Section 11. STEEL AND FOUNDRY WASTES
EXPERIENCES WITH LOW HEAD FILTRATION OF
STEEL MILL WASTEWATERS
Thomas J. Galatro, Development Engineer
Kathleen W. Simmers, Development Engineer
Environmental Elements Corporation
Subsidiary of Koppers Company
Baltimore, Maryland 21076
The Environmental Elements Corporation, a wholly owned subsidiary of Koppers Company Incorporation, is the manufacturer of the low head Automatic Backwash, or ABW®
Filter. Numerous ABW installations are found in municipal and industrial fdtering systems to
provide potable water, polished tertiary effluent and recycled wastewater for manufacturing
plants. A substantial number of fdters have been employed in the following appliations:
1. the pulp and paper industry in filtering pre-treated influent process water and wastewater;
2. in cooling-tower side-stream filtration processes where unattended, automatic operation
is required.
3. in petroleum refineries to polish oily wastewater from oil waste separators;
4. in the chlorine caustic industry where these filters are used as process equipment for
polishing of treated sodium chloride brines and
5. in the metal finishing industry to remove metal hydroxide precipitates and cutting oils
from wastewater.
A mobile ABW Filter Pilot Unit was recently used to demonstrate the abdity of a low
head filter to process wastewaters typically found in steel mills. Five different steel manufacturing processes were selected for the performance evaluation. The process wastewater
sources were: (a) tube works scale pit; (b) primary bar and structural lagoons; (c) continuous
caster scale pit; (d) terminal treatment plant clarifiers; and (e) hot strip mill finishing side
scale pit.
To be acceptable, the treatment of the waste at each test location had to be accomplished
with neither the suspended solids nor the od and grease content of the fdtrate exceeding
5 mg/1. The steel plant personnel were responsible for the daily operation of the pilot unit
and the recording of data. Environmental Elements Corporation personnel acted as test
consultants. A detailed analysis of the operating data is in process. This paper discusses the
general results, trends, and operating characteristics which were observed during testing.
FILTER OPERATION
The low head ABW Filter uses a granular media to remove waste particles from a stream,
as shown in Figure I. The filter bed is divided across its width into individual 200 mm (8 in.)
wide fdter cells. Porous plates in each cell form the top of the underdrain channel and
support the media bed, which is usually 280 mm (11 in.) of 0.6 mm effective size silica sand,
with a uniformity coefficient less than or equal to 1.5. This type of media support system
eliminates the need for grading the filter bed. During filtration, wastewater is introduced
to the filter through influent ports above the media bed. It then passes through the sand
and porous plates to the underdrain and exits through effluent ports into the effluent channel. The 280 mm (11 in.) of media is naturally graded during backwash with the smallest
granules at the top of the bed. When the wastewater is filtered, the waste particles are
removed in the top few centimeters of media bed. The accumulation of waste particles
forms a "schmutzdecke," which enhances the filtration process. The filter is backwashed
before the headloss reaches more than 300 mm (12 in.) of water column to prevent the
solids from being forced deep into the media bed. Although the filter cycles are shorter
than in a conventional deep bed filter, the smaller quantity of accumulated solids and the
shallow penetration of solids into the bed permit the use of less total backwash water, and
lower backwash flow rates.
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