Date of Award


Document Type



A feasibility study of using air-lift pumps for water movement, aeration, and degasification in a recirculating aquaculture system was conducted. Fluid delivery tests of various air-lift configurations indicated that water flow is a function of the submergence depth, lift height, and air injection rate. The air-lift units were found to transfer 02 at only 1/5 to 1/2 the rate of comparably operated open-water aeration systems. The standard oxygen transfer rate (SOTR) increased with air injection from 1-7 scftn, however, the energy usage also increased, yielding a reduction in the standard aeration efficiency (SAE) from over 2 to less than 0.5 kg 02 / kw hr. Tests comparing airstones to open-ended tubes as air-lift injectors indicated a similar performance. The carbon dioxide stripping rate increased with air flow while the efficiency decreased. The short-term C02 transfer was also shown to decrease as the system alkalinity increased. A set of empirical equations was developed to predict the water flow and steady state dissolved oxygen and carbon dioxide concentrations for any number of air-lifts used in a typical recirculating system. The air-lift configuration modeled was a 2" diameter pipe submerged 36” with a 6" lift operated at I - 5 scfm of air injection. The recirculating system was assumed to be stocked at a fish density of 0.5 Ib/gal, fed at 3% per day, and maintained at 30 °C. The minimum oxygen concentration was assumed to be 6 mg/1 and the carbon dioxide tolerance was selected as 5 mg/1. The predicted air-lift performance in such a system was compared to the estimated water flow and gas exchange demands and the aeration requirement was found to be the controlling design parameter.