According to the manner of collection, municipal waste is subdivided into unseparated municipal, separated dry and separated wet (organic and green) waste. In the Herambiente system, municipal waste collected separately by the environmental hygiene services is delivered to the separation or selection recovery plants, while most unseparated waste is sent directly to waste-to-energy or "pre-treatment" plants for separation of the wet fraction and subsequent biostabilisation. The separation and/or selection plants are divided into two main categories: DRY FRACTION RECOVERY PLANTS and MECHANICAL-BIOLOGICAL SEPARATION PLANTS. The first type of plant receives material obtained through the separated collection of dry fractions (paper, glass, plastic, etc.), while the second receives unseparated municipal waste (from grey bins), which undergoes a process of separation and material recovery (dry for incineration or landfill, wet for biostabilisation). Organic waste obtained from separated wet collection (organic kitchen waste, catering refuse, green waste, etc.) is taken to anaerobic biodigestion and composting plants.
Residues from the selection and separation processes, which are not amenable to material recovery, are taken to waste-to-energy plants or to landfills for final disposal.
The actual quantity of material recovered from separated waste depends on the quality of the collection and thus, to a large extent, on the care taken by the citizen in the initial disposal. In order to maximise material recovery, the waste obtained from separated collection of dry fractions (e.g. plastic, glass, paper, cardboard, tins, wood, ferrous metals, mixed materials, etc.) is passed through a selection plant, where any materials extraneous to the type of collection are discarded (non-reusable fractions). Herambiente´s selection plants process the municipal waste obtained from separated collection of the multi-material and mono-material fractions and of non-hazardous special waste, i.e. waste deriving from artisanal and industrial production activities that can be assimilated to municipal waste. The incoming waste is checked to ensure the conformity of the materials, and then sorted by type. If necessary, it is treated to remove any impurities that may be present, and then packaged and stored for subsequent recovery of material.
The selection process, which is carried out automatically using state-of-the-art technologies such as optical readers, CHARACTERISES THE MATERIALS EITHER AS RECOVERABLE WASTE, in the specific sectors of the National Consortiums (CONAI), or as secondary raw materials, meaning products that can be sold and re-used in production plants.