The study, published in the journal Waste Management, determines that the estimated production of compost by 2025 could supply 21% of the nutrient needs of urban and peri-urban crops in the Metropolitan Area of Barcelona (AMB), further reducing environmental impacts.
This would require "an increase in the selective collection of organic matter and compost production capacity according to the metropolitan waste management program (PREMET25)", says Juan David Arosemena, ICTA-UAB researcher and lead author of the study, who stresses that there is a great opportunity to further optimize the circularity of nutrients in cities and thus take advantage of all its benefits.
The 5,568 hectares of peri-urban and urban agriculture in the Metropolitan Area of Barcelona require a total of 1,474 tons of NPK nutrients (nitrogen, phosphorus and potassium) yearly, three essential elements for plant growth. Of these, nitrogen is the most demanded with 769 tons, followed by potassium, with 592 tons, and phosphorus, with 113 tons. Most of the nutrients needed are used by cereals (42%), vegetables (38%), sweet fruits (11%) and legumes (5%).
From the 5,106 tons of compost produced from the AMB's organic solid waste yearly, 113 tons of NPK nutrients (phosphorus 44 tons, potassium 37 tons, and nitrogen 32 tons) could be recovered, in addition to other elements.
Apart from nourishing crop fields, compost production has important environmental benefits for cities, such as reducing methane emissions from mixed waste treatment in landfills, using biogas as an energy source, and replacing industrial mineral fertilizers in agriculture. These industrial mineral fertilizers are not only made from finite resources (as in the case of phosphorus), but also require a lot of energy and fossil fuels to produce (as in the case of nitrogen).
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