1208 URBAN RUNOFF
FIGURE 17 High-intensity mixing (chlorine contact) power
requirements.223344556677101001, 00010 10040501, 000ENERGY USAGE, 1, 000 KWH/YR.INSTALLED HORSEPOWERNUMBER OF DAYS
OF OPERATION
PER YEAR2060equivalent disinfection was obtained using either 3.8 mg/l of
ozone or 5 mg/l of chlorine.
Because of the characteristic intermittent operation asso-
ciated with treatment of CSO, reduction of construction cost
with a potential increase in operating costs often results in
overall minimum costs. In the case of chlorination facilities,
as applied to treatment of CSO, the construction costs associ-
ated with contact basins having conventional contact time of
15–30 min are high and difficult to justify. Therefore, consid-
eration should be given to higher mixing intensities, to make
better usage of the chlorine and/or higher chlorine dosages
and smaller, shorter detention-time contact basins to effect
the same end results. Disinfectant costs for CSO treatment
are higher than those for sewage treatment. This is the result
of smaller total annual disinfectant volume requirements,
increased disinfectant concentration requirements, and higher
unit O&M costs for CSO treatment facilities. These costs
could be reduced by using the facilities in conjunction with
dry-weather flow treatment plants, whenever possible. Curves
comparing generation and feed costs for chlorine gas, chlorine
dioxide, and hypochlorite generation disinfection systems for
CSO have been developed and are presented in Figure 15.
These costs include manufactured equipment, labor, piping,
housing, electrical and instrumentation, and miscellaneous
items; no allowance for land was included. Capital and oper-
ating costs for several CSO and stormwater disinfection facili-
ties are presented in Table 38.
As previously mentioned, conventionally long contact
times may not be economical. Short-term contact times with
more intense mixing, using a basin and mixer similar tothose used in coagulant mixing, can effect the same disin-
fection results. Construction cost curves for high-intensity
mixing/chlorine contact basins are presented in Figure 16.
Power requirement curves, for high-intensity mixing, are
presented in Figure 17.
The capital costs for different disinfection agents and
methods resulting from the Philadelphia study are shown in
Table 39. The capital costs for ozone generation are usually
the highest of the most commonly used processes. Ozone
operation costs are very dependent on the cost of electricity
and the source of the ozone (air or pure oxygen).REFERENCESSECTION 1EPA-600/2-75-004, “Contributions of Urban Roadway Usage to Water Pol-
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EPA-600/2-79-161, “Demonstration of Nonpoint Pollution Abatement
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Clyde Consultants, San Francisco, CA, August 1979 (NTIS PB 80–
108988).
EPA-600/8-80-035, “Urban Stormwater Management and Technology:
Case Histories,” W.G. Lynbard, et al., Metcalf & Eddy, Inc., Palo Alto,
CA, August 1980 (NTIS PB 81 107153).
EPA-R2-72-81, “Water Pollution Aspects of Street Surface Contami-
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