1. Field of the Invention
This invention relates to a method and apparatus for homogenizing and sampling heterogeneous feedstock. More particularly, this invention relates to a method for providing a representative sample from heterogeneous feedstock containing solids, liquids, and volatile compounds that vaporize under standard atmospheric conditions.
2. Description of Related Art
Hazardous and/or radioactive materials are typically present in two forms, primary sources of contamination and secondary hazardous waste. Examples of primary sources of contamination are radioactive, chemical or biological materials. Primary sources of contamination by their nature present an increased risk to human health and the environment upon exposure and must be maintained and stored in such a manner as to prevent contact with both.
The handling of primary sources of contamination results in the generation of secondary wastes. Typically, secondary waste is a heterogeneous mixture of materials, such as protective clothing, polyethylene air canisters, handling equipment, sample bags, and laboratory sampling accessories (e.g., laboratory wipes, glassware, and swabs). Protective clothing may be in the form of full body suits, goggles, face masks, boots, and gloves. This secondary heterogeneous waste may be made from materials such as paper, cloth, vinyl, rubberized material, Tyvek(copyright), or metal. This secondary heterogeneous waste may be contaminated with organic compounds in the form of solvents, oils, liquids or in combination with each other and/or inorganic compounds or elements. The proper storage, treatment and disposal of the secondary heterogeneous waste depend on the type of contamination.
Typically, secondary heterogeneous waste is retained after use in appropriate containment vessels until a sufficient quantity of material is collected for disposal. Under parts 261 and 268 of the Resource Conservation and Recovery Act (RCRA), prior to final treatment or disposal, the secondary heterogeneous waste must be characterized to determine the proper treatment and disposal regime. The current procedure for obtaining samples involves personnel dressed in appropriate personal protective equipment opening the containers, reaching into the secondary heterogeneous waste matrix with a knife or scissors, cutting randomly-selected pieces of soft waste materials at different levels within the container, depositing them into sample jars, labeling them and sending them for appropriate analysis in accordance with Environmental Protection Agency (EPA) Publication SW-846. Due to the variability of the material that is contained in each vessel it may be difficult to generate a statistically representative sample of a small enough size, for later chemical and physical analysis. Normally, with this sampling method, items within each vessel may be missed, thereby providing inaccurate information for storage, treatment or disposal compliance purposes. Further, this method also exposes the sample taker unnecessarily to radiation and/or chemical hazards.
Another problem associated with sampling the secondary heterogeneous waste is how to accurately capture volatile organic compounds at the detection limits required under the regulations. Oftentimes, hazardous chemical constituents adsorbed onto, or absorbed into the soft waste matrices are not properly detected in the samples. This may be due to matrix effects, sampling error, the inherent inaccuracy of the current sampling method, or a combination of any or all of these.
An object of this invention is to provide a representative sample from heterogenous feedstock.
Another object of this invention is to provide a process that will retain volatile organic compounds contained within a feedstock during the sampling procedure.
Another object of this invention is to provide a process that is consistent with the hazardous waste regulations.
Another object of this invention is to provide a process that reduces the number of samples required to adequately characterize a population of heterogeneous waste.
Another object of this invention is to provide a contained apparatus such that the apparatus is maintained at cryogenic operating conditions and minimize the spread of radioactive and/or hazardous material and personnel exposure.
These and other objectives of the invention, which will become apparent from the following description, have been achieved by a novel apparatus and process for providing a homogeneous analytical sample comprising: providing a heterogenous feedstock having an average initial particle size; reducing the temperature of the heterogeneous feedstock to a temperature below a critical temperature; conveying the heterogeneous feedstock (rubber, latex, plastic, paper or wood) to a size reduction device; reducing the size of the feedstock components; blending the reduced size feedstock to form a homogeneous mixture; obtaining a representative sample of the homogeneous mixture. Critical temperature is used herein to mean a temperature below which a significant portion of the feedstock is embrittled such that it will break or fracture upon bending, as opposed to flexing, as well as retain the volatile organic compounds. Preferably, the critical temperature is less than about 100 K (xe2x88x92173xc2x0 C.). Herein, heterogeneous feedstock refers to a mixture of materials having a wide variability in size (e.g., supplied air suits which are 6 feetxc3x972 ft to paper tissue which is 1 inxc3x972 inches) and chemical compositions. The heterogeneous feedstock further comprises rigid solids, flexible solids, liquids, and volatile organic compounds. The volatile organic compounds may include, but are not limited to, methyl ethyl ketone (MEK), carbon tetrachloride, benzene, toluene and vinyl chloride. Preferably, the process of this invention maintains the representative sample below the critical temperature prior to being analyzed. Preferably, the size reduction and blending step are maintained at or below the critical temperature. Preferably, the process of this invention maintains the representative sample below 100 K (xe2x88x92173xc2x0 C.) and more preferably 77 K (xe2x88x92196xc2x0 C.) prior to being analyzed. The process is such that volatile organic compounds present in the feedstock are retained in the representative sample. Preferably liquid nitrogen is used to reduce the temperature of the feedstock below the critical temperature and maintain the temperature below the critical temperature.