Environmental Engineering FOURTH EDITION

Sludge Treatment and Disposal 225

L - Bowl length

B - Beach length

D - Bowl diameter

2- Pool depth

S - Scroll pitch

a - Beach angle

oB - Bowl speed

os - Scroll speed

Figure 10-15. Solid bowl centrifuges. (Photo courtesy of Ingersoll Rand and

I. Kriiger.)

A centrifuge must be able to settle the solids first and then move them out of the
bowl. Accordingly, two parameters have been suggested for scale-up between two
geometrically similar machines. Settling characteristics are measured by the sigma
equation (Ambler 1952). Without going into the derivation of this parameter, it is
simply assumed that if two machines (1 and 2) are to have equal effects on the settling
within the bowl, the following relationship must be true:

Qi Q2

E1 E2

- -. (10.7)

The symbol Q represents the liquid flow rate into the machine, and E is a parameter
composed of machine (not sludge!) characteristics. For solid bowl centrifuges, C is