Wastewater Calculations - Mathematics and Statistics for the Environment - page 720

■ EXAMPLE 24.93
Problem: What is the volatile matter in pounds per day?

Solution:

Volatile matter (lb/day) = 13,331 lb/day × 0.66 = 8798 lb/day

24.11.6.9 Pounds of Solids per Pounds of Volatile Solids per Day
If we wish to calculate the pounds of solids or the pounds of volatile matter removed per day, the
individual equations demonstrated above can be combined into single calculations:

Solids (lb/day) = Pump time(min/cycle)Frequ × ency (cycles/day)

(24.125a)

× Rate (gpm) × 8.34 lb/gal × Solids %

Volatile matter (lb/day) = Pump time (min/cyc le)Frequency(cycles/day) ×

(24.125b)

× Rate (gpm) × 8.34 lb/gal × %Solids%Volatile matter ×

■ EXAMPLE 24.94

Solids = 15 min/cycle × 24 cycles/day × 120 gpm × 8.34 lb/gal × 0.0370 = 13,331 lb/day

Volatile matter = 15 min/cycle × 24 cycles/day × 120 gpm × 8.34 lb/gal × 0.0370 × 0.66 = 8798 lb/day

24.12 BIOSOLIDS THICKENING
Biosolids thickening (or concentration) is a unit process used to increase the solids content of the
biosolids by removing a portion of the liquid fraction. In other words, biosolids thickening is all
about volume reduction. Increasing the solids content allows more economical treatment of the
biosolids. Biosolids thickening processes include the following:

• Gravity thickeners
• Flotation thickeners
• Solids concentrators

Biosolids thickening calculations are based on the concept that the solids in the primary or sec-
ondary biosolids are equal to the solids in the thickened biosolids. The solids are the same. It is
primarily water that has been removed to thicken the biosolids and result in a higher percent solids.
In this unthickened biosolids, the solids might represent 1 to 4% of the total pounds of biosolids, but
when some of the water is removed those same solids might represent 5 to 7% of the total pounds
of biosolids.

Note: The key to biosolids thickening calculations is that solids remain constant.

24.12.1 g ravity /d issolved a ir F lotation t hiCKener C alCulations
Biosolids thickening calculations are based on the concept that the solids in the primary or second-
ary biosolids are equal to the solids in the thickened biosolids; that is, assuming a negligible amount
of solids are lost in the thickener overflow, the solids are the same. Note that the water is removed
to thicken the biosolids and results in higher percent solids.