Solid wastes are always collected as mixtures of different materials. They gets crushed, classified and sorted in solid waste treatment plants. Among these processes the sorting is the determining step for recycling and reuse. Traditional sorting technologies like magnetic sorting and eddy current sorting are only able to process some special kinds of ingredients of waste mixture roughly, such as the separation of ferrous and nonferrous metals. Since there exist corresponding force fields between waste particles and separators. Some other properties of the solid particles such as the colours, shapes and texture features could also be considered as sorting criterions but there is no sufficient force field between these properties and separators. Indirect sorting process by using optical sensor and mechanical separating system was developed. By using this system the particle sizes and positions, colours and shapes of each waste particle are able to be determined and used as sorting criterion. The mechanical sorting device consists of a compressed air nozzle which is controlled by computer, the target particles which were recognized by sensor were blown out of the main waste stream. Feature recognition by using optical sensor yield good results.
