Influent Treatment
Culture Systems
Effluent Management
Fish Handling
Information Request

Partial Reuse Aquaculture Systems (PRAS)

Partial Reuse Aquaculture Systems (PRAS) use water treatment processes to allow a portion of the culture discharge water to be recycled and supplied back into the culture tanks. For aquaculture facilities faced with limited water resources, sustainability issues, or a requirement for improved control over culture conditions, reuse technology is the next step in the technological evolution of modern aquaculture systems.

When compared to flow-through aquaculture systems, PRAS offer significant reductions in water consumption, effluent discharge volumes, and potentially energy consumption. Reuse technology allows for location of new facilities where there are limited water resources, and allows existing facilities to increase production despite limited water resources. With reduced water use, influent treatment and effluent treatment become more economical. As such, disinfection of influent water for biosecurity protection becomes possible and impact of the facility on the environment may be better mitigated. In addition to these benefits, water quality and temperature become easier to control which may have production benefits.

Partial Reuse Systems focus on the use of a few, simple treatment technologies to provide significant reductions in water use. These technologies typically include gas balancing and oxygenation, may also include solids removal and disinfection, but do not normally include ammonia removal through biofiltration. Those water quality parameters for which treatment is not provided are maintained within acceptable limits by flushing and replacement of a portion of the system water. Water temperature is dependant on influent water temperature which may be more economically altered than in flow-through system due to the reduced flow.

Because flushing and water replacement is used to control the concentrations of some contaminants, the reuse rate is limited by the accumulation of untreated contaminants such as ammonia. The maximum reuse rate that may be achievable without the addition of more advanced treatment processes will depend on the biomass and feed load on the system, and on the specific water quality requirements of the fish cultured. Partial reuse rates from 50% to 90% of the total flow have been employed, depending primarily on fish sensitivity to unionized ammonia concentrations, although reuse rates between 50% and 75% are most common. 

More Info >>>

As reuse rates increase, the reduced exchange of system water may allow untreated contaminants such as ammonia and suspended solids to concentrate in the system.  Recirculation Aquaculture Systems incorporate additional treatment processes to reduce the concentration of these contaminants, allowing for further water conservation through increased reuse rates.

Recirculation >>>

Partial Reuse Facts

  • Significantly reduced water consumption and effluent volumes (50%-75% typical)
  • Allows for significant production expansion without increasing water use
  • Reductions in energy consumption are possible when influent pumping costs are high
  • Typically lower capital investment compared to recirculation systems but higher than flow-through systems
  • Site placement is less dependant on water availability
  • More economical influent treatment and temperature control
  • Disinfection of influent water for biosecurity protection is more economically
  • Much less mechanical and operational complexity than recirculation systems but higher than flow-through systems
  • Control of culture conditions is improved
  • Reduced volumes result in more economical effluent treatment
  • Therapeutic treatments are efficient and economical