Sludges occur in water treatment systems as a result of turbidity removal, softening, and filter backwash. The dry weight of sludge produced per day from softening and turbidity removal operations can be calculated using Equation 9.1 (Lang et al., 1985):
S = 84.4Q(2Ca + 2.6Mg + 0.44Al + 1.9Fe + SS + Ax) (9.1)
Q = Design water treatment flow (m3/s).
Ca = Calcium hardness removed (as CaCO3; mg/L).
Mg = Magnesium hardness removed (as CaCO3; mg/L).
SS = Raw-water suspended solids (mg/L).
Ax = Additional chemicals (e.g., polymers, clay, activated carbon) (mg/L).
The major components of most of these sludges are due to the suspended solids (SS) from the raw water and the coagulant and coagulant aids used in treatment.
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