Activated Sludge Process - Wastewater Operators - page 295

Sludge volume index (SvI)— A process control calculation used to
evaluate the settling quality of the activated sludge. It requires the
SSV 30 and mixed liquor suspended solids test results to calculate:

SSV × 0mg/g

MLSS (mg/L)

(mL/L) 100

30

Sludge Volume Index(mL/g) =

Solids— Material in the solid state.

dissolved— Solids present in solution; solids that will pass through
a glass fiber filter.

fixed— Also known as the inorganic solids ; the solids that are left
after a sample is ignited at 550°C for 15 min.

floatable— Solids that will float to the surface of still water, sew-
age, or other liquid; usually composed of grease particles, oils,
light plastic material, etc. Also called scum.

nonsettleable— Finely divided suspended solids that will not sink to
the bottom in still water, sewage, or other liquid in a reasonable
period, usually 2 hours; also known as colloidal solids .

Suspended— The solids that will not pass through a glass fiber filter.

Total— The solids in water, sewage, or other liquids; it includes the
suspended solids and dissolved solids.

volatile— The organic solids. Measured as the solids that are lost
on ignition of the dry solids at 550°C.

Waste activated sludge (WaS)— The solids being removed from the
activated sludge process.

8.2 aCTivaTed sludge ProCess eQuiPMenT

The equipment requirements for the activated sludge process are
more complex than other processes discussed. Equipment includes an
aeration tank, aeration, system-settling tank, return sludge, and waste
sludge. These are discussed in the following.

8.2.1 aeration Tank

The aeration tank is designed to provide the required detention
time (depends on the specific modification) and ensure that the acti-
vated sludge and the influent wastewater are thoroughly mixed. Tank
design normally attempts to ensure that no dead spots are created.

8.2.2 aeration

Aeration can be mechanical or diffused. Mechanical aeration sys-
tems use agitators or mixers to mix air and mixed liquor. Some systems
use sparge rings to release air directly into the mixer. Diffused aeration