Wastewater Calculations - Mathematics and Statistics for the Environment - page 731

net filter yield, measured in lb/hr/ft 2 , reflects the runtime as well as the downtime of the plate and
frame filter press. To calculate the net filter yield, simply multiply the solids loading rate (in lb/hr/
ft 2 ) by the ratio of filter runtime to total cycle time as follows:

Filter run time
Totalcycle

Netfilteryield = (24.149)

time

■ EXAMPLE 24.115
Problem: A plate and frame filter press receives a flow of 660 gal of biosolids during a 2-hr period.
The solids concentration of the biosolids is 3.3%. The surface area of the plate is 110 ft 2 . If the down-
time for biosolids cake discharge is 20 min, what is the net filter yield in lb/hr/ft 2 ?

Solution: First, calculate solids loading rate, then multiply that number by the corrected time factor:

Biosolids(gph) × 8.34 lb /gal × (% solids 100)

Solids loadingrate =

2

Platearea (ft )

= 330

gph × 8.34 lb/gal × (3.3/100)

2

100 ft

t 2 = 0.83 lb/hr/f

Next, calculate net filter yield, using the corrected time factor:

2

0.83 lb/hr/ft × 2hr

2

0.71 lb/hr/ft 2 Netfilteryield (lb/hr/ft) = =

2.33 hr

24.14.2.2 Belt Filter Press
The belt filter press (Figure 24.9) consists of two porous belts. The biosolids are sandwiched between
the two porous belts. The belts are pulled tight together as they are passed around a series of rollers
to squeeze water out of the biosolids. Polymer is added to the biosolids just before it gets to the unit.
The biosolids are then distributed across one of the belts to allow for some of the water to drain by
gravity. The belts are then put together with the biosolids in between.

24.14.2.2.1 Hydraulic Loading Rate
Hydraulic loading for belt filters is a measure of gpm flow per foot or belt width:

Flow (gpm)
Belt width (ft)

Hydraulic loadingrate(gpm/ft) = (24.150)

■ EXAMPLE 24.116
Problem: A 6-ft-wide belt press receives a flow of 110 gpm of primary biosolids. What is the hydrau-
lic loading rate in gpm/ft?

Solution:

Flow (gpm)
B

110 gpm
6ft

Hydraulic loadingrate(gpm/ft) = = = 18.3 gpm/ft

eltwidth (ft)