Recycled materials for urban gardens

Overview & Synopsis

The global expansion of urban agriculture practices and the scarcity of green surfaces drive increased demand for soil-less cultivation systems and substrates. Commercial substrates are primarily composed of peat, which is sourced from peatland soils that, when depleted, can become primary carbon emission sources. Phasing out peat will require alternative cultivation substrates, which, in the context of an urban circular economy, could derive from locally available waste. Nevertheless, the potential pollution of secondary raw materials should be carefully managed to ensure safe use for the public. Within this context, this thesis aimed at studying the pollution from substrate, to edible fruit and to leachates in experimental urban gardens, where locally sourced wastes were employed for alternative substrates formulation. The pollutants of interests where trace elements (TEs) and microplastics (MPs). Trace elements pathways were studied in two urban gardens based in Madrid (Spain) and Nantes (France), where substrate composed of urban byproducts, being respectively totally organic and a mixture of organic and inorganic residues, were tested for the cultivation of tomato plants, which were then studied in both edible and non-edible parts. Regarding MPs, an analytical method employing pyrolysis coupled to gas chromatography and mass spectrometry (pyro-GC-MS) was developed and then applied to polymer spiked substrates. In this way, polymer recovery in the organic-rich substrates and derived leachates could be tested in a controlled system, allowing to validate on-site the analytical method