Civil Engineering Reference
In-Depth Information
bedrock), ground slope, and land availability help determine the monofilling
method that is selected.
Environmental Considerations
The potential for leaching of metal components and other contaminants in the
residuals into groundwater supplies must be addressed.
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Lining
Technology-based standards require a composite liner system be installed that
consists of an upper geomembrane liner and a lower compacted-soil liner to con-
trol the escape of leachate into groundwater.
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Land Application
The options for land application of WTP residuals include agricultural use, sil-
vicultural application, application for reclamation to disturbed and marginal lands,
and disposal to dedicated lands.
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The application of WTP residuals may ben-
eficially modify soil properties while recycling residual components. The possible
disadvantages of land application of WTP residuals include an increase in the
concentration of metals in the soil and possibly in groundwater; adsorption of soil
phosphorus by water treatment residuals, decreasing the productivity of the soil;
excessive application of nitrogen, resulting in the transport of nitrate to ground
water; and possible effects caused by the application of poorly crystallized solids
of aluminum.
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A simplified planning procedure for land application is presented
in Figure 23-25.
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Use as Building or Fill Material
Alum sludge has been suggested for use as a
plasticizer in the ceramics industry, as a constituent of refractory bricks, and as a road-
stabilizing agent. In Atlanta, dewatered alum sludge from the Hemphill alum sludge
treatment facility is transported to a residential building site, where it is used as fill.
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Sludge cake is spread and compacted by a bulldozer to depths as great as 6 feet (1.8
m). No problems have been reported with driving loaded trucks over the compacted
sludge cake.
Liquid Residual Alternatives
There are several potential sources of liquid waste streams from a conventional water
treatment plant.
Major Waste Streams
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Spent-filter backwash water
Filter-to-waste water
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Other Waste Streams
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Presedimentation basin blowdown sludge
Sludge thickener supernatant
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Sludge lagoon overflow
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Filtrate from plate and frame filter presses
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Pressate from belt filter presses
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Centrate from centrifuges
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Leachate from sand drying beds
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