Abstract
PurposeNew environmental strategies are emerging for cities to become more self-sufficient, such as hydroponic crop production. The implementation of such systems requires materials that usually originate in countries with low labour costs and other legal regulations. To what extent could these strategies be shifting problems across the globe? To answer this question, we performed a comprehensive environmental and social assessment of the various extended soilless systems used to grow vegetables on urban roofs.MethodsThree different growing media constituents were chosen for this study: perlite, peat and coir; which are produced in three countries, Turkey, Germany and the Philippines, respectively, and are imported to Spain. By using a life cycle assessment, we evaluated the environmental performances of the production and transport of these growing media. Additionally, we performed a social life cycle assessment at different levels. First, we used the Social Hotspots Database to analyse the constituents in aggregated sectors. Second, we performed a social assessment at the country and sector levels, and finally, we evaluated primary company data for the social assessment of the constituents through questionnaires given to businesses.Results and discussionThe coir-based growing medium exerted the lowest environmental burden in 5 out of 8 impact categories because it is a by-product from coconut trees. In contrast, perlite obtained the highest environmental impacts, with impacts 44 to 99.9% higher than those of peat and coir, except in the land use. Perlite is a material extracted from open-pit mines that requires high energy consumption and a long road trip. Regarding the social assessment, peat demonstrated the best performance on all the social assessment levels. In contrast, coir showed the worst scores in the Social Hotspots Database and for the impact categories of community infrastructure and human rights, whereas perlite displayed the lowest performance in health and safety. Nevertheless, coir and perlite evidenced much better scores than peat in the impact subcategory of the contribution to economic development.ConclusionsThis study contributes to a first comparison of three imported growing media constituents for urban rooftop farming from environmental and social perspectives to choose the most suitable option. Peat appears to be the best alternative from a social perspective. However, from an environmental standpoint, peat represents a growing medium whose availability is aiming to disappear in Germany to preserve peatlands. Therefore, we identify a new market niche for the development of local growing media for future rooftop farming in cities.
Highlights
Cities are primordial human settlements of prosperity in our society, generating approximately 80% of the global gross domestic product (GDP) (Floater et al 2014), and they provide economic and cultural wealth and dynamic territories
The growing media are mainly imported from other countries to Spain, which is the top producer of vegetables and fruits in the European Union (EU) (Messe Berlin 2020)
Coir only obtained significant impacts compared to perlite in marine eutrophication (ME) and water consumption (WC) because of its transport by sea, representing 56 and 42%, respectively, of the impacts of perlite
Summary
Cities are primordial human settlements of prosperity in our society, generating approximately 80% of the global gross domestic product (GDP) (Floater et al 2014), and they provide economic and cultural wealth and dynamic territories. The accumulation of populations, activities and resource demands triggers high pressures. Organisations, governments and academia have focused their attention on cities as high emitters and because they offer potentials for multipurpose and replicable solutions for sustainability actions (Grimm et al 2008; Rosenzweig et al 2010). Many strategies for redressing the ecological problems associated with urban areas have emerged over the years. These initiatives can be grouped into different topics, such as waste management, energy efficiency, water demand, buildings, and renewable energy (Lamb et al 2019). One initiative has stood out for its remarkable exploitation potential: the use of urban roofs for different purposes, as roofs can comprise up to 32% of the horizontal surface of build-up areas and are mostly underutilised spaces (Frazer 2005). Roofs can be used for implementing energy production (Madessa 2015; Kyriaki et al 2017; Bazán et al 2018), green roofs (Fioretti et al 2010; El Bachawati et al 2016; Brudermann and Sangkakool 2017), rooftop farming (Montero et al 2017; Nadal et al 2017, 2018a, b), the harvesting of rainwater (Farreny et al 2011; Angrill et al 2012, 2016) or a combination of these applications (Benis et al 2018; Corcelli et al 2019; Toboso-Chavero et al 2019, 2021)
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