**1. Introduction**

Separate collection of urban waste can be defined as a specific collection system that allows recoverable materials in waste to be separated. The human factor is very important in this new collection model, as the citizen now plays an active rather than a passive role as a processor of materials at source.

Various solutions for separate collection have emerged in order to fulfil all the objectives stipulated by legislation and local authorities in various countries for the recovery of municipal waste. Germany uses the Dual System, in which packaging waste is collected separately by a network belonging to companies selling consumer products. Separation of the organic fraction is mandatory in the Netherlands. In France and Spain, the governments are the responsible for designing mechanisms to implement the separate collection of packaging waste and achievement of the goals stipulated by European legislation. In the USA and Canada in the early 1990s, many cities with residential areas containing singlefamily homes began pilot schemes for separate collection, with waste separated at source into two, three and four fractions.

The large number of factors involved in establishing a separate collection system (economic, social, environmental, legal, etc.) means that there is no single solution or alternative. This has given rise to studies of citizens' behaviour with regard to the various collection systems: the level of participation, quality of the waste collected, financial incentives, etc. (White *et al*., 1995; Wang *et al*., 1997, Gallardo, 2000, Martin *et al*., 2006, Shaw *et al*., 2006, Dahlén *et al*. 2007). Other authors have analysed the various demographic, logistic and economic factors influencing citizens' participation, and assessed the quantities collected, generation and composition data for certain indicators based on these factors (Daskalopoulos *et al*. 1998, Emery *et al*., 2003, González-Torre & Adenso-Díaz, 2005).

Separate collection of organic waste has been implemented in countries in northern Europe for several years, and is now relatively well established there. It is not yet widespread in Spain or others countries in southern Europe, but there are experiences in many autonomous regions at local or regional level which have had varying degrees of implementation and success. The Framework Directive on Waste (Directive 2008/98/EC) introduced the concept of biowaste and the need to recover this type of waste. The organic fraction of urban waste is considered biowaste, and it accounts for 36% (UE, 2011) of urban

Separate Collection Systems for Urban Waste (UW) 117

studied as a separate subsystem consisting of the pre-collection and collection stages (Figure 1). When studied separately, it can be considered an independent system, in which the input consists of a stream of urban waste and the output is several streams of selected materials, which go to the next management stage where it is subjected to different recovery methods. Separate collection is influenced by a number of environmental factors that influence the

Pre-collection includes handling, processing and storage of urban waste by citizens before it is deposited at the collection points, where there are different types of containers (Figure 2). After it has been deposited and stored at these points, the waste is collected and transported to the next facility in the urban waste management system. Most recovery methods, such as recycling or incineration, require separation into different fractions at source in order to achieve the minimum quality levels required in these processes. To that end, there is a wide range of fractioning at source, which can range from level zero, i.e. unfractioned or "all in

one" collection, to a high level of specific separation of materials (Table 1).

Fig. 2. Urban waste collection containers in Spain.

choice of the alternatives in the two elements of the system.

Fig. 1. Separate collection diagram.

waste. As such, its separate collection is expected to be enhanced in all European Union countries, in order to use it and minimize its deposit into landfill.
