ABSTRACT Nondestructive methods were investigated to effectively discriminate disposal-restricted materials, including aluminum, batteries, combustibles, lead, and mercury, inside waste containers without opening them. An industrial computed tomography (CT) system with maximum X-ray energy of 9 MeV was used to visualize inside 27-cm diameter pails and 59-cm diameter drums filled with typical waste materials such as combustibles, glass, concrete, and metals. The CT images with 0.5 mm spacing in the height direction were acquired and three-dimensional (3D) models were constracted from the serial tomographic datasets. Generally, a good linear relationship was observed between the gray values in the obtained CT images and the densities of materials. Combustibles, lead, and mercury were extracted from the CT images using simple segmentation by selecting specific gray-value ranges and binarizing the image, due to their lower or higher apparent densities compared to other materials. 3D feature-based discriminations were further applied to batteries and certain aluminum objects based on their structural characteristics. About 97% of the batteries contained in the drums were successfully discriminated regardless of deformation. Almost all of the missing batteries were under strong metal artifacts caused by large lead. Aluminum was extracted with a portion of glass and concrete, while very thin aluminum could not be detected due to its low apparent density. The discrimination methods developed in this study will be effective in revealing the contents of waste containers, particularly for harmful materials that need to be separated for proper disposal.
Read full abstract