This is not a peer-reviewed article. International Symposium on Air Quality and Waste Management for Agriculture. CD-Rom Proceedings of the 16-19 September 2007 Conference (Broomfield, Colorado) Publication date 16, September 2007 ASABE Publication Number 701P0907cd Aerator Performance For Wastewater Lagoon Application R. H. Zhang 1 , H. Sun 1 , W.M. Kamthunzi 2 , C. A. Collar 3 , F. M. Mitloehner 4 1 Biological and Agricultural Engineering Department, University of California, Davis 2 College of Agriculture, University of Malawi 3 Cooperative Extension, University of California, Davis 4 Animal Science Department, University of California, Davis Abstract. Six types of mechanical aerators were evaluated and compared for their capacities of transferring oxygen into water and their energy efficiencies. The standard method of American Society of Civil Engineers for testing aerators in clean water was used to determine the standard oxygen transfer rate (SOTR) and standard oxygenation efficiency (SOE) of each aerator. The aerators tested included four types that are typically used for dairy wastewater lagoons and two types that are being used for municipal wastewater lagoons. The names of the first four types were vortitech, black circulator, pond mill and vbttm and the latter two were aire-o2 aerator and aire-o2 triton. The SOTR was determined to be 0.20, 0.42, 0.15, 0.21, 2.66 and 2.93 kg o2/hr, respectively, and the SOE was 0.49, 0.35, 0.36, 0.10, 0.68 and 0.57 kg o2/kwh, respectively. all tested aerators showed lower SOTR and SOE than the published literature values for typical mechanical aerators. The results of this study pointed out the fact that the aerators currently used for dairy wastewater lagoons need significant improvement in their aeration performance in order to match their counterparts in municipal wastewater lagoons. The aerator testing results are important information for decision making with respect to the proper selection of aerators for performing the aeration of wastewater lagoons and estimating the energy requirement of operating the aerators. Keywords. Aeration, dairy wastewater, oxygen transfer rate, oxygenation efficiency. Introduction In wastewater treatment applications, aeration is used to provide oxygen into wastewater to support the growth of aerobic microorganisms for carrying out biological degradation and oxidation of organic and inorganic compounds in the wastewater. Natural aeration occurs at open wastewater surfaces but the oxygen transfer rate is rather low. Ro and Hunt (2006) recently provided a review of different methods for calculating the oxygen transfer rate for open lagoons. Often mechanical aerators are used to enhance the oxygen transfer rate. Based on their working principles, the mechanical aerators include five major types: compressed air, mechanical surface, mechanical subsurface, combined compressed air and mechanical, and pumped liquid (venture) (Cumby, 1987). The performance of mechanical aerators is evaluated by two parameters: 1) oxygen transfer rate and 2) oxygenation efficiency. The oxygen transfer rate is used to determine the number of aerators needed to meet the oxygen supply requirement for a particular aeration application. The oxygenation efficiency is used to estimate the energy requirement for operating the aerators. In wastewater treatment systems, oxygen transfer rate can be affected by several factors: 1) surface area of water in contact with the air or oxygen; 2) mixing or turbulence; 3) saturation deficit (difference between saturated oxygen concentration and actual dissolved oxygen concentration); 4) influence of solid or other constituents in the water; and 5) temperature (Westerman and Zhang, 1997). All of these factors