17 DEC 2003
Minimum tank volume required:
41,328 L 15,984 L = 25,334 L
(10,900 gal. 4200 gal. = 6700 gal.)
C-1.9.5 A 25,400-L (7000-gal.) equalization tank is minimum; use 30,000-L (8000-
gal.) tank for a safety margin.
Transfer Pump from Equalization Tank to Upflow Continuous Backwash
Filter. Design system piping to keep flow velocity under 1.5 m/s (5 fps) to minimize po-
tential for water hammer. From piping tables, at a flow of 2.2 L/s (35 gpm), use 5.0 cm
(2-in.) diameter piping. Flow velocity is 1.1 m/s (3.6 fps) at 2.2 L/s (35 gpm) for 5.0 cm
(2-in.) schedule 40 pipe. At that flow velocity, assume a pressure drop for valves and
fitting of 10.34 kPa (1.5 psi). The total from that transfer pump across the continuous
backwash filter is equal to the sum of the piping loses and the loss across the filter,
based on information contained in vendor literature or
44.5 kPa + 10.3 kPa = 54.8 kPa ~ 55 kPa.
(6.45 psi + 1.5 psi = 7.95 psi ~ 8 psi).
Size the transfer pump to deliver 2.2 L/s at 0.56 kPa (35 gpm at 8 psi). The
designer should note that the head loss across the filter would vary with the manufac-
Return Flow Pump from Thickening Tank to Equalization Tank. Return
flow rate: 3.8 L/s (60 gpm), assume 6.1 m (20 ft) elevation head or
6.1 m x (0.099 kg/cm2)/m = 0.604 kg/cm2 = 59.23 kPa.
(20 ft x 0.43 psi/ft = 8.6 psi)
Using 5.0 cm (2-in.) pipe, we assume a pressure drop through valves and fit-
ting of 31.4 kPa (4.5 psi) for a total pressure drop of
60.8 kPa + 31.4 kPa = 92.2 kPa.
(8.6 psi + 4.5 psi = 13.1 psi)
Size the pump for 3.78 L/s at 92.2 kPa (60 gpm at13.1 psi).
The groundwater treatment system
following equipment. Figure C-1 is a flow diagram for the system.
1 - Equalization tank: 30,000 L (10,000-gal.).
1 - Transfer pump: 2.2 L/s at 55 kPa (35 gpm at 8 psi).
2 - Chemical feed systems for polymer (1 optional).