Recirculating Aquaculture System commonly known as RAS system are gaining popularity for closed loop fish and sea food production under controlled environment due to its numerous benefits such as:

  • Lower Foot Print
  • Lower Water Usage
  • Higher Rearing Density
  • Better quality of fish and sea food
  • Higher production due to lower mortality

During their different growth phases, fish produces a lot of Ammonia nitrogen which if not removed then affect the fish quality and production quantity.

Conventionally for the Reduction of Ammonia nitrogen from the Recirculating Aquaculture Systems water, different carriers based biofilters or MBBRs are utilized for the biological nitrification of the Ammonia present in the RAS water.

Levapor carriers based biofilters/MBBRs provide the most efficient and economical reduction of total Ammonia present in the water for Recirculating Aquaculture Systems.

The high surface area, adsorption capacity due to activated carbon and fine pore structure of Levapor carriers provide distinct advantages compared to conventional plastic carriers for RAS system such as :

  • Smaller foot print
  • Quick Process Start up
  • Lowest possible Ammonia levels in the treated effluent
  • Higher amount of Simultaneous Nitrification and Denitrification (SNDN) offering lowest TAN load in the recirculating water

Above specific advantages of Levapor carriers application for RAS system results in :

  • Better Quality and Quantity of Fish Production due to lowering Ammonia toxicity which reduces mortality and deformities in the fish stock
  • Economical production
  • Lower environmental foot print due to effective reuse of water

At one of the largest salmon hatchery in Europe, different carriers were compared parallel for their ammonia reduction efficiency for the hatchery’s RAS system. The comparative study indicated that Levapor carriers outperformed other carriers for Ammonia and TAN reduction in the system.

Large voids tend to cause detachment of biofilms due to high shear forces and thus would increase the biofilm formation time during the initial colonization. During the event of toxic shock loads, a larger fraction of the biofilm is exposed to the toxicity which may cause performance deterioration.

Smaller and deeper voids allow for rapid formation of biofilms within the deeper pores due to lower sloughing during start up process. Fine pore structure with deeper voids also protects bacteria against toxic shock loads.  So MBBR media with fine pore structure provide much better protection against shock loads and quicker start up compared to the element having large and exposed voids.  

Finer voids also allow for growth of thinner biofilms which keeps a large fraction of biomass present in the biofilm exposed to the bulk liquid of the reactor for substrate uptake. This provide better diffusion gradients allowing better reduction efficiencies.   

Finer and deeper cavities allow for growth of specific type of microorganisms such as Anammox bacteria and Denitrifying bacteria within the inner pores increasing the process efficiency and reliability over the period of operation. However, too fine pore structure may tend to clog the carrier material with excessive biofilm formation within the inner pore and make it heavier. Further due to poor accessibility of the inner pore for substrate, the inner biofilms become less active and redundant over period of operation.

Thus, a MBBR media material having adequate fine pore structure and inner porosity is very much desirable as it provides numerous benefits such as:

  • Faster and better colonization
  • Protection of bacteria against shock loads at the same time provides adequate accessibility to inner biofilms for better substrate diffusion.
  • Adequate detachment, shearing and erosion of biofilms on continuous basis to prevent excessive growth and clogging.
  • Thinner biofilm growth with better diffusion gradients allowing better substrate uptake and reduction efficiencies.

On the contrary present plastic material based MBBR media element have larger voids which has many disadvantages such as:

  • Poor initial colonization due to shearing of biomass during start up.
  • Minimal protection against toxic shock loads before thick biofilms are formed with EPS to protect them.

Poor diffusion gradient with less accessibility to inner biofilms under thick biofilm formation.

Recirculating Aquaculture Systems
Fig 3: Ammonia Nitrogen removal trends for different Carrie

With the team of our RAS experts, We provide our clients complete turn key solutions for their RAS requirement. We help our clients to develop specific RAS models based on their type of Fish, local environmental conditions and rearing densities taken into consideration for the RAS system.

Author Bio

Amit Christian is a MSc graduate in Environment Science from Middlesex University, London, UK. He has been active in the field of water and wastewater treatment since 1998. He specializes in design, engineering, and management of various biological wastewater treatments such as Activated Sludge Process (ASP), Sequencing Batch Reactor (SBR), Moving Bed Bio Reactor (MBBR), Integrated Fixed Film Activated Sludge (IFAS). He has helped various Industrial and Municipal clients in troubleshooting , optimizing their biological wastewater treatment processes to achieve latest Stringent norms for Ammonia Removal.