CCRs including ash can considerably cut down on the safety and produtivity of coal power plants. Coal ash can be removed through dredging with a cutter head and pump that is connected to a flexible pipe. The material is then pumped to another area for proper settling and dewatering. Mechanical dredging with an excavator can be performed as well. The determination of the best method is often limited by access to the pond or lagoon from the shoreline and where the coal ash or fly ash needs to be disposed of. If the dredge can pump the ash directly into the disposal area, that method may be most effecieint. If the excavator can load trucks along the shoreline or a peninsula for offsite disposal then that method may be the best way to remove coal ash.
Yes, geotextile tubes are a great method to dewater coal ash as it is pumped or dredged from a pond or lagoon. The tubes allow for the material to be safely stored, without the risk of eroding, until the material is dry enough for final disposal.
Small hand operated dredges can be purchased for as little as $15,000, but they are only effective for limited types of projects and sediment. The smaller dredge barges can be purchased for $100,000 to $150,000. As you increase in size and effectiveness, most portable dredges cost between $500,000 and $2,000,000. The cost only increases for dredges bigger and with more features extending through the millions and for the largest dredges into the tens of millions. Auxiliary equipment and pipeline are an additional expense that needs to be considered as well in the cost of purchasing a dredge.
Yes, dredges can be equipped with guides or wheels to protect the auger or cutterhead from damaging the liner while pumping sludge or sediment.
Sludge can be tested for approval for land application or landfill disposal. Some sludges can be used for soil amendments as well. Sludges have been incinerated for disposal and even rarely as a feedstock for energy production.
Dredging is the method to remove sediment, silt, and muck from a lake, pond, or lagoon. You can dig the dirt out with an excavator, or you can pump it out with a dredge.
You can measure the depth of water and sludge in a lagoon using a Sludge Judge®. A sludge judge will allow you to measure the depth of water down to the surface of the sludge and then push through it to actually sample the sludge as well. You can also use a rod or pvc pipe with markings to find the depth from the water to the top of the sludge. The depth of sludge is the difference in the top of the sludge and the firm resistance of the bottom (usually clay, liner, or concrete). A GPS or transect system can help you calculate the quantity of sludge in a lagoon.
Dredging is the method to remove sludge from a lagoon. If the lagoon can be taken offline and drained, then excavating the sludge may be an option. Otherwise, a hydraulic dredge can pump sludge from the bottom of a lagoon to remove it and restore the lagoon’s original depth.
The time really depends on the amount of incoming sludge and capacity. However, most lagoons require dredging every 5 to 10 years on average. Some lagoons that treat or capture organic matter can be aerated and treated to extend the timeframe. Sludge depth can be monitored to provide data for timelines and planning of the next dredge.
The most common method to dredge a lagoon is an auger dredge. Auger dredges are typically cable driven that are anchored along the shoreline. The auger is usually 6 to 8 feet wide and turns to move sludge toward the center where the suction intake from the pump is located. Sludge is pumped via a pipeline to be dewatered in drying beds, belt presses, settling ponds, geosynthetic tubes, filter presses, or other dewatering means. The auger can be set to a specific depth or guided with wheels or guides to prevent damage to liners within lagoons.
