Recovery of glass contained in the heavy residual fraction of Portuguese mechanical Biological Treatment Plants

The aim of this work is the valorisation of the heavy residual fraction of Mechanical Biological Treatment (MBT) plants fed with mixed Municipal Solid Waste. This product contains a significant amount of glass. In the present work, it was found that the glass content in this product varies from plant to plant. Minimum and maximum values of 33 and 67% were determined. This material is not recycled today, being instead landfilled, because the contamination with other materials is so high that is not possible to process it by optical sorting, which is the end-of-line technology used in glass recycling. Nevertheless, it is possible to upgrade this product by removing a significant percentage of the stones, the main inert contaminant, with a simple and cheap process, RecGlass, which exploits the differences in the shape of glass particles and stones. This paper presents the results of a study carried out with samples of 5 Portuguese MBT plants of different characteristics. The fraction <5.6 mm, composed mainly by organic matter, was removed. The influence on the results of the main operational parameter, the belt inclination, and the samples' characteristics, composition and particle size were evaluated. In only one processing step, the samples with a glass content of 58-69% were upgraded. By removing 50-90% in weight of the stones, the concentrated product reached 63-97% in glass content.