Wastewater Calculations - Mathematics and Statistics for the Environment - page 675

Compute the outlet weir overflow rate, w l :

3

3600 m/day
8m

3

w l = = 150 m/(day m) ⋅ = 12,100 gal/day

× 3m

24.4 BIOSOLIDS PUMPING CALCULATIONS
Determination of biosolids pumping (the quantity of solids and volatile solids removed from the
sedimentation tank) provides accurate information necessary for process control of the sedimenta-
tion process.

Solids Pumped = Pump Rate (gpm) × Pump Time (min/day) × 8.34 lb/gal × % Solids (24.17)

Volatile Solids (lb/day) = Pump Rate × Pump Time × 8.34 × % Solids × % Volatile Matter (24.18)

■ EXAMPLE 24.19
Problem: A biosolids pump operates 30 min/hr. The pump delivers 25 gal/min of biosolids.
Laboratory tests indicate that the biosolids are 5.3% solids and 68% volatile matter. How many
pounds of volatile matter are transferred from the settling tank to the digester? Assume a 24-hour
period.

Solution:
Pump time = 30 min/hr
Pump rate = 25 gpm
%Solids = 5.3%
%Volatile matter = 68%

Volatile Matter = 25 gpm × (30 min/hr × 24 hr/day) × 8.34 lb/gal × 0.053 × 0.68 = 5410 lb/day

24.4.1 p erCent t otal s olids C alCulations
Problem: A settling tank biosolids sample is tested for solids. The sample and dish weigh 73.79 g.
The dish alone weighs 21.4 g. After drying, the dish with dry solids weighs 22.4 g. What is the per-
cent total solids (%TS) of the sample?

Solution:

Sample + dish 73.79 g Dish + dry solids 22.4 g

Dish alone -21.40 g Dish alone -21.4 g

52.39 g 1.0 g

(1.0 g ÷ 52.39 g) × 100% = 1.9%

24.4.2 bod and ss r emoval C alCulations
To calculate the pounds of BOD or suspended solids removed each day, we need to know the mg/L
BOD or SS removed and the plant flow, then we can use the mg/L to lb/day equation:

SS removed = mg/L × MGD × 8.34 lb/gal (24.19)