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Gas Transfer in Air-lifts Used to Recirculate Aquaculture Systems

by Hearn, Ryan Anthony

Abstract (Summary)
The following studies were conducted to determine hydraulic, aeration, and degasification characteristics associated with various air-lift pumps. The first study presented data on a 20.3 cm air-lift used to support adult Yellowtail broodstock (Seriola lalandi) in an oligotrophic warmwater marine RAS (recirculating aquaculture system). Empirical relationships were used to estimate actual oxygen and carbon dioxide mass transfer rates (AOTR & ACTR) as the inlet oxygen or carbon dioxide concentrations were perturbed under lift heights of 30.5, 38.1, and 45.7 cm. Transfer rates, kg of constituent per day, were found to be dependent on air injection depth and volume, aqueous gas concentrations, and lift height. Liquid flows ranged from 623 1,117 l min-1 for corresponding air injections of 850 1,415 l min-1. Certain extremities show the tested air-lift capable of providing 3.13 kg O2 day-1 while concurrently stripping 28.32 kg CO2 day-1. The second study examined standard oxygen and carbon dioxide transfer rates (SOTR & SCTR) for 10.2, 15.2, and 20.3 cm SUTA (siphoning u-tube air-lift) pumps in low-head, freshwater recirculation systems. Results varied as pipe diameter, gas to liquid ratios, and lift to submergence ratios varied; with transfer rates increasing with pipe diameter and air injection volume. SOTR values ranged from 0.0594 kg O2 hr-1 to 0.2073 kg O2 hr-1 while SCTR varied between 0.0013 to 0.0061 kg CO2 hr-1. All configurations were capable of stripping CO2 less than 20 mg l-1 while targeting DO levels of 5 mg l-1. Steady state analysis shows that 20.3 cm air-lifts can meet O2 consumption and CO2 production rates of broodstock, fingerling, and growout categories in warmwater marine environments. As feed rate varied from 4 to 17 kg feed day-1, oxygen and carbon dioxide levels were sufficiently maintained for broodstock and fingerlings, with supplemental air recommended for growout conditions.
Bibliographical Information:

Advisor:Willson, Clinton; Theegala, Chandra; Malone, Ronald

School:Louisiana State University in Shreveport

School Location:USA - Louisiana

Source Type:Master's Thesis

Keywords:civil environmental engineering

ISBN:

Date of Publication:07/09/2009

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