THE PERFORMANCE OF NEW AIRLIFT AERATORS AT DIFFERENT SALINITIES, USING DIFFERENT BLOWER POWERS

In semi-intensive and intensive aquaculture, aerators are necessary to satisfy the oxygen requirements for respiration of the cultured organisms. There are many kinds of mechanical aerators. One bubbler aerator is the diffused-air aeration system, which releases air bubbles near pond or tank bottoms to rise through water column. This study was conducted to determine the influence of different salinities and different blowers on the performance of two new airlift aerators.

The tests were performed in indoor tanks located at the Auburn University E. W. Shell Fisheries Center, Auburn, AL. The approximate tank volumes were 3.5 and 7 m³, but actual water volume was estimated during each test. The tanks were supplied with clean city water. The procedure for conducting the tests followed protocol suggested by the American Society of Civil Engineers. The procedure involved deoxygenating water in the tank with sodium sulfite and cobalt chloride, measuring dissolved oxygen concentration during reaeration by using smarTROLL RDO handheld oxygen meter (In-Situ Inc.), and calculation of the oxygen transfer coefficient (K_LaT). The value for the K_LaT was adjusted to 20°C. The adjusted value (K_La20) was then used to calculate the standard oxygen transfer rate (SOTR). The wire power was computed and divided into SOTR to provide the standard aeration efficiency (SAE) in kilograms of oxygen per kilowatt hour. The SOTR and SAE of two airlift devices - Hydro Burst^® and Hydro Stream^®- (Aqua Hill Aeration Inc.) were tested at five salinities (0.1, 10, 20, 30 and 40‰). Three different blower power (0.37, 0.75 and 1.5 kW) were tested at all salinities. Three replicate trials were performed with each airlift device with each blower at each salinity.

The results clearly demonstrated a significant effect of salinity on airlift aerators oxygen transfer performance. This is because air bubbles are more numerous and smaller in saline water than in freshwater. Our findings also showed that, the bigger the blower, the higher the SOTR, the smaller the SAE. There is a trade-off between SAE and SOTR. The SAE is an important but not the critical factor for tanks.