Evaluation of air-lift pump capabilities for water delivery, aeration, and degasification for application to recirculating aquaculture systems

A methodology is demonstrated for evaluating the feasibility of using air-lift pumps for water movement, aeration, and degasification in a recirculating aquaculture system. A set of empirical equations are presented modeling the performance of a 5.08-cm (2″) diameter air-lift submerged 91.44 cm (36″) with a 15.24-cm (6″) lift operated at 28–142 l min −1 (1–5 scfm) of air injection. A steady state mass balance on oxygen and carbon dioxide, equating the system requirements to the air-lift capabilities is illustrated. Using the empirical relationships developed and standard methods to estimate system O 2 demand and CO 2 production, equations are derived to calculate steady state DO and DC concentrations for any number of air-lifts used in a given recirculating system. The predicted air-lift performance in a typical system indicates the water delivery capacity for low head applications is significantly above the gas exchange capabilities. It is recommended that air-lifts be designed for water delivery and that the demonstrated methodology be used to estimate their supplemental aeration and degasification performance. Open-water aeration is shown to be more energy efficient than aeration using air-lifts. The data suggests that, for blown air systems, when the aeration requirements are met, the carbon dioxide stripping requirements are also. Suggestions for designing recirculating systems utilizing air-lifts are also presented.