Standard Aeration Efficiency Research Articles

Design and peroormance of paddle wheel aerators

An apparatus was constructed for testing the influence of paddle shape and depth and paddle wheel speed and diameter on oxygen-transfer characteristics of paddle wheel aerators. Paddles triangular in crosssection were more efficient than other paddle shapes. Standard oxygen transfer rate (SOTR) increased with increasing paddle depth and paddle wheel speed while standard aeration efficiency (SAE) declined. For a particular depth and speed, SOTR increased with increasing paddle wheel diameter. The greatest SAE (2·96 kg O 2 kWh −1) was achieved with a 91 cm diameter paddle wheel with triangular paddles operated at 77 rev min −1 and 12·5 cm paddle depth. Three companies made floating, 7·5 kW electric paddle wheel aerators according to design specifications developed in this research. These commercial aerators had high values for SOTR (18·8–21·8 kg O 2 h −1) and SAE (2·7–2·9 kg O 2 kWh −1) and were much more efficient than other aerators used in channel catfish farming.

Performance of Surface Rotors in an Oxidation Ditch

Oxygen transfer tests were conducted on surface rotor aerators installed in a plant scale oxidation ditch. The effects of rotor rotational speed on the standard oxygen transfer rate, the net power input, and the standard aeration efficiency are presented. Initial nonuniform distribution of deoxygenating chemical in a circulating tank can result in poorly behaved data. The circulation pattern in an oxidation ditch is accurately modeled by the first order oxygen transfer rate equations applied to a completely mixed batch reactor. Oxygen transfer rates estimated by the nonlinear regression and best fit log deficit methods of data analysis vary less than ±10%, and the results of the two analytical methods are identical for practical purposes. A rotor cover which restricts the spray pattern of the rotor can result in increased oxygen transfer rates at the expense of an increase in power and a decrease in ditch flow velocity.