Use of manures and organic wastes to improve soil quality and nutrient balances CHARACTERIZATION OF MUNICIPAL SOLID WASTE COMPOSTS PRODUCED IN SPAIN

Composting is clearly reported as one of the most effective technique to transform organic wastes into an interesting resource, useful to improve soil characteristics and playing a potential role in reducing greenhouse gases, due to its high content in stable organic matter (Favoino and Hogg, 2008). However, its agronomical properties are dependent on several factors, which pollutant contents becomes the most restrictive for its use. Organic wastes produced in Spain correspond mainly to farming wastes, municipal solid waste organic fraction, sewage sludge and organic wastes from agrifood industry. Organic fraction of municipal solid waste is commonly managed in Spain by biological treatments, generally composting, to fulfil the requirements set by the EU Landfill Directive (1999/31/EC) and, as a result, this compost becomes a possible product to be used in agriculture. In Spain, municipal solid waste is regulated by Law 10/1998 on waste, which obliges municipalities of more than 5000 inhabitants to collect waste separately, but without special mention of organic fraction. On the other hand, Catalonia (NE Spain) has a specific regulation for waste since 1993 (Law 6/93 regulating waste) focusing on waste generation with special concern on separate source collection of organic fraction. This law has been recently modified (Law 9/2008), forcing all municipalities to collect waste separately, including those of less than 5000 inhabitants. Thus, in Spain, it is possible to find (a) composting plants processing organic fraction from source sorted municipal solid waste (mainly in Catalonia), and (b) other facilities that treat organic fraction from municipal solid waste collected on mass, and recovered by mechanical separation at the beginning of the process. In order to avoid soil contamination by pollutants application from composted organic wastes, several Members States of the EU have adopted specific regulations to establish limitations for some of pollutant contents. Spain is one of these countries, and its legislation has been focused mainly on heavy metals. However, some other parameters are also important to be considered before an agronomic use of composted organic waste. Unfortunately, no requirements are set in the Spanish law to assess the quality of compost organic matter, and only a threshold value, requested as a minimum content, is stated for the total organic matter of the product. This Spanish law, RD 824/2005 concerning fertilizers products, also provides requirements for the following parameters: moisture content, C/N ratio, percentage of impurities and particle size (Table 1). In this paper, the fulfilment of the requirements states by RD 824/2005 are evaluated for composts obtained from several municipal solid waste composting facilities of Spain.