FINE PORE AERATION - FIFTEEN YEARS OF OFF-GAS TRANSFER EFFICIENCY MEASUREMENTS

Fine pore diffusers, often called fine bubble diffusers, have nearly replaced coarse bubble diffusers in municipal wastewater treatment over the past 20 years. The rapid increases in energy costs which began in the 1970's created financial incentives to upgrade to this more expensive and maintenance intensive method of aeration. Fine pore diffusers have the added benefit of reducing VOC stripping and reduced aeration heat loss. This paper summarizes more than 15 years of oxygen transfer efficiency measurements using the off-gas technique. Efficiencies are show for different types of diffusers at various depths and mean cell retention times (MCRT or sludge age). The results show that aeration efficiencies are linearly related to depth of submergence, strongly influenced by MCRT, with low MCRT systems having suppressed transfer rates. The α factor is generally independent of fine bubble diffuser type, within the experimental error of the measurements.