Background The production of waste is one of the most important concerns for our society. The generation of water treatment plant mud is growing considerably in Andalusia with the completion of the water treatment plant network. Currently 105,000 tonnes of dry material/year are produced but the figures can be expected to rise substantially over the next few years. As for solid urban waste, production was 2 million tonnes per year until recently; now the figure stands at 3 million tonnes/year and continues to increase. It is very difficult to reduce urban solid waste, especially the organic part, making treatment in a manner that converts it into a useable sub-product advisable. As for plant waste, although this is comparatively a less serious problem, it also needs to be dealt with. Making compost offers a very interesting possibility in this respect. In accordance with European directives, Spain has developed national and territorial management plans to deal with the problem of waste, with the production of compost considered as the main alternative. Decree 218/1999 issued by the Andalusia Regional Government is a demonstration of the interest that exists for recovering the maximum proportion of organic waste for use as soil correctives, for the construction of plants for recovering and manufacturing organic fertilisers and for the use of compost, with preference for restoring damaged soils. Specifically, the application of composts can be considered to be an efficient remedy against erosion, desertification and the loss of soil fertility. Another notable aspect for a community that depends largely on agriculture is the contamination of surface and underground water by nitrates of agricultural origin. The gradual implementation of compost in the agricultural market will be a step towards eradication of this problem. Objectives The project's objective was to demonstrate that organic waste from human activity, such as household rubbish, bio-solids from urban waste water treatment plants and plant remains from parks and gardens, could be a valid resource from the technical, economic and environmental points of view for co-composting or joint composting. In the first phase compost would be processed in two composting plants that initially did not carry out co-composting. In the second phase the compost obtained would be tested as humus in gardening, landscaping and forestation, like an organic fertiliser in forest and agricultural cultivation, and as substratum in forest, ornamental and horticultural greenhouses. In the third and last phase the results would be widely disseminated, concentrating efforts in the project area, and a 'LIFE Compost Office' would be created in Andalusia as a permanent two way feed-back point and permanent source of information about co-composting technology and the application of compost. Also to be promoted was a 'LIFE Compost Forum' in which the technical, economic and environmental aspects could be debated. Results The aim of this project was to demonstrate that organic waste from human activity, bio-solids from urban waste water treatment plants and plant remains from parks and gardens were valid resources for co-composting or joint composting, from the technical, economical and environmental points of view. It was planned that three types of compost would be produced, in the following quantities: Type compost/Bio solids fr. waste wat treat plants/Urban waste/Plant biomass/Product.(Tn) A 1 0 3 500 B 0 1 1.5 350 C 1 1 2 50 75 plots with different species were established to check the compost application. Results were obtained for all of them. The test groups were broken down into: - Nurseries: ornamental, forest and vegetable - Crops: silvicultural and agricultural - Reforestation and landscaping In general, proportions with 40 to 50 percent of compost A or C demonstrated that good quality urban compost was a favourable substitute for peat, topsoil, manure and organic amendments. Summarised results were as follows: - Reforestation: compost stimulates growth when added to the planting hole in reforestation projects - Landscaping: compost accelerates the establishment of lawn if incorporated into the surface before it is planted. - Silvicultural crops: it increases wood yield by more than 50 percent when applied to trees in forest plantations - Agricultural crops: when used as basic fertiliser in irrigated agricultural crops the crop yield increases. In some crops it improves the quality of the fruit (watermelon). - Ornamental nurseries: the three types of compost gave very good results, especially compost A. For certain species (Citrus aurantium, Cupressus sempervivens and Ceratonia siliqua) the stay in the nursery could be reduced by one year. - Forest nurseries: The type A and C composts achieved very good results with species in clayish soils, whereas type B composts were appropriate for sandy soils. When mixed with peat in nurseries compost favours plant development and keeps the plant in good botanical condition for a longer period of time. - Vegetable nurseries: the compost increased growth rates and reduced growing times in the nursery The technical specifications and the test reports are available on the web site. This project has been selected as one of the 24 "Best" LIFE Environment projects in 2004-2005