Residuals Management - Public Water Systems - page 778

Fig. 23-14. Solid bowl centrifuges at Verde Water Treatment Plant (Courtesy of City of Phoenix
and Alfa Laval Inc., Warminster, PA)
A 1969 summary of lime sludge dewatering operational data from four softening
plants using centrifugation showed that the cake solids concentrations were in the range
of 55 to 65 percent suspended solids by weight, with a centrate suspended solids
concentration of 500 to 10,000 mg / L. 54 These values are comparable to the summary
of typical operational data from the centrifugation of lime softening sludges presented
in Table 23-19. 55 Another study showed a consistent cake solids concentration of 50
to 60 percent suspended solids with a total suspended solids recovery greater than 90
percent. 27
The apparent relationship between cake solids concentrations and centrate quality
and how each was affected by centrifuge operation can be explained by a plot of
TABLE 23-19. Solid-Bowl Centrifuge Line Softening Sludge
Performance Data
Parameter Typical Range
Feed, percent solids 10-25
Cake solids concentration, percent solids 55-70
Centrate, percent solids 1.0-1.5
Solids recovery, percent 91-96
Centrifugal force, gravities 3,500-4,000
Scroll differential speed, rpm 20-28
Source: Reference 55. (From Water and Waste Engineering, ''Sludge Han-
dling,'' May 1975.)