World Aquaculture Society Meetings

Sustainable Recirculating Aquaculture Systems (SRAS) utilizing a Vacuum AirLift (VAL) for foam Fractionation, Carbon dioxide stripping, Oxygen replenishment and water circulation

Emmanuel Briquet*, Bertrand Barrut, Jean-Paul Blancheton, Myriam Callier, Jean-Yves Champagne, Alain Grasmick
Searen, LLC
3846 Marburg Avenue
Cincinnati, OH 45209

In Sustainable Recirculating Aquaculture Systems (SRAS) there is a continual accumulation of micro particles from unconsumed food, feces, parasites and bacteria.  In addition there is a continuous depletion of oxygen and a buildup of carbon dioxide in the water.  These factors reduce the water quality causing stress that leads to slower growth and reduced yields. The fouling of the water is compounded by the high density of reared organisms (fish or shellfish) in a SRAS environment.  Without corrective action to remove these contaminants, they will accumulate to the point that they create a toxic environment for the organisms.  This study summarizes research directed toward the advancement of a new technology that will enhance aquaculture production through improved animal health, improved aquaculture production yield, reduced water usage, reduced capital costs and increased energy efficiency.  These improvements are accomplished through the application of Vacuum Air Lift (VAL) technology to SRAS.

The accumulation of particulate organic matter (POM) in SRAS has become an important issue with the intensification of finfish production. The objective of this study was to assess the foam fractionation efficiency of a VAL in different conditions (POM concentrations, airflow rates, bubble sizes, water renewal rates and feed addition). In sea water, the vacuum airlift allowed removing 20% of the initial POM concentration per hour (foam fractionation efficiency), corresponding to a 20.7-fold concentration factor between the tank and the foam. Calculated POM production by fish ranged between 15.9 and 23.5 g h−1 and was equivalent to estimations based on feed conversion ratio (FCR). This indicated that the entire POM produced was extracted by the vacuum airlift.

In aquaculture, oxygen transfer and carbon dioxide stripping are the first limiting factors to fish rearing intensification. This study measured the O2 and CO2 mass transfer coefficient (KLa) for a vacuum airlift in fresh (<1‰ salinity) and sea water (35‰ salinity) SRAS. Several types of air injectors were tested, delivering different sizes of bubble swarms depending on their porosity and functioning conditions (low or high injection pressure), with air flows varying from 0 to 80 L min−1. For SRAS, the vacuum airlift provides a Standard Aeration Efficiency (SAE) of 1.13 kgO2 kW h−1 and a Standard Stripping Efficiency (SSE) of 1.8 kgO2 kW h−1 or 0.023 kgCO2 kW h−1.

A study was undertaken to measure the water flow (Qw) delivered by a VAL designed for SRAS in fresh (<1‰ of salinity) and sea water (35‰ of salinity). The VAL consists of two concentric tubes connected at their top to a chamber at partial vacuum. When working with low head SRAS (under 0.3 m), the VAL could save up to 50% of the energy required for centrifugal pumps.

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