CIVIL ENGINEERING FORMULAS

STORMWATER, WASTEWATER, AND ENVIRONMENTAL PROTECTION 369

SIZING A POLYMER DILUTION/FEED SYSTEM

Depending on the quality of settled secondary effluent, organic polymer addi-
tion is often used to enhance the performance of tertiary effluent filters in a
direct filtration process: see Design of a Rapid Mix Basin and Flocculation
Basin. Because the chemistry of the wastewater has a significant effect on the
performance of a polymer, the selection of a type of polymer for use as a filter
aid generally requires experimental testing. Common test procedures for poly-
mers involve adding an initial polymer dosage to the wastewater (usually 1 part
per million, ppm) of a given polymer and observing the effects. Depending
upon the effects observed, the polymer dosage should be increased or decreased
by 0.5 ppm increments to obtain an operating range.
The gallons per day (gal/day) (L/d) of active polymer required is calculated
using the following:

Active polymer (gal/day) (wastewater flow, Mgd)

(active polymer dosage, ppm) (13.31)

The quantity of dilution water required is calculated using the following:

(13.32)

The quantity of neat polymer required is calculated as follows:

(13.33)

(13.34)

DESIGN OF A SOLID-BOWL CENTRIFUGE
FOR SLUDGE DEWATERING

Centrifuges are commonly used for thickening or dewatering Waste Activated
Sludge (WAS) and other biological sludges from secondary wastewater treat-
ment. In the process, centrifuges reduce the volume of stabilized (digested)
sludges to minimize the cost of ultimate disposal.
The capacity of sludge dewatering to be installed at a given facility is a
function of the size of a facility, capability to repair machinery on-site, and the
availability of an alternative disposal means. Some general guidelines relating
the minimal capacity requirements are listed in Table 13.1 This table is based
on the assumption that there is no alternative mode of sludge disposal and that
the capacity of store solids is limited.

Time required to use one drum of polymer

drum capacity, gal

neat polymer, gal/h

Neat polymer (gal/h)

active polymer, gal/h

% active polymer in emulsion as supplied

Dilution water (gal/h)

active polymer, gal/h

% solution used (as a decimal)