Particle size reduction by breakage in biological wastewater treatment

Abstract

Floc breakup in biological wastewater treatment occurs in response to hydrodynamic stresses imposed by aeration, recirculation, and mixing. This size reduction is of particular concern because it leads to solids carry-over and adversely affects process controllability. A laboratory study of floc size reduction has shown how the hydrodynamic environment causes breakup and the extent to which it proceeds at particular levels of dissipation. The structure of jet flows was found to be well-suited for the reduction of floc size.

Physical Characteristics of Activated Sludge Flocs

“…The densities of solutions where the floes do not settle are considered those of the floes. The idea was suggested and adopted in the experiments by Schoepfer and Zemke (cited by Mueller et al 33 ), Mueller et al, 35 Lagvankar and Gemmell, 103 and Ozturgut and Lavelle. 106 Mueller et al 35 measured the density of the activated sludge as a whole instead of each individual floe, as did the others.…”

“…The balance of the two forces gave the maximum floe diameter to be a function of energy dissipation rate per unit mass. This kind of function was also developed or adopted by Tomi and Bagster, 121 Tambo and Hozumi," 6 and Glasgow et al 33 Since the energy dissipation rate per unit mass can be well correlated to the fluid velocity gradient G, which is a popular parameter used in activated sludge studies, under given conditions, more investigators described the floe maximum stable diameter generally as different exponential functions of the velocity gradient G. 13121122 Floe strength cannot be observed directly. To reveal its degree, various methods have been studied and used by many investigators.…”

“…The same equipment, but computerized, was used by Roth and Pinnow 20 for counting and sizing activated sludge floes. Glasgow et al 33 reported that their negatives, taken from activated sludge floes, were analyzed with a Bausch and Lomb® Omnicon image analysis system. These two instruments work in a similar way, i.e., an optical video signal created by the blocking of the light path by the floes is converted to a two-level electrical binary signal which is then processed in the preselected measurement module.…”

The Simulation of Dispersed-Phase Breakage Phenomena

“…The principal references in this area include Thomas (1964), Parker et al (1972), Glasgow and Luecke (1980), and Glasgow et al (1983). Additionally, one cannot move very far into the theory of floc breakage without discovering the need for a description of floc strength;…”

Untitled

“…The value of y indicates the breakup mechanism which dominates. In many cases floc erosion and floc fragmentation occur simultaneously (Glasgow and Luecke 1980). Other complex expressions have been developed for calculating C as well (Parker et al 1972;Tambo and Hozumi 1979).…”