Wastewater Biosolids Dredging

Dredging a wastewater pond or lagoon can be performed with multiple methods.  Mechanical dredging can excavate the biosolids from the lagoon from the shoreline or even a barge mounted excavator.  However, the biosolids typically contain a high percentage of water creating issues when handling them once they are excavated.  Berms to contain the solids or drying beds can be utilized but these methods are not very efficient.  Another option is to allow the pond or lagoon to dry out by taking it offline during a suitable time of the year with dry weather and allowing the solids to dry in place before being excavated.  The limiting factors are still the fact that you cannot use that pond or lagoon and that the sludge may not dewater fully with the method.

The preferred method for dredging a pond or lagoon is generally hydraulic dredging with subsequent dewatering of the sludge.  Portable hydraulic dredges are available in almost any size from remote control units to larger dredges that are assembled in sections.  The use of a hydraulic dredge will enable removal of the sludge without lowering the water level and can enable the plant to remain functioning and online with some adjustments.  Typically an auger cutterhead is used with protective guides or wheels for ponds or lagoons that have a liner along the bottom.  These devices will not allow the auger to tear or rip the liner in place but physically preventing it from reaching the bottom.  An auger cutterhead is ideal for making wide passes through the biosolids and transferring them into the pump.  The dredge then pumps the slurry, a mixture of sludge and water, through pipeline which is usually 6”, 8”, or 10” in diameter for most projects.  The operator may have to add water to the pond if the dredging process does not return water back into the same pond or lagoon.  The most critical step and method in cleaning out your pond or lagoon is the dewatering process.  This occurs at the discharge of the pipeline from the dredge.

Once the sludge is removed from the wastewater pond or lagoon it is ready for disposal.  Many times one requirement is for the material to pass a paint filter test.  But where do you dispose of biosolids?  Generally speaking, most wastewater facilities are already disposing of some portion of their solids.  The EPA classifies many biosolid into classes that determine the options for disposal.  Most biosolids are dredged, dewatered, and disposed of at a landfill.  Alternative options include composting for use in soil amendments, land application, and incineration.  Most of the alternatives involve an extensive look into the regulatory aspect though and certain risks along with any method, even if from a public perception.  Alternative methods may become more available as landfills are refusing to take sludge and biosolids for disposal.  This leads to additional transport costs and limited options for disposal.  Regardless, disposal must be considered prior to beginning a project.