Abstract Aeration experiments were conducted in a brick masonry tank of dimension 5.25m×2.87m×1.57m to study the effects of positional angle of propeller shaft (α), submergence depth and rotational speed of shaft on standard aeration efficiency (SAE) of a propeller-aspirator-pump aerator. Non-dimensional numbers related to standard aeration efficiency (SAE) and wire power (P) termed as E and Ne, respectively, were proposed. To evaluate the optimum geometric condition, i.e., positional angle of propeller shaft (α), aeration experiments were conducted at different values of α: 30°, 45°, 60°, 75° and 90°, keeping the rotational speed N (2130rpm) and submergence depth of propeller shaft d (300mm) as constants. The results showed that SAE becomes maximum at α=75°. In a similar way, keeping the geometric condition constant (α=75°), aeration experiments were further conducted at different rotational speeds of propeller shaft, N (1420, 1775, 2130, 2485 and 2840rpm) and different values of submergence depth, d (140, 220, 300, 380 and 460mm) to evaluate the effect of dynamic conditions on aeration characteristics. It was found that E as well as Ne could be well correlated with Froude number (Fr) and Reynolds number (Re), respectively. Finally, maximum SAE of 0.42kgO2/kWh was obtained at positional angle of 75°, rotational speed of 2840rpm and submergence depth of 0.14m of propeller shaft.