrose [19–21], cassava meal [22], cellulose [23], corn flour [24, 25], glucose [18], molasses [26–28], tapioca [29], wheat flour [28, 30], rice flour [16, 30], wheat bran [25, 31], rice bran [20, 29], starch [28, 32], poly-βhydroxybutyrate (PHB) [33, 34], brewery residues [22], and sugar [32].

The process of ammonia assimilation via heterotrophic microorganisms needs a

A result induced by blooming growth of heterotrophic bacteria is substantial accumulation of suspended solids or bioflocs, one of the side effects of utilizing BFT. In a BFT system constructed by the author in the present article, bacteria secrete massive metabolic materials such as protein and polysaccharide, which could bond feeds, feces, debris, and other organic matters together, to become bioflocs and suspended in water under aeration condition (**Figures 2** and **3**). The author also found that sometimes the total suspended solid (TSS) content in BFT system would accumulate to above 800 mg/L (**Figure 3b**). That high level of TSS will be harmful to aquatic animals, which would lead to oxygen depletion, obstruction of fish or shrimp gills, and mortality due to asphyxiation [35]. Therefore, treatment of those accumulated TSS is an important operation for BFT [36].

There are three ways used for treating of TSS. The first one is in situ eaten by fish or shrimp as supplemental food [37, 38] which is also the most frequently used method. The second one is equipping a settling chamber to remove excessive solids [39]. And the last one is using separation systems for biofloc production and aquatic

huge number of oxygen, because of (1) oxygen consumption by respiration of blooming growth of bacteria and (2) oxidized fermentation of organic materials secreted by bacteria [17]. Thus, it is needed to usually equip a robust air blower to blow air into the water body to maintain a highly dissolved oxygen level in water [2], in general at least 5 mg/L [4]. In some cases, even pure oxygen is used for this

<sup>+</sup> exists in water, about

<sup>+</sup> to C6H12O6 ratio (w:w) of 1:12 [10, 17]. Of

according to Eq. (6), which indicates that when 1 g of NH4

*Emerging Technologies, Environment and Research for Sustainable Aquaculture*

*Productivity characteristics of biofloc volume and TSS in closed traditional system (a) and BFT system (b) over time. Biofloc volume is defined as the volume of sinkable matter in 1 l water placed into an Imhoff cone in 15 min. TSS is represented as the mass (mg) of dry matter in 1 l water after filtering with a 0.45 μl membrane.*

animal production, respectively, so that the increasing TSS produced in biofloc production system will not affect the growth of fish or shrimp raised in another system whose water quality should remain controlled by the former system. And for this purpose, four 10 m<sup>3</sup> composite tanks in general need to be fixed for water treatment of 12 tanks with a volume of 500 L per tank [40].

## **6. Management of dissolved oxygen and ammonia in BFT system**

#### **6.1 Dissolved oxygen level**

Although numerous amounts of oxygen will be consumed by respiration of a large number of flourishing heterotrophic bacteria, the author in this article supervised that the dissolved oxygen continuously sustained a high level in fact in a *L. vannamei* BFT system equipping air blower, such as root blower (**Figure 4**). In general, air blew into per minute with 1–5% of water volume is adequate to maintain a high dissolved oxygen level. For example, in a pond reserving 1000 m<sup>3</sup> water, the flow rate of root blower should be 10–50 m<sup>3</sup> /min.

#### **6.2 Ammonia assimilation efficiency**

The speed of ammonia assimilation in BFT system is very fast; Avnimelech [13] reported that ammonia added to water body with a final concentration of 10 mg/L disappeared over a period of about 2 h post addition of glucose as carbon source. The author of the present chapter found that in the BFT system culture *L. vannamei*, a low ammonia level averaging 0.78 mg/L lasted during the whole period of culture in water body (**Figure 5b**). Moreover, nitrite and nitrate concentrations would also be limited at low levels in this BFT system (**Figure 5b**). Conversely, in the control system without water exchange, the average ammonia concentration was up to 6.35 mg/L, which in turn resulted in a very high level of nitrite of 11.78 mg/L subsequently (**Figure 5a**). Consequently, a very high shrimp mortality rate of 70% was found in this control water body, very far higher than that of the BFT system without mortality over the whole experimental period of 70 d (data not shown). Cardona et al. [41] reported that the survival rate of *Litopenaeus stylirostris* was 27.2% higher in the BFT system than that of the conventional system with huge water exchange, which was also contributed to the good water quality represented by those low ammonia and nitrite levels.

**7. Approaches for reusing of biofloc as supplemental food**

and fresh food rich in protein for fish and shrimp.

**7.1 Three ways for food use of biofloc**

**Figure 5.**

*points.*

**11**

Treatment of suspended solids or bioflocs is one of the most important operations for using BFT. Usually, those solids or bioflocs are not removed just as a waste from water. In contrast, they are reused as a complemented food source for aquatic animals, especially omnivorous species such as shrimp and tilapia, in a system adopting BFT. During development of bioflocs, bacteria secrete protein and polysaccharide, which bond with feeds, feces, debris, and other organic matters together. Furthermore, the author of this article found that biofloc was also a nutritional resource that could attract zooplanktons to prey, such as protozoa, rotifers, nematodes, ciliates, and flagellates (**Figure 6**), which in turn provides live

*TAN, nitrite, and nitrate concentrations in closed traditional system (a) and BFT system (b) at different time*

*Novel Biofloc Technology (BFT) for Ammonia Assimilation and Reuse in Aquaculture In Situ*

*DOI: http://dx.doi.org/10.5772/intechopen.88993*

There are three ways for biofloc used as food in aquaculture currently: (i) as a complemented food for fish or shrimp in situ [42–45], (ii) as a gradient for feedstuff to replace fishmeal [46–49], and (iii) as a normal feed to replace partial artificial feedstuff [50–55]. In brief, fish and shrimp consume biofloc rich in microbe, phytoplankton, and zooplankton as a food directly. Because animals take biofloc as a vice food source, thus in fact the biofloc hunted by fish and shrimp is only a few

**Figure 4.** *Dissolved oxygen level in a BFT system over time.*

*Novel Biofloc Technology (BFT) for Ammonia Assimilation and Reuse in Aquaculture In Situ DOI: http://dx.doi.org/10.5772/intechopen.88993*

**Figure 5.** *TAN, nitrite, and nitrate concentrations in closed traditional system (a) and BFT system (b) at different time points.*

## **7. Approaches for reusing of biofloc as supplemental food**

Treatment of suspended solids or bioflocs is one of the most important operations for using BFT. Usually, those solids or bioflocs are not removed just as a waste from water. In contrast, they are reused as a complemented food source for aquatic animals, especially omnivorous species such as shrimp and tilapia, in a system adopting BFT. During development of bioflocs, bacteria secrete protein and polysaccharide, which bond with feeds, feces, debris, and other organic matters together. Furthermore, the author of this article found that biofloc was also a nutritional resource that could attract zooplanktons to prey, such as protozoa, rotifers, nematodes, ciliates, and flagellates (**Figure 6**), which in turn provides live and fresh food rich in protein for fish and shrimp.

#### **7.1 Three ways for food use of biofloc**

There are three ways for biofloc used as food in aquaculture currently: (i) as a complemented food for fish or shrimp in situ [42–45], (ii) as a gradient for feedstuff to replace fishmeal [46–49], and (iii) as a normal feed to replace partial artificial feedstuff [50–55]. In brief, fish and shrimp consume biofloc rich in microbe, phytoplankton, and zooplankton as a food directly. Because animals take biofloc as a vice food source, thus in fact the biofloc hunted by fish and shrimp is only a few

**6. Management of dissolved oxygen and ammonia in BFT system**

*Emerging Technologies, Environment and Research for Sustainable Aquaculture*

water, the flow rate of root blower should be 10–50 m<sup>3</sup>

**6.2 Ammonia assimilation efficiency**

nitrite levels.

**Figure 4.**

**10**

*Dissolved oxygen level in a BFT system over time.*

Although numerous amounts of oxygen will be consumed by respiration of a large number of flourishing heterotrophic bacteria, the author in this article supervised that the dissolved oxygen continuously sustained a high level in fact in a *L. vannamei* BFT system equipping air blower, such as root blower (**Figure 4**). In general, air blew into per minute with 1–5% of water volume is adequate to maintain a high dissolved oxygen level. For example, in a pond reserving 1000 m<sup>3</sup>

The speed of ammonia assimilation in BFT system is very fast; Avnimelech [13] reported that ammonia added to water body with a final concentration of 10 mg/L disappeared over a period of about 2 h post addition of glucose as carbon source. The author of the present chapter found that in the BFT system culture *L. vannamei*, a low ammonia level averaging 0.78 mg/L lasted during the whole period of culture in water body (**Figure 5b**). Moreover, nitrite and nitrate concentrations would also be limited at low levels in this BFT system (**Figure 5b**).

system than that of the conventional system with huge water exchange, which was also contributed to the good water quality represented by those low ammonia and

Conversely, in the control system without water exchange, the average ammonia concentration was up to 6.35 mg/L, which in turn resulted in a very high level of nitrite of 11.78 mg/L subsequently (**Figure 5a**). Consequently, a very high shrimp mortality rate of 70% was found in this control water body, very far higher than that of the BFT system without mortality over the whole experimental period of 70 d (data not shown). Cardona et al. [41] reported that the survival rate of *Litopenaeus stylirostris* was 27.2% higher in the BFT

/min.

**6.1 Dissolved oxygen level**

parts of the whole. In other words, most of the bioflocs remain in the water body, which may be an obstacle for growth of fish and shrimp. For alleviating the negative effect of biofloc on animal growth, excessive parts should be collected from water body and could be taken as an alternative protein source for preparing feedstuff. Even more, biofloc is fed to fish or shrimp as feedstuff directly due to its whole and high nutritional value.
