The fully dewatered media is ready for shipment to a disposal facility.
Click here to enlarge imageWater quality greatly affects the adsorption media’s arsenic removal capacity. The operating cycle starts out with very low and often non-detectable effluent arsenic concentration. As the volume treated grows, the effluent arsenic concentration gradually increases to the point where adsorption capacity is met. Capacity is usually reached after several months, but it can sometimes take several years. Once exhausted, the media is removed from the treatment vessel and replaced with new media. Exhausted media is tested and then disposed of at an approved landfill.
Regardless of the removal method, testing for acceptance at the landfill must be carried out prior to disposal. The Toxicity Characteristic Leaching Procedure (TCLP) test is a common requirement for most landfills. However, disposal location options should be reviewed to determine which, if any, other tests need to be conducted prior to the media being disposed.
Removal/Replacement Options
Direct vessel discharge and vacuum/slurry removal are the two most common methods for removing exhausted media from the treatment vessels. Media installation is accomplished by bulk placement or slurry transfer. Media handling considerations are important in the plant design phase since this affects vessel and plant construction details.
With direct vessel discharge, a media discharge connection must be located on the vessel side at the media and support gravel interface. A full throat valve is located at the connection to prevent media loss during operation. A discharge pipe connects the valve to a discharge pit where the exhausted media is sent. To remove the media, the vessel influent and effluent valves are closed and the media discharge valve is opened. Water and media contained in the vessel flow out the discharge pipe. A slow backwash is conducted to remove all media from the vessel. An access hatch on top of the vessel allows operators to confirm when all media is removed. Once in the discharge pit, water is allowed to drain out of the media to minimize weight hauled to the landfill. Two advantages to this method include minimal vessel unloading time and minimized direct media handling.