Solids Handling - Wastewater Operators - page 382

10.6.2.9.1 required Seed volume in gallons

Seed Volume (gal) = Digester Volume × % Seed (10.21)

 Example 10.21

Problem: The new digester requires a 25% seed to achieve normal opera-
tion within the allotted time. If the digester volume is 266,000 gal, how
many gallons of seed material will be required?

Solution:

Seed Volume = 266,000 gal × 0.25 = 66,500 gal

10.6.2.9.2 volatile acids-to-alkalinity ratio

The volatile acids-to-alkalinity ratio can be used to control opera-
tion of an anaerobic digester:

Volatile AcidsConcentration

Alkalinity Concentration

Volatile Acids-to-AlkalinityRatio = (10.22)

 Example 10.22

Problem: The digester contains 240 mg/L volatile acids and 1860 mg/L
alkalinity. What is the volatile acids-to-alkalinity ratio?

Solution:

240mg/L
1860 mg/L

Ratio = = 0.13

Note: Increases in the ratio normally indicate a potential change in the
operation condition of the digester as shown in Table 10.6.

10.6.2.9.3 Sludge retention Time

Sludge retention time (SRT) is the length of time the sludge remains
in the digester:

Digester Volume (gal)
Sludge Volu

SRT(days) = (10.23)

me Addedper Day(gpd)

 Example 10.23

Problem: Sludge is added to a 525,000-gal digester at the rate of 12,250
gpd. What is the sludge retention time?