OPERATING EXPERIENCE WITH AN
INTEGRATED POWER PLANT WASTEWATER
TREATMENT SYSTEM
Robert Chiesa, Senior Chemical Analytical Engineer
Sargent and Lundy Engineers
Chicago, Illinois 60603
Paul D. Schumacher, Chemist
Wisconsin Electric Power Company
Milwaukee, Wisconsin 53201
Utilities were once able to design and operate power plants with little regard given to
wastewater treatment. Large ash ponds or mechanically cleaned ash pits were often all
that were required to meet the discharge requirements. However, since the U.S. Environmental Protection Agency (EPA) promulgated New Source Performance Standards (NSPS)
for discharges from new power plants under the federal Clean Water Act, treatment of
power plant wastes has become much more complex. This paper describes the design and
operation of an integrated wastewater treatment system (WWTS) used to treat the chemical
wastes from a coal-fired power plant.
In 1980 an integrated WWTS began operation at the Pleasant Prairie Power Plant of
Wisconsin Electric Company (WEPCo). The power plant consists of two new coal-fired
cycling units. The basic process design of the WWTS was performed by Sargent & Lundy
(S&L) with detailed equipment design performed by the WWTS equipment manufacturer.
The WWTS was designed to have the flexibility to treat the chemical wastes (i.e., metal
cleaning wastes, low-volume wastes and material storage runoff) at this plant to achieve
the EPA NSPS effluent limitations applicable to a new power plant. The WWTS was also
designed to be highly automated, with minimal operation and maintenance required by
plant personnel. This was an important consideration because the WWTS is remote from
the main plant, and continuous operator attention was not considered to be cost-effective.
This plant has most of the typical waste streams associated with a modern coal-fired power
plant, and its WWTS is typical of other integrated WWTS. A review of its performance
since startup will give an indication of the successes (and difficulties) encountered in designing and operating an integrated WWTS for a new coal-fired power plant.
PURPOSE OF AN INTEGRATED WWTS
An integrated WWTS is designed to have the flexibility to treat all the chemical wastes
generated by a coal-fired power plant. Power plant wastewaters vary drastically in flowrate
and frequency of generation, as well as the type and degree of treatment required. The EPA
has established effluent limitations on various pollutants for three different categories of
wastes from power plants [11. Table I lists the three categories and the applicable effluent
limitations associated with each category.
Metal cleaning wastes are generated by the scheduled cleaning of major power plant
equipment, such as the boilers, air heaters, and precipitators, during unit outages. These
wastes are the most difficult power plant wastes to treat because they can be highly acidic,
contain high concentrations of dissolved iron and copper, and contain appreciable amounts
of total suspended solids. Boiler cleaning wastes are especially difficult to treat. The boiler
chemical cleaning solutions often contain chelating agents which are used to improve the
removal of iron and copper deposits in the boiler and preboiler piping. The metal chelates
formed can be highly stable and must be broken before the metals can be removed from
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