BIOFLOC AQUACULTURE

KNOW- HOW OF BIOFLOC TECHNOLOGY, PART-1

December 21, 2020

439

KNOW- HOW OF BIOFLOC TECHNOLOGY PART-1

Compiled by Dr.M.Menaga ,Mr.M.Mohammed Faizullah ,
Dr.S.Athithan ,Dr.S.Balasundari

Biofloc Technology: A Secret Behind its Success

In the Indian Aquaculture context, ‘Biofloc Technology’ is one of the most heard technical term in the past one year and it is widely propagated by many stakeholders in the aquaculture sector. The reason behind its propagation is mainly because of its

Ecofriendly formulae to recycle and reuse the culture water
Farmers acceptance in terms of innovativeness and risk-taking attitude
Massive research & development efforts undertaken by the research institutes

Comprehensive definitions of Biofloc disseminated in various versions

Biofloc Technology is a ‘suspended growth system’ that depends on active phytoplankton biomass, filamentous and floc forming bacteria, microbial grazers and aggregates of living and dead particulate organic matter for water quality maintenance
BFT is essentially a water quality management technique to minimize water exchange
BFT is a minimal to zero water exchange system and the addition of a carbon substrate that is low in nitrogen were added to prevent the accumulation of nitrogen.
BFT involves stimulating the growth of bacteria to remove nitrogenous waste by increasing the carbon/nitrogen ratio, mostly by the addition of an organic carbon source.

History and development of Biofloc technology (BFT)

The origin of BFT could be traced to early 1970’s at French Research Institute for Exploration of the Sea, Oceanic Center of Pacific (Ifremer-COP; Emerenciano et al. 2012). These types of systems with active microbial suspensions through continuous water circulation system was used for culturing various penaeid species including Litopenaeus vannamei, L. stylirostris, Penaeus monodon and Fenneropenaeus merguiensis (Aquacop 1975; Sohier 1986; Emerenciano et al. 2013). Another early work on BFT was in connection with Aquacop which was done in both the Cryster
River (USA) and in Tahiti, cultured L. stylirostris and L. vannamei. It produced a world record of 20- 25 ton ha^-1year^-1 with two crops, in a similar limited water exchange system leading to a better understanding of the benefits of BFT to shrimps in terms of increasing yield (Aquacop 1993).

On the contrary, Avnimelech (2009) asserted that, the pioneering work of BFT could be traced back to 1980’s by Steve Serfling and Dominick Mendola in solar aquafarms in California. They developed an active microbial suspension system termed ‘microbialsoup’ for farming of shrimp and fish (Rosenberry 2007). Later, Balfour Hepher and his colleagues in Israel developed the concept of a ‘heterotrophic food web’, which was encouraged by constantly keeping uneaten feed and excreta suspended by paddle
wheels installed in the ponds/tanks (Hepher 1985). The high dissolved oxygen as well continuous mixing were suggested to aid in the ability of heterotrophic bacteria to partly convert the suspended organic material into microbial biomass, which
flocculated and became available as additional nutrients to the fish (Hepher 1985).

During the mid-1990’s, BFT rapidly developed into a scientific and practical concept when Steve Hopkins and his team in South Carolina, USA, as well as Yoram Avnimelech and his team in Israel independently and concurrently developed what is today known
as BFT (Avnimelech 2009). This system was developed to be a minimal to zero water exchange system and the addition of a carbon substrate that is low in nitrogen (wheat flour or sorghum flour), were added to prevent the accumulation of nitrogen
(Avnimelech et al. 1994). The idea of adding carbon substrate came from the work of Diab and Avnimelech (unpublished), where it was observed that bacteria feeding on carbonaceous substrate that are poor in nitrogen did take up nitrogen from water to produce cell proteins (Avnimelech et al. 1994).

The crux of the technology———-

Despite the development of BFT and operating with relatively simple principles, this did not become an accepted fish culture system by farmers until the 2000’s. Avnimelech (2009) noted that one reason for this hesitation was that the high turbidity, caused by the bioflocs, appeared to go against the principle that the clearer
pond water the better. The eventual acceptance of BFT was mainly due to reasons including; increased scarcity of freshwater, enacting stricter regulations on the amount of wastewater discharge by some developed countries (Boyd 2003) and severe outbreaks of viral shrimp diseases, which was fast spreading among the neighbouring
farms that have connecting water use.

Various names of Biofloc Technology coined by different researchers———-

Over the years, BFT has been called various names by different researchers as follows

active sludge or suspended bacteria-based system (Rakocy et al. 2004)
microbial floc system (Avnimelech 2007; Ballester et al. 2010)
single-cell protein production system (Avnimelechet al. 1989)
suspended-growth systems (Hargreaves 2006)
zero exchange autotrophic-heterotrophic system (ZEAH; Burford et al. 2003, 2004; Wasielesky et al. 2006)
Aerobic Microbial Floc System (Felix,2015)

Preferrable Species for the practice of Biofloc culture Technique

Avnimelech, 2012 — • BFT can promote the growth of fish that are better filter feeders

Emerenciano et al. (2013)—

Categorically stated that not all species of fish are
candidates of BFT, and are limited to only species that have effective filtering apparatus (such as shrimps and tilapia).

Also fishes with omnivorous feeding habits that can
feed on small particles.

Felix (2015) — • Species being able to tolerate intermediate DO levels (as low as 3 mg L^-1)

High amounts of suspended solids and elevated
stocking densities.

To produce 1 kg live weight fish one needs 1-3 kg dry weight feed (assuming a food conversion ratio about 1-3) (Naylor et al., 2000). About 36% of the feed is excreted as a form of organic waste (Brune et al., 2003). Around 75% of the feed N and P are unutilized and remain as waste in the water (Piedrahita, 2003; Gutierrez-Wing and
Malone, 2006). An intensive aquaculture system, which contains 3-ton tilapia, can be compared on a biomass basis to a human community with 50 inhabitants (Helfman et al., 1997). This intensive aquaculture system can also be compared in terms of waste generation to a community of around 240 inhabitants (Aziz and Tebbutt, 1980; Flemish government, 2005). It can thus be concluded that live fish biomass generates approximately 5 times.

Nitrogen utilization enhancement of culture systems that have been developed to re-utilize nutrient waste on the basis of nutrient recycling and on integrated culture systems with species that directly or indirectly utilize the waste

Species	N input (kg/ha)	% N harvested	N utilization enhancement (%) relative to monoculture	P input (Kg/ha)	%P harvested	P utilization enhancement (%) relative to monoculture	Reference
White shrimp,biofloc	352	39	31-70	45	35	66	Da Silva et al.,2013
Nile tilapia,periphyton	156	37	45	211	83	36	Hendriana et al.,2016
White shrimp,red tilapia	236	41	50	59	19	109	Yuan et al.,2010
Chinese shrimp,red tilapia constricted tagelus	–	21	75	–	14	100	Tian et al.,2001

The Biofloc systems are versatile, friendly and forgiving systems. They are versatile since you have a choice of how to develop your system. You can choose what degree of intensity suits your needs, what shape and size of pond you choose, what percentage of water exchange you want (or can afford), do you want to have higher
or lower dominance of heterotrophic bacteria, etc.,There is no necessity to introduce the inoculum for the biofloc development. If you desired to have a rapid development of the biofloc system, you need to start early feeding of the pond system, and in some
cases inoculation is favourable.This is especially important if you fill the pond with outside water of suspected quality, and sterilize the water, usually with different chlorine compounds.The choice of inoculum and the need to add inoculum open a large variety of possibilities. Firstly, adding inoculum is not a must since most systems contain a large variety of microorganisms serving as a natural inoculum.

Customization of Biofloc Systems

These days, commercially various models of circular tanks made with LLDPE (Linear Low Density Polyethylene) ,PVC (Poly vinyl chloride) liners are available at different with Round tanks and small round ponds have proven effective for culturing shrimp
in super intensive biofloc systems. Circular water movement can be achieved with relatively low energy input and water homogeneity is facilitated. Round ponds with circular flow can have a drain at the center to remove settled solids, facilitating efficient solids management. However, it is difficult to utilize farm space effectively
with round systems.

Many super intensive shrimp biofloc systems are contained in raceways long narrow tanks. Raceways are typically rectangular in shape, but with rounded corners. A central wall or baffle spans the majority of the longer dimension. Water can be propelled around this wall to encourage thorough mixing of the system. Raceways are usually sloped towards one end to facilitate proper draining during harvest, and they utilize space more effectively when contained within buildings.

2.Fertilization Prototype for Biofloc Development & Maintenance Development of Biofloc

The use of different carbon sources has a variable role in the growth of the heterotrophic microbiota with a distinctive effect on water quality and utilization of the flocs by the cultured organisms. The organic carbon can be supplied either as an additional organic carbon source or by changing the feed composition thus increasing
its carbon content. It is possible theoretically to calculate the amount of organic matter needed for an intensive pond, based on the amount of nitrogen excreted by the aquaculture species.

The list of fertilizers used for the biofloc development is listed in the below table

Day	Fertilizers	Quantity (g/ton)
1	Urea	1.1
	Triple super phosphate (TSP)	0.14
	Grain pellet	4
	Dolomite	7
2	Grain pellet	4
	Dolomite	7
3	Grain pellet	4
	Dolomite	7
4	Grain pellet	4
	Carbon source	10.1
5	Grain pellet	4
6	Carbon source	7

Management of Carbon :Nitrogen (C:N) ratio

The management of C:N ratio in Biofloc culture ponds is normally divided in two phases:

(i) Initial and formation phase- Carbon :Nitrogen ratio- 12-20:1

(ii) Maintenance phase- Carbon-to-nitrogen ratio of 6:1 (if TAN values >1mg/L).

In the beginning of culture period, high carbon-to-nitrogen ratio (12-20:1) in water is a key factor to promote and stabilize the heterotrophic community in BFT. High carbon concentration will induce the nitrogenous by-product assimilation by heterotrophic
bacteria and also will supersede the carbon assimilatory capacity of algae, contributing to bacteria growth.

Calculation of the amount of carbon to be added

20kg of carbohydrate is required to reduce 1kg of ammonia (Avnimelech 1999). The total amount of carbohydrate supplementation required to remove the ammonia-nitrogen generated from a given amount of feed can be calculated using the following relationship:

kg CHO = kg feed x kg N/kg feed x kg NH4-N/kg N x 20 kg CHO/kg NH4-N The amount of carbon to be added can also be represented using a typical example The stocking density of the culture animal (50 kg/m³)

Feeding intake (2% of body weight)

Feed dosed in the pond for 50kg/m³ at the rate of 2% body weight = (50000g x 2%)1000 g of feed/ m³

Amount of protein in fish feed (avg. 30%)

Amount of protein dosed in the pond (for 1000g of feed) = (1000 x 30%) 300g/m³16% of protein is nitrogen so the daily amount of nitrogen fed in the pond = (300 x 16%) 48g of Nitrogen/m³

Amount of nitrogen ending up in the pond (75% of the nitrogen fed) = (48 x 75%) 36g of N/m³

For maintaining the C:N ratio of 10: 1 amount of carbon needed for nitrogen assimilation (added for 36g of N/m³) = 36 x 10= 360g of carbon/m³

Based on the dry matter of the carbon in the carbon source the amount of the carbon to be added varies. In general 50% of the dry matter contains carbon, so the amount of carbon added = (360 x 2) = 720g of carbon/m³

3.Complementary and Competitive Role of Microbes and Planktons in Biofloc Systems

There are complex interactions among the different classes of microorganisms in BFT which are complementary or competitive and a range of stimulatory and inhibitory functions between algae and bacteria in the system (Fuentes et al. 2016).
Three major nitrogen conversion pathways involved in the aquaculture includes Photoautotrophic, chemoautotrophic and heterotrophic systems. Photoautotrophic conversion of ammonia-nitrogen involves the uptake of ammonia-nitrogen (ammonia-

N) by phytoplankton (algae) and is often relied on in traditional pond systems. Chemoautotrophic conversion of ammonia-nitrogen method does not remove nitrogen from the system but rather converts toxic ammonia-N to less toxic nitrate-N in a process called ‘nitrification’ (Timmons et al. 2002).

Heterotrophic conversion of ammonia-nitrogen increase the carbon to nitrogen ratios of the water shifts the microbial community from microalgae and chemotrophic bacteria to heterotrophic bacteria. Increased carbon to nitrogen ratio enhances the metabolic activities of heterotrophic bacteria, hence, lead to dominating such environment. These bacteria convert nitrogenous metabolites into potentially consumable biomass, which is the basis behind BFT (Crab et al. 2012).

Characteristics of Major Nitrogen Pathways in Aquaculture

Photoautotrophic

Chemoautotrophic

Heterotrophic

Ammonia-nitrogen is

removed through uptake

by phytoplankton

Ammonia-nitrogen is

converted to less toxic

nitrate

Ammonia-nitrogen is

converted to consumable