A Feasibility Study of Using Air-lift Pumps for Aeration, Degasification, and Water Movement in a Recirculating Aquaculture System
Date of Award
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.
Loyless, John Clay, "A Feasibility Study of Using Air-lift Pumps for Aeration, Degasification, and Water Movement in a Recirculating Aquaculture System" (1995). LSU Historical Dissertations and Theses. 8311.