Polymer feed rate in gal/h is calculated using the following:polymer feed rate Ib/h)
Polymer feed rate (gal/h) = ,0<t. lL/ fw Wft/ : :—r
(8.34 lb/gal)(s.g.)(% polymer concentration)where s.g. = specific gravity of the polymer solution
% polymer concentration expressed as a decimal
Using values defined previously:
T» i * A + /- I/UN 5.0 Ib/h
Polymer feed rate (gal/h) = (8 34 lb/gal)(1 0)(025)= 2.4 gal/h of 25% polymer solution (0.009 L/h)The polymer feed rate is used to size the polymer dilution/feed equipment required for the
sludge dewatering operation.
Related Calculations. Selection of units for dewatering facility design is de-
pendent upon manufacturer's rating and performance data. Several manufacturers have
portable pilot plant units, which can be used for field testing if sludge is available. Waste-
water sludges from supposedly similar treatment processes but different localities can dif-
fer markedly from each other. For this reason, pilot plant tests should be run, whenever
possible, before final design decisions regarding centrifuge selection are made.
SIZING OFA TRAVELING-BRIDGE FILTER
Secondary effluent from a municipal wastewater treatment facility is to receive tertiary
treatment, including filtration, through the use of traveling bridge filters. The average dai-
ly flow rate is 4.0 Mgd (2778 gal/min) (15,140 m^3 /d) and the peaking factor is 2.5. Deter-
mine the size and number of traveling bridge filters required.
Calculation Procedure:- Determine the peak flow rate for the filter system
The traveling bridge filter is a proprietary form of a rapid sand filter. This type of filter is
used mainly for filtration of effluent from secondary and advanced wastewater treatment
facilities. In the traveling bridge filter, the incoming wastewater floods the filter bed,
flows through the filter medium (usually sand and/or anthracite), and exits to an effluent
channel via an underdrain and effluent ports located under each filtration cell. During the
backwash cycle, the carriage and the attached hood (see Fig. 5) move slowly over the fil-
ter bed, consecutively isolating and backwashing each cell. The washwater pump, located
in the effluent channel, draws filtered wastewater from the effluent chamber and pumps it
through the effluent port of each cell, forcing water to flow up through the cell thereby
backwashing the filter medium of the cell. The backwash pump located above the hood
draws water with suspended matter collected under the hood and transfers it to the back-
wash water trough. During the backwash cycle, wastewater is filtered continuously
through the cells not being backwashed.