**5. Separate collection systems for biowaste**

An average of 520 kg of urban waste was generated *per capita* in the European Union in 2005 (Blumenthal, 2011) and this figure is expected to rise to 562 kg by 2020 (EU, 2011). If we consider this prediction to be correct, 290 million tons will be generated in 2020, of which 36% will be organic waste, and as such the amount would rise to 104.4 million tons. This is a very significant amount, and as such one would expect that the technology and the number of facilities for the use of this material would be greatly enhanced.

The organic fraction of urban waste consists of biodegradable materials (food scraps, spoiled food, gardening waste, etc.). European Union legislation, in the Framework Directive on Waste (Directive 2008/98/EC) defines "biowaste" as "biodegradable garden and park waste, food and kitchen waste from households, restaurants, caterers and retail premises and comparable waste from food processing plants", meaning that the organic fraction can be classified as biowaste, like wood, sewage sludge, and agricultural and forestry waste. This is very important from a legal standpoint, since this Directive requires EU member countries to implement separate collection and recovery, thereby reducing greenhouse gas emissions, the recovery of biowaste as biogas and compost, and a reduction in the amount of waste dumped at landfill sites.

The main objective of the separate collection of the organic fraction of urban waste is to convert it into high quality compost. This material can be used as fertilizer for agriculture, gardening or landscape restoration work. The critical factor is the percentage of improper materials accompanying the organic fraction of urban waste. It is therefore essential that this operation is carried out under the best possible conditions.

The greatest difficulty in establishing a separate collection system is designing the precollection, to make it as convenient as possible for citizens and not unduly expensive for the Council. Two aspects depend on public participation: the amount of waste collected and its quality. The former justifies the system's existence and the latter prevents composting centres from receiving waste that is more similar to the mixed waste fraction than the organic fraction, as occurs in some cases. Another important external factor that can affect the system is the existence of a potential market which guarantees the destination of the compost in the territory of the composting plant. If this market does not exist, alternatives such as biomethanation or incineration after drying can be considered. In order to minimize the energy costs of drying, biological drying systems (biodrying), solar drying or a combination of both can be used (Adani *et al*., 2002, Velis *et al*., 2009, Zhang *et al*., 2009).

Separate Collection Systems for Urban Waste (UW) 127

considerable time and effort. To that end, a representative sample of that population (279 towns) was defined according to a number of statistical variables. Each one was sent a

General information about the municipality: number of inhabitants, area and collection

 For each of the waste fractions collected separately: tonnes collected annually; composition; the year separate collection was implemented; the number of containers

After the entire information gathering process, data was available for 115 towns (41% of the

Of all the towns for which information was available, 29.5% collect the organic fraction of urban waste, the majority are in the region of Catalonia, as the legislation there requires this type of collection. Such a low percentage is due to the fact that collection of the organic fraction of urban waste is still voluntary, and as such the majority of the towns have not yet implemented it. According to the study, there are 6 different collection systems, with the

 SYSTEM A: separation into 4 fractions (mixed waste, organic waste, paper-cardboard and glass). Mixed waste and biowaste is collected at kerbside, while paper-cardboard

 SYSTEM B: separation into 5 fractions (mixed waste, organic waste, paper-cardboard, glass and lightweight packaging). Mixed waste and biowaste is collected at kerbside, while paper-cardboard, glass and lightweight packaging are collected at drop-off points. SYSTEM C: separation into 5 fractions (mixed waste, organic waste, paper-cardboard, glass and lightweight packaging). Mixed waste and biowaste is collected at kerbside, while paper-cardboard, glass and lightweight packaging are collected at drop-off points. The collection of biowaste is partially implemented and collected door to door.

 SYSTEM D: separation in 4 fractions (mixed waste, organic material, glass and multiproduct1). Mixed waste and biowaste are collected at kerbside, while multi-product and

 SYSTEM E: separation in 4 fractions (mixed waste, organic material, glass and multiproduct). Mixed waste, biowaste and multi-product are collected door to door, while

SYSTEM F: separation into 5 fractions (mixed waste, organic waste, paper-cardboard,

The diagram of the 6 collection systems can be seen in Figure 6. Table 2 shows the towns

Table 2 shows how system B is used in most of the municipalities studied. There is a new fraction, multiproduct, in systems E and F, in order to optimize collection. This fraction is not very widespread, and is not found in large Spanish towns (Gallardo et al., 2010). Figures 7-12 shows the different *FRo* obtained by each system and Table 3 shows the *QCRo* and *SRo*

glass and lightweight packaging). All fractions are collected at the kerbside.

glass is collected at drop-off points. This is a variation on System D.

survey by mail, requesting the following information:

towns in the sample), in 14 of the 17 Spanish regions.

and glass are collected at drop-off points.

This is a variation on System 4.

glass are collected at drop-off points.

that have implemented each of the systems above.

1 Multi-product: light packaging and paper-cardboard

system in place.

following characteristics:

for organic waste.

and frequency of collection.

The systems that can be applied to the collection of the organic fraction of urban waste are the same as those mentioned above. As described above, special attention must be paid to the pre-collection, which consists of separation in an organic waste bin, preferably in compostable bags, such as those made of corn starch. The bags are then deposited in special containers for transport to composting plants. In order to minimize the amount of improper materials appearing in the containers, initial campaigns and information maintenance initiatives are carried out, and biodegradable bags are often given away. It is also quite useful to conduct a pilot test in one part of the city, in order to gain experience and roll out the service to the rest of the city.

In order to increase the amount collected and reach more generation points, the collection of material can also be arranged according to its origin (Marrero, 2010):


After a separate collection system for the organic fraction of urban waste that meets the needs of the population concerned has been established, its main advantages are:

