Increasing the use of sustainable practices in the aquaculture industry is vital to meeting increasing global demands for seafood products. One suggested approach to reduce environmental impacts on wild ecosystems and improve the sustainability of the aquaculture industry is to remove fish production systems from natural bodies of water and relocate them to land-based facilities. Moving fish production systems to land based-tanks however, increases the demand for freshwater resources and increases energy costs due to the requirement to run pumps, aerators and lighting systems.
To overcome these challenges, this study presents a gaslift pump technology designed to handle heavy fluids or liquid-solid mixtures with high mass transfer capabilities and with minimal energy requirements. This design was created using fundamental knowledge of multiphase flow in which the mixture takes on different patterns when the gas, liquid and solid phases are moving together in the same passage at different velocities. The pump’s gas injector was designed while considering the ratio between the density of the liquid/solid and the gas phases, utilizing the buoyancy forces for optimal pump operation. This pump does not require any mechanical or moving parts or lubrication and uses much less energy to operate with negligible noise and vibration. It offers the end users (fish farmers and food processing facilities) the advantage of a simple design that can be easily integrated in existing piping systems with minimal installation costs. It has lower operating costs (at least 40%), lower capital investments (70 to 80% less) and requires minimal maintenance compared to conventional mechanical pumps. It is easy to use for pumping liquid-solid mixtures or non-Newtonian fluids, such as transferring fish/shrimp in aquaculture farms, moving nutrient solutions/solid mixtures in hydroponics or moving waste in food processing applications. Field tests of these pump were carried out at the Ontario Aquaculture Research Centre - Alma (previously known as the Alma Aquaculture Research Station established by OMAFRA and the University of Guelph to assist the commercial fish farming industry in Ontario).
The objective of these tests were to quantify the effects of the gaslift pump technology on the water quality parameters and fish productivity in a commercial aquaculture setting compared to traditional aeration devices. Five thousand Arctic char (Salvelinus alpinus) sourced from the Ontario Aquaculture Research Centre were distributed amongst two grow-out tanks, one utilizing a standard aeration device and the other utilizing the gaslift pumps. Over a 3-month period, fish growth and performance were monitored and measured along with the dissolved oxygen concentration, total suspended solids, temperature, turbidity and surface velocity in comparison between the two tank systems. Results showed an increase in dissolved oxygen in the tank containing the gaslift pumps as well a reduced number of suspended solids due to the recirculating motion created by the pumps, allowing for better solid filtration within the tank. This recirculation was captured using surface velocity distributions mapped out to fully analyze the effects of the gaslift pump on the fish tank. It can be shown that higher velocity can be attained utilizing the gas lift pump while maintaining consistent air injection flow rates, when comparing it to velocities reached with the standard aeration device. Overall, it is observed that the gas lift pump offers sufficient water circulation and increased aeration, which can ultimately improve the quality of fish farms.