Limitations of the TCLP fluid determination step for hazardous waste characterization of US municipal waste incineration ash

Abstract

The Toxicity Characteristic Leaching Procedure (TCLP) requires the use of one of two acid-based extraction fluids: fluid #1 or fluid #2, determined by the fluid determination step (FDS). Fluid #1 is a buffered solution of acetic acid and sodium hydroxide while fluid #2 is an unbuffered acetic acid solution. Motivated by divergent fluid determination results among different laboratories, the limitations of the FDS in the TCLP used for characterizing municipal solid waste incineration (MSWI) ash were investigated by varying three test parameters: solution cooling rate, degree of particle size reduction, and sub-sample selection. A faster cooling rate decreases the needed cooling time and has the potential to alter the fluid outcome to fluid #1. Excessive size reduction of particles forces all the fluid outcomes to fluid #2, possibly due to increased surface area and reaction rate of MSWI particles with the FDS media. Selecting larger particles increases the likelihood of obtaining fluid #1 while selecting smaller particles increases the possibility of requiring fluid #2, possibly due to the lower alkalinity of larger particles and higher alkalinity of smaller particles. These findings suggest that FDS can be conducted using different allowable approaches, based on the interpretation of the users who have the potential to alter the fluid outcomes to achieve a favorable extraction fluid. These limitations may allow MSWI ash to consistently "pass" the TCLP. These phenomena highlight a major flaw in the existing hazardous waste testing protocols for MSWI ash.

Keywords: Ash; Hazardous waste; Incineration; TCLP; Toxicity characteristic; pH.