TABLE 2. Typical Dosing Rates for Trickling Filters
Organic loading Ib BOD 5 /! O^3 Dosing rate,
ft^3 -d (kg/m^2 -d) in/pass (cm/pass)
<25 (122.2) 3 (7.6)
50(244.3) 6(15.2)
75(366.5) 9(22.9)
100 (488.7) 12 (30.5)
150(733.0) 18(45.7)
200 (977.4) 24 (60.9)(Wastewater Engineering: Treatment, Disposal, and Reuse, Metcalf
& Eddy, 3rd Ed.)where n = Rotational speed of distributor (rpm)
QT = Total applied hydraulic loading rate (gal/min-ft^2 ) (L/s-m^2 ) = Q + QR
Q = Influent wastewater hydraulic loading rate (gal/min-ft^2 ) (L/s-m^2 )
QR = Recycle flow hydraulic loading rate (gal/min-ft^2 ) (L/s-m^2 ) Note: recycle is as-
sumed to be zero in this example
A = Number of arms in rotary distributor assembly
DR = Dosing rate (in/pass of distributor arm)
Assuming two distributor arms (two or four arms are standard), and using values from
above, the required rotational speed is:
1.6(0.99 gal/min-ft^2
n =
,^,^n- / T" = °-
058 1
P
111
(2)(13.7 in/pass)This equates to one revolution every 17.2 minutes.
SIZING OFA ROTARY-LOBE SLUDGE PUMP
A municipal wastewater treatment facility produces approximately 6,230 gal/day (23.6
m^3 /d) of aerobically digested sludge at 5 percent solids. The digested sludge is pumped to
a sludge dewatering facility which is operated 4 h/d, 7 d/wk; 1000 ft (304.8 m) of 3 in
(76.3 mm) equivalent length pipe exists between the aerobic digester and the dewatering
facility. The equivalent length of pipe includes all valves, fittings, discharge pipe, and
suction pipe lengths in the sludge piping system. The static head on the sludge pump is 10
feet (3.0 m). Size a rotary-lobe pump transfer sludge from the digester to the dewatering
facility, including pump discharge and head condition, rpm and motor horsepower (kW).
Calculation Procedure:- Find the flow rate required for the sludge pump
A schematic of the sludge handling system is illustrated in Fig. 9. Rotary-lobe pumps are
positive-displacement pumps in which two rotating synchronous lobes push the fluid
through the pump. Although these types of pumps are advertised as self-priming, they are