57    LAND APPLICATION OF WATER PLANT SLUDGES
Brian A. Dempsey, Assistant Professor
James DeWolfe, Graduate Research Assistant
Douglas Hamilton, Graduate Research Assistant
Yuanjyh Lee, Graduate Research Assistant
Roni Liebowitz, Graduate Research Assistant
Department of Civil Engineering
Herschel A. Elliott, Associate Professor
Department of Agricultural Engineering
The Pennsylvania State University
University Park, Pennsylvania 16802
INTRODUCTION
Most municipal and industrial waters are produced by conventional treatment processes, which
include the addition of a coagulant during a rapid mixing period, flocculation of solids during a slow
mix period, and then separation of the solids by means of sedimentation and filtration processes. Two
decades ago most of the sludges produced during conventional water treatment were returned to a
watercourse without further treatment. This often resulted in severe detrimental impact to the watercourse, since the sludges contained both the original solids from the watercourse plus new solids
generated during treatment and also because the disposal was irregular, with large flows during
backwash of the filter or from intermittent cleaning of sedimentation basins. In many cases the sludge
was disposed into a smaller watercourse than the source of the water. As a result, the EPA decided
that the sludges from municipal and industrial water treatment must be treated in a responsible
fashion.
Presently, the favorite options for disposal of water plant sludges (WPS) are lagoon storage (usually
a temporary solution), landfill (which requires substantial dewatering and may present liability problems, especially for co-disposal), and dumping into sanitary sewers (which often creates an undesirable load on sewage treatment facilities). Land disposal is another option but one that has been used
infrequently. State governments usually have primacy regarding the land application of WPS; most
state governments are experienced regarding land application of sewage sludge but do not know how
to deal with land application of WPS.
The lack of regulatory expertise regarding WPS is not surprising. Basic data about the chemical
nature of WPS are quite sparse. The literature contains substantial information regarding dewatering
of WPS, but almost no data regarding the elemental composition and speciation, the phytotoxicity or
microbial toxicity of WPS, and the effects of WPS on the physical and nutrient status of soil.
These issues are addressed in this chapter. The goal of this work is to add to the scientific data base
regarding WPS so that the reactivity of the sludge (especially, in this case, during land application) can
be predicted. More specifically, the following issues are addressed:
• What is the impact of WPS on the nutrient status of the soil?
• What are the concentrations and reactivities of trace metals in WPS?
• What are the other issues that should be used to predict proper loadings of WPS on soils?
A COMPARISON OF WATER PLANT SLUDGE AND SEWAGE SLUDGE
Sewage sludge contains substantial reactive concentrations of nitrogen and phosphorus, trace
elements, and tilth-building organic material. As a result sewage sludge has been used as a soil
amendment for millennia. The biggest historical problem has been the spread of pathogens. Since the
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