Glass poses a major disposal problem in garbage separation system. Once glass is crushed it is essentially impossible to sort manually by color. Crushed glass also contaminates other recycled materials such as cartons and plastics, lowering their quality and market value. Although markets for recovered glass are stable for brown and clear glass, these markets specify very low contamination. The demand for green glass is low due to its infrequent use. Most MRFs manually sort glass with clear flint being negatively sorted. These MRFs often lose money on the processing of glass because the market value does not justify the collection, labor, transportation and disposal costs.
The MRF will utilize a MSS DAR system to sort glass by color. The glass feed will be pre-processed with a trommel and an air classifier to remove non-glass materials. Light spectrophotometry will be used to distinguish among the different colors of glass so that they can be identified and separated. Specifically, the detection system will be based on the transmission of visible light at certain wavelengths to distinguish between clear, brown and green glass. If a mixed waste stream is eventually processed at the MRF, a method to distinguish ceramics and other opaque materials will be necessary. The removal of ceramics is important since the glass market is extremely sensitive to ceramic contamination. It is important to maximize integrity retention of the glass to both reduce contamination of other materials and to aid the DAR system. The system will also allow mixed glass recycling in addition to recycling by individual color if a good market is eventually available to avoid the expensive disposal costs of the rejected mixed cullet.