Effect of orifice diameter, depth of air injection, and air flow rate on oxygen transfer in a pilot-scale, full lift, hypolimnetic aerator

Abstract

A pilot-scale, full lift, hypolimnetic aerator was used to examine the effect of diffuser pore diameter, depth of diffuser submergence, and gas flow rate on oxygen transfer, using four standard units of measure for quantifying oxygen transfer: (a) KLa20 (h -1 ), the oxygen transfer coefficient at 20 8C; (b) SOTR (g O2� h -1 ), the standard oxygen transfer rate; (c) SAE (g O2� kWh -1 ), the standard aeration efficiency and (d) SOTE (%), the standard oxygen transfer efficiency. Dif- fuser depth (1.5 and 2.9 m) exerted a significant effect on KLa20, SOTR, SAE, and SOTE, with all units of measure in- creasing in response to increased diffuser depth. Both KLa20 and SOTR responded positively to increased gas flow rates (10, 20, 30, and 40 Lmin -1 ), whereas both SAE and SOTE responded negatively. Orifice diameter (140, 400, and 800 mm) exerted a significant effect on KLa20, SOTR, SAE, and SOTE, with all units of measure increasing with decreas- ing orifice size. These experiments demonstrate how competing design factors interact to determine overall oxygen transfer rates in full lift hypolimnetic aeration systems. The practical application for full lift hypolimnetic aerator design is to max- imize the surface area of the bubbles, use fine (i.e., ~140 mm) pore diameter diffusers, and locate the diffusers at the max- imum practical depth.