Decision modelling for environmental protection: The contingent valuation method applied to greenhouse waste management

Over 380 000 t of vegetable waste are produced annually in the “Campo de Dalías” zone (Almería, South-eastern Spain) from horticultural crops grown in greenhouses. Landfills containing this vegetable waste are a potential breeding ground for diseases and pests and a source of greenhouse gas (methane). Moreover, they may also cause uncontrolled burning, riverbed blockage, poisoning of animals and produce an undesirable visual impact on the landscape. The only way to prevent or minimize this problem is to adopt a comprehensive and environmentally sensitive waste management programme. Using the contingent valuation method (CVM), it has been verified that farmers might be willing to pay more than they do at present for waste management if the residue was to be re-utilized, and two different uses have been evaluated: (1) a composting plant and (2) an energy-recycling process to desalinate sea water for irrigation purposes. The methodology has allowed a monetary value to be ascribed to the total environmental benefit. In addition, a Geographical Information System (GIS) has been used to locate an optimal area for a composting plant. The solution obtained takes into account all the environmental restrictions considered and, at the same time, it minimizes the transportation cost of organic waste from the production areas to the treatment facility. The subsequent integration of the results in a generalized cost–benefit analysis suggests the composting project as the best alternative when the environmental benefit of recycling vegetable waste was economically internalized.