The effect of acid cleaning on a fine pore ceramic diffuser aeration system

Fine pore ceramic diffuser aeration, a very competitive high efficiency system, is widely used in aerobic biological processes for providing dissolved oxygen and mixing. Concern has been registered regarding the maintenance of these systems and their susceptibility to diffuser fouling. Selected ceramic diffusers, removed from the Madison Metropolitan Sewage District (MMSD) Nine Springs Wastewater Treatment Plant, Wisconsin, U.S.A., were fractured and analyzed in an attempt to identify the elemental components of the internal foulants and to evaluate the effect of acid cleaning on diffuser performance. The fouling condition of diffusers were initially characterized by dynamic wet pressure (DWP) measurements. Microimages taken from the non acid-treated diffuser profile using scanning electronic microscopy revealed the structural difference of internal foulants which may correspond to the stage of foulant formation. For diffuser samples from the MMSD facility, calcium phosphate minerals were predominant foulants, although some calcium carbonate and organic carbon have also accumulated. The clogging of diffuser internal void space was verified by observing thin sections of diffuser cross-sections. Selected diffusers were then treated with strong acid to study its effectiveness in removing internal foulant by acid soaking. Even though the acid treated diffusers showed significant reduced DWP values, acid treatment, the common diffuser cleaning technique, does not completely remove these internal foulants. This may be the reason why the acid-treated diffusers never reached like-new conditions. Furthermore, once these acid-treated diffusers are installed back to the aeration tank, these dewatered foulant sections may very well behave as seed for future clogging.