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.

Rapid quantitative method for Salmonella detection in polluted waters.

A procedure has been developed for the enumeration of salmonellae in polluted waters using several modifications of existing techniques. Confirmation of salmonellae is achieved within 48 hr. This procedure includes selective enrichment in m-Tetrathionate Broth (22 +/- 1 hr), plating on Brilliant Green Sulfa Agar (20 +/- 1 hr), and confirmation by flagellar (H) agglutination of the growth in a mannosecontaining medium (6 +/- 1 hr). An incubation temperature of 41.5 C was used throughout this procedure. Dilution to extinction techniques (most probable number) were employed to enumerate salmonellae. Large sample volumes were concentrated through the use of membrane filters. This technique proved to be rapid and reliable for the enumeration of salmonellae in water, waste water, and waste-water sludges.

Activated-sludge nitrification in the presence of linear and branched-chain alkyl benzene sulfonates.

The effects of biodegradable linear alkyl benzene sulfonate and branched-chain alkyl benzene sulfonate detergents on activated-sludge nitrification were investigated by administering a synthetic waste containing up to 23 mg of each detergent per liter to eight bench-scale, batch, activated-sludge units. It was found that both detergents tended to promote complete oxidation of ammonia to nitrate, whereas control units produced approximately equal amounts of nitrite and nitrate. Various hypotheses are offered to explain the phenomenon.

Floc sizing techniques.

In the study of mass transfer of substrate through floc particles, it is essential to have an estimate of floc size. This study presents floc size measurements made on pure culture bacterial floc and shows their applicability to mass transfer studies. A critical review of the biological literature on methods to size biological floc and determine wet floc density is also presented.