High-performance biocarriers for aquacultures

High-performance biocarriers for aquacultures

The term AQUACULTURES refers to fish farming under controlled conditions.


The aquaculture WR Dabie, Bytow, Poland

Recirculation Aquaculture Systems - RAS
represent a new method of fish farming in which the fish are raised in tanks housed within a building under controlled conditions, instead of in open ponds. This facilitates maximum production throughout the entire year under controlled conditions, and reduces the demand on resources such as water and land.

Fish raised in aquacultures require a continual supply of clean water, at the optimum temperature and required concentrations of oxygen. Recirculation systems filter and purify the water which is subsequently returned to the tanks for fish cultivation.

Waste-water treatment and recycling
are required, in order to purify the effluent and remove dangerous substances and unused fish feed, particularly ammonia nitrogen, which even at concentrations of 1-2 mg/l is highly toxic for fish!!

The waste-water treatment involves both mechanical and biological treatment processes. Feed remains are removed by lamella clarifiers and rotating drum screens, followed downstream by biofiltration in biofilm reactors in which biological breakdown of organic contaminants and ammoniac nitrogen through nitrification and denitrification takes place.


 

The term nitrification refers to the biological oxidisation of the ammoniac nitrogen via nitrite into nitrate, by means of the nitrifying bacteria nitrosomonas and nitrobacter.

Nitrosomonas
NH4+  +  1.5 O2                ®           NO2-  +  2 H+ + H2O       (pH-value sinks)
Ammonium                                Nitrite
Nitrobacter        
NO2-   +   0.5 O2               ®           NO3-     Nitrate

In a further step, the denitrification, the nitrate is reduced microbially into molecular nitrogen in the absence of oxygen:

2 NO3-   +   [ H ]       ®     N2 + 2 OH- + H2O   

Nitrifying bacteria are highly sensitive to organic or anorganic inhibitors, display only a low tendency to flocculation and sedimentation, and grow very slowly.
For these reasons, an efficient retention of active bacteria is essential for the establishment and maintenance of a stable nitrification. Both can be achieved through their immobilisation, ie. their fixing on the surfaces of biocarriers with the formation of biologically highly active colonies, or so-called biofilms. Decisive in ensuring a rapid colonisation and formation of active biofilms are the structure and surface properties of the biocarrier.
LEVAPOR Biocarriers
are adsorbent, porous and highly effective. During their development the focus lay on the issue of their adsorption capacity, as well as their surface properties, which promote a rapid microbacterial colonisation and formation of a biofilm.

 

 

Why use specifically LEVAPOR biocarriers for aquacultures?
LEVAPOR biocarriers are made of porous polyurethane foam impregnated with food-grade activated carbon. This modification of the substance's surface promotes the
◾ Extremely rapid microbial colonisation of the enormous surface and the formation of highly active biofilms,
◾ Adsorption and subsequent biological breakdown of inhibiting contaminants, which allows the biological regeneration of the adsorbing surfaces,
◾ Substantially higher efficiency and more stable bioprocesses through buffering, facilitating
◾ Substantially lower formation of sludge.

 
The Biofilter Pilot Plant with LEVAPOR Biocarriers

 

Immobilised micro-organisms are far more resistant to inhibitors, and fluctuations in the pH and temperatures, and consequently survive appreciably longer without nutrition and water than in suspended form. Our trials have shown that dried immobilised bacteria can be fully reactivated after being stored for 12 months.

Advantages of deploying LEVAPOR in bioprocesses:
◾ Short start phase
◾ Higher bio-activity of biofilms
◾ Higher reactor performance and process stability
◾ Lower reactor filling (only 12-15 vol.%, compared to 40 to 70 vol.% )
◾ Lower operating costs
◾ Substantial economic benefits
◾ Mechanical protection of the biofilm established inside the carrier, and
◾ Improved use of O2 through the longer presence of air bubbles within the pores.


 

The impact of various carrier materials on the biological elimination of NH4N and NO2N in aquacultures