Landfill Disposal Considerations for Arsenic Treatment Residuals

Throw away adsorption media such as granular iron media (GIM) have been introduced in recent years as a method of arsenic removal from drinking water. In this process, the arsenic is adsorbed onto the surface of the oxidized iron media. The media is used until arsenic breaks through in the column effluent, and the spent media is removed and replaced with fresh media. The spent media is dewatered and placed in a municipal landfill as non hazardous waste. All residuals must pass the Toxicity Characteristic Leaching Procedure (TCLP) test before disposal.

Another process for arsenic treatment involves coagulation with ferric chloride and subsequent filtration of arsenic laden iron flocs. Periodically, the filter is backwashed to remove the accumulated solids and the spent backwash must be discharged to a sewer or be processed on-site. Processing of iron sludge on-site involves thickening and dewatering prior to landfill disposal. These sludges are also placed in municipal landfills as they pass the TLCP test, however they generally fail the California Waste Extraction (Cal-WET) test.

Recent studies by Ela and Ghosh indicate that mixing exhausted iron media and chemical sludges from arsenic treatment processes with domestic wastes in municipal landfills results in unstable arsenic treatment residuals, and potential leaching of arsenic from the spent media.

This paper discusses dewatering of chemical sludges from enhanced coagulation arsenic treatment and innovative clarification processes, along with the landfill considerations when disposing of these residuals.

Also, an overview of prior studies on arsenic residuals is provided along with a summary of the spent media characteristics. The potential for desorption of arsenic treatment residuals is also discussed. The leaching of arsenic from the residuals placed in a landfill, as they relate to the TCLP and WET tests are discussed.

Current and alternate disposal practices are described, along with the associated cost impacts.