Therefore, a conditioning tank should be selected with a 7200 L or 7.2 m3

(1900 gallon) working capacity. This conditioning tank should also be equipped with a

mixer and level switches to control the operation of the sludge and conditioning chemi-

cal metering pumps.

5-3.2.3.7 **Compute the Size of the Sludge Feed Pumps to the Filter Presses**. Each

filter press will be equipped with one sludge operating feed pump and one standby

pump. The total quantity of conditioned sludge plus chemical solution to the filter

presses follows:

Sludge quantity = 112,000 L/d (29,540 gpd)

Water in lime at 10% solution = [280 kg/d] / [(0.1 x 1 kg/L)] = 2800 L/d (740 gpd)

Water in polymer at 5% solution = [112 kg/d] / [(0.05 x 1 kg/L)] = 2240 L/d (600 gpd)

Total quantity to be pumped = (112,000 + 2800 + 2240) L/d = 117,040 L/d (30,880 gpd)

Pumping rate for each pump when 4 filter units are operating = [117,040 L/d]/[(4 pumps) x (8

cycles/day) x (1200 s/cycle)] = 3 L/s (50 gpm)

Therefore, the total required pumping capacity for each operating and

standby pump is 3 L/s (50 gpm) at a filter press pressure of 345 kPa (50 psig). How-

ever, prior to selection of the appropriate pump, any additional system head losses, plus

safety factor requirements, should be determined and combined with the required filter

press pressure to determine the overall head requirements. Once this is determined,

manufacturers' catalogs should be obtained and an appropriate pump selected.

5-3.2.4

5-3.2.4.1 **Compute the Total Sludge Cake Solids**. The filter cake contains sludge

solid, lime, and polymers. This example will assume that 75% of the conditioning

chemicals are incorporated into the sludge cake and that the dewatering facility

provides 95% solids capture.

Sludge solids in cake = 0.95 x 5600 kg/d = 5320 kg/d

Lime solids in cake = 0.75 x 280 kg/d = 210 kg/d

Polymer solids in cake = 0.75 x 112 kg/d = 84 kg/d

Total dry solids in sludge cake = 5620 kg/d (12,370 lb/d)

5-3.2.4.2 **Compute the Volume of Sludge Cake and Required Storage**. The sludge

cake has a bulk density of 1120 kg/m3 (70 lb/ft3). This example will assume that the

sludge will be discharged directly into a hopper for direct dumping into transport trucks

for offsite disposal, and 4 days of sludge cake storage will be provided.

5-18

Integrated Publishing, Inc. |