A Comparison of Fine Bubble Diffused Aeration and Mixer/ Aerators at the Portland Water District’s East End WWTF

The existing mechanical surface aerators at Portland Water District’s 79 million liter per day (20.8 mgd) East End Wastewater Treatment Facility are nearing the end of their useful service life and cannot maintain adequate dissolved oxygen. The PWD commissioned an evaluation of potential aeration improvements to replace the existing aeration equipment while improving settleability and process reliability. Two aeration technologies were evaluated to replace the existing surface aeration system; fine bubble diffused aeration and INVENT® mixer/aerators. Fine bubble diffusers were recommended for replacing the existing surface aerators since the mixer/aerator system has substantially greater capital and energy costs. The net present worth costs of diffused aeration versus mixer/aerator systems or other aeration technologies can be highly site specific. Numerous factors including WRRF capacity, basin layout, existing electrical facilities and capacity, electrical costs, wastewater strength and daily/diurnal patterns, and treatment objectives all need to be accounted for when comparing aeration equipment.