Section 7. COAL, COKE AND POWER PLANT WASTES
ACHIEVING THE EPA EFFLUENT LIMITATIONS FOR POWER PLANTS:
APPROACHES TAKEN BY UTILITIES IN WISCONSIN
Robert Chiesa, Chemical Engineering Analyst
Sargent and Lundy Engineers
Chicago, Illinois 60603
Suzanne Bangert, Environmental Engineer
Industrial Wastewater Section
Wisconsin Depart, of Natural Resources
Madison, Wisconsin 53707
INTRODUCTION
In 1974 the DNR issued NPDES permits to all electric power utilities requiring achievement of the EPA BPT effluent guideline limitations by July 1, 1977. Although the guidelines require control of a number of pollutants in the discharges (including pH, oil and
grease, chlorine, iron, and copper) the pollutant of major concern at these plants was total
suspended solids (TSS). The effluent guideUnes require monthly average and daily maximum
TSS of 30 and 100 mg/1, respectively, for all process wastewaters and a daily maximum of
50 mg/1 for area run-off.
In response most of the utilities built new wastewater treatment systems (WWTS's) or
substantially modified and improved their existing systems. Two basic approaches were
taken depending on the amount of land available at each plant. Those plants with sufficient
land available for large ash ponds used them as the core of the WWTS to meet the TSS
Umitations. In several cases the ash ponds were already in use prior to 1974 so the WWTS's
only required modifications and additions to meet the EPA limits, but in one case a completely new ash pond system was needed. Those plants with limited land available installed
mechanical WWTS's. In several cases the plants had no treatment so completely new WWTS's
(including extensive modifications to the plants' sewer systems) were needed. In other cases
the existing WWTS's were extensively modified and upgraded.
On July 1, 1977, 24 of the 25 steam-electric power plants in Wisconsin were in substantial compUance with the EPA BPT effluent guideline limits. The other plant completed
its treatment system in October 1977.
DESCRIPTION OF THE POWER PLANTS
AU the plants discussed in this paper are coal-fired, and all generate low-volume wastewaters and bottom ash sluice wastewaters which are the main sources of process wastewater
at coal-fired power plants. Table 1 lists information about each plant and the wastewaters
treated by each plant's WWTS. However none of these plants treat boiler cleaning wastes
(which are very difficult to treat): either the boilers are not cleaned or the boiler cleaning
wastes are coUected and returned to the boilers for incineration.
The three plants with mechanical WWTS's (A,B, and C) are located in urban areas where
little space was available. The three plants with settUng pond WWTS's (X, Y, and Z) are
located on the fringes of urban areas or in rural areas and have space available for large
ash settling ponds.
COMPARISON OF TREATMENT SYSTEM DESIGN
Mechanical Systems
As Table II shows, all the mechanical treatment systems have short detention times and
high hydraulic loading rates, and all must use flocculants to increase the sohds settling rate.
The need for proper flocculation makes the system susceptible to upsets when malfunctions
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