Fine pore membrane diffusers arc used extensively worldwide for aeration of activated sludge basins. Aeration can account for as much as 60% of a plant's energy usage (Rosso, et al. 2005). Pore fouling and membrane material degradation can reduce energy efficiency of fine pore membrane diffusers to 50% of the original efficiency after just a few years of operation. Tins work investigated oxygen transfer efficiency of polyurethane membrane AEROSTRIr diffusers that have been in continuous use with the original membranes at the Bremerton, Washington municipal wastewater treatment plant since 2001. Results of clean water testing and off-gas testing in 2012 and 2013 indicated that the eleven to twelve year-old diffusers were operating at ~80% of their original efficiency. A simple pressure washing technique increased oxygen transfer rate of the eleven to twelve-year old diffusers to ~90% of the original efficiency, resulted in a measured SOTE of 7.4%/m (2.3%/ft) immersion depth, and was effective in reducing header pressure by about 60 mbar (0.9 psi).
Keywords: aeration, diffusers, oxygen transfer, energy, off gas testing