Recycling Wood Products via QXR-W - Maximizing the Reusable Fraction and Minimizing the Quantity of Hazardous Waste

Papers delivered at 2005 COST E31 Conference on Management of Recovered Wood, outline regional rules and regulations regarding acceptable levels of contaminants of recyclable wood for use in wood based panels and particle board. These vary depending on the governing body, but for the most part are within a general range of agreement per contaminant.   

Testing for these contaminants are generally the same, that is, random, manual sampling performed per lot (truckload). Samples are mixed via grinding and further sampled for analysis via common laboratory techniques (AA, ICP, IR, etc.)

The above listed allowable limits of detection for each of the contaminants is set for blended samples not individual pieces. The assumption is that manually extracted samples would be adequate representation of the whole lot of incoming material. That is to say, when the entire load is prepared for use in the new product the extracted sample is hopefully indicative of what the values of each of the contaminants will be in any prepared product.

There are several concerns with this analytical approach and the limits set forth. First, unless the whole lot of wood supplied for recycling is homogeneous, then there will be sampling errors. What these errors are is highly speculative and significantly dependent on the sampler itself. But it is not unreasonable to consider that sampling errors alone may contribute in the range of 100-1000 percent error. Therefore sampling errors may make acceptable incoming material appear to be bad or worse, it may indicate that unacceptably high contaminated material is good for use.

Second, the nature of contaminated wood (such as pressure treated wood) is that is it is present in large concentrations. A piece of 0.25 lb/ft 3 CCA rated pressure treated wood contains nearly 1% by weight of that chemical. Again, when a piece of incoming material is contaminated, it is highly contaminated when viewed against the above limits. It is extremely important to note that a single piece of contaminated material can adversely affect the value of an entire lot of incoming material.

Third, as can be seen from the above table, typical virgin wood values averaged over many types and times can be at, or near, the set limit for blended incoming material for recycling. Some maximum values reported were as high as 400 ppm Cu, 340 ppm Pb and 1.2% Cl! This can only mean that some virgin wood is also unacceptable per the limits established by some governing bodies. So these must be considered contaminants as well.

Therefore, the opinion held here is that there is only one way to truly guarantee that only acceptable product is manufactured and that is to make sure that only acceptable incoming product is used in the manufacturing process.

The Austin AI QXR-W is the only technology currently available that is economically feasible to ensure all incoming material is screened to ensure acceptable finished product. This is achieved by rapidly and automatically screening ALL incoming material, one piece at a time, with powerful analytical XRF technology, engineered to perform very fast analyses with low levels of detection of all the elements listed as contaminants.

The QXR-W, material and situationally dependent, can produce 3-5 tons per hour of screened incoming product, automatically and accurately. This is possible due to the following facts:

1. Incoming material, when contaminated via human intervention such as preservatives, coatings, and other treatments, yields a level that is many times above the limits imposed for recycling. For example, referring to the CCA example previously mentioned, 0.25 rated material contains about 8000 ppm of the CCA chemical. Gravimetric factor corrections yield approximate metal equivalent values of 1600 ppm Cr, 1100 ppm Cu, and 1400 ppm As. This value is several orders of magnitude above the allowable limits and more importantly, above the high values found naturally in some virgin wood.
2. The QXR-W can see a piece of 0.25 rated CCA pressure treated wood in less than 100 milliseconds. So material moving along a conveyor belt or slide-way device at rapid speeds (100 feet/minute) still has sufficient residence time in the analytical zone to be recognized and rejected.
3. Most contaminants listed can be seen even when the piece is wet, or dirty, stained, or even painted. Cl, and to some extent Cr, are susceptible to some degradation of performance under these conditions.
4. XRF is listed as an approved method by most regulating agencies for determining metal contaminants in recyclable and recoverable wood. And unlike other techniques, XRF can be set for screening all these elements of interest at one time.

In summary, the QXR-W is a viable tool for minimizing the amount of hazardous waste (contaminated wood) and coincidentally maximizing the amount of legally recyclable material--a true liability/asset management tool. Return on investment analysis is dependent on many critical and changing parameters, but typical ROI results have been determined in the 6-12 month time frame.

EPF's (European Panel Federation), Germany 's Alholzverordnung, and those supplied by one the of the world's largest supplier of composite wood for furniture use.

For details, contact xrf@austinai.com, or - 512-837-9400