Mixed Aeration: Using Pure Oxygen to Supplement Oxygen Requirements in High Rate Processes

Pure oxygen supplementation of air-based systems has been used successfully as a low cost, easy to implement solution to short and long term oxygen requirements. When implementing such devices, one typically assumes the volumetric mass transfer coefficient, kLa, for pure oxygen is the same as for air. This may be justified, since oxygen diffusivity is slightly higher than air (11%) but the interfacial area for pure oxygen transfer is lower (-18% at 30% oxygen utilization). Large scale clean water tests were conducted with air and pure oxygen for fine bubble membrane diffusers at 7-49% basin coverage, flows between 0.5 and 6.1 Nm3/h/mdiff and depths of 3 and 6 meters to compare the kLa values. In all cases the kLa for oxygen was higher, attributed to the increase in diffusivity and reduced coalescence of smaller bubbles.