Wastewater Calculations - Mathematics and Statistics for the Environment - page 735

Solids
discharge
zone

Drying
zone

Conveyor

Solids pickup
zone

Sludge vat

FIGURE 24.10 Vacuum Filter.

■ EXAMPLE 24.123
Problem: Digested biosolids are applied to a vacuum filter at a rate of 70 gpm, with a solids concen-
tration of 3%. If the vacuum filter has a surface area of 300 ft 2 , what is the filter loading in lb/hr/ft 2 ?

Solution:

Biosolids( gpm)60min/hr × × 8.34 lb/gal × (% solids 100)

2 =

Filterloading rate (lb/hr/ft)

2

Su rface area (ft )

70 gpm × 60 min/hr × 8.34 lb/ gal 3/100) ×

=

2

300 ft

2

= 3.5 lb/hr/ft

24.14.3.2 Filter Yield
One of the most common measures of vacuum filter performance is filter yield. It is the lb/hr of dry
solids in the dewatered biosolids (cake) discharged per square foot of filter area. It can be calculated
using Equation 24.157:

Wet cakeflow(lb/ hr)%Solids in cake 100)

Filter area (ft )

× (

2 =

Filteryield (lb/hr/ft) (24.157)

2

■ EXAMPLE 24.124
Problem: The wet cake flow from a vacuum filter is 9000 lb/hr. If the filter areas is 300 ft 2 and the
percent solids in the cake is 25%, what is the filter yield in lb/hr/ft 2 ?

Solution:

Wet cakeflow(lb/ hr)%Solids in cake 100)

Filter area (ft )

× (

2 =

Filteryield (lb/hr/ft)

2

9000 lb/hr 25/100)
300 ft

×

2

= = 7.5 lb/hr/ft

2

24.14.3.3 Vacuum Filter Operating Time
Use Equation 24.157 to calculate the vacuum filter operating time required to process a given lb/day
solids. The vacuum filter operating time is the unknown factor, designated by x .