URBAN RUNOFF 1203
TABLE 30
Summary of capital, operation and maintenance costs for biological treatment alternatives (ENR = 5,000)Project location Type of biological treatment Peak plant
capacity
(Mgal/d)Construction
cost ($1000)Cost/
capacity
($/Mgal/d)Cost/
tributary area
($/acre)Annual O&M
($/1,000 gal.
except as noted)Kenosha, WI Contact stabilization 20 3410 170,000 2900 34.5
Milwaukee, WI* Rotating biological contactor 4.3 747 173,000 21,400 11.0
Mount Clemens, MI
Demonstration system Aerated treatment lagoons 64 1,607 25,000 7,600 50.0
Citywide system Storage/aerated treatment lagoons 260 14,343 55,000 9,800 47.5
New Providence, NJ† High-rate trickling filter 6 1,188 198,000 — 30.7
Shelbyville, IL
Southeast site Oxidation lagoon 28 108 3,900 2,790 3,820/yr‡
Southwest site Storage and facultative lagoons 110 844 7,700 1,900 14,460/yr‡
Springfield, IL Oxidation lagoon 67 440 6,500 200 5,260/yr*^ Includes estimate of final clarifier.
† Includes plastic media trickling filter, final clarifier, plus one-half of other costs.
‡ Based on estimated man-day labor requirements.These costs can be used as a preliminary guide, but detailed
analyses should be performed to compare and evaluate
biological treatment alternatives with other methods of treat-
ment and control. Initial capital investments of integrated
dual-use facilities can be reduced by apportioning part of
the costs to the dry-weather facility. The cost reduction is
in proportion to the net benefit that the wet-weather facil-
ity provides to the overall treatment efficiency during dry-
weather periods.6 ADVANCED TREATMENTHigh Gradient Magnetic SeparationHigh gradient magnetic separation (HGMS) is a new treatment
technology applied to CSO management. In its simplest form,
the high gradient magnetic separator consists of a canister
packed with a fibrous ferromagnetic material that is magne-
tized by a strong external magnetic field (coils surround the
canister). An iron frame increases the efficiency of the electro-
magnetic coils. The device operates in a sequence of feed and
flush modes.
The magnetic particles are trapped on the edges of the
magnetized fibers while the nonmagnetic particles and slurry
pass through the canister. The matrix offers only a small
hydraulic resistance to the feed flow, occupying less than 5%
of the canister volume (95% void volume). When the matrix
has become loaded with magnetic particles, the particles are
easily washed from the matrix by reducing the magnetic field
to zero and opening valves and backflushing. High gradient
magnetic separation may also be used to remove nonmag-
netic contaminants from water. This is accomplished by bind-
ing finely divided magnetic seed particles, such as magnetic
iron oxide (magnetite), to the nonmagnetic contaminants,
thus creating a “magnetic handle” (“indirect filtration” or“seeded water treatment”). Binding of the magnetic seed
is accomplished in two general ways: (1) adsorption of the
contaminant to magnetic seed and (2) chemical coagulation
(alum). Particles ranging in size from soluble through settle-
able (0.001 μ ) may be removed with this process. Design
parameters for HGMS are presented in Table 31.
Magnetic separation can provide the rapid filtration of
many pollutants from water, with a small expenditure of
energy. Removal is much more efficient than with sedimen-
tation because the magnetic forces on fine particles may be
many times greater than gravitational forces. To date, only
bench scale tests and a pilot-plant scale system of 1–4/min
(0.26–1.06 gal/min) have been operated. Typical pollutant
removals are shown in Tables 32, 33 and 34.
Costs of HGMS have been evaluated for a 94,625-m^3 /d
(25-Mgal/d) facility and are summarized in Table 35.
Capital costs include pre-treatment, chemical addition,
thickening and dewatering equipment, pumps, backflush
system, instrumentation, and disinfection system. Operation
and maintenance costs include chemicals, labor, electrical
utilities, and maintenance.Powdered Activated Carbon-Alum CoagulationSeveral combined sewage treatment demonstration projects
have evaluated the benefits of chemical aids to process oper-
ations, but only one pilot operation representing a complete
physical–chemical treatment system has been implemented.
It was demonstrated at a 379-m^3 /d (100,000-gal/d) pilot unit
in Albany, New York. In this project, raw municipal sewage
and CSO were mixed with powdered activated carbon to
remove dissolved organics. Alum was then added to aid in
subsequent clarification. Addition of polyelectrolytes was
followed by a short flocculation period. Solids were separated
from the liquid stream by gravity settling, and the effluentC021_002_r03.indd 1203C021_002_r03.indd 1203 11/23/2005 9:45:49 AM11/23/2005 9: