Technosols made from urban and industrial wastes are a good option for the reclamation of abandoned city plots

Rapid urbanization followed by economic crisis frequently results in the presence of degraded abandoned urban plots inside or in the periphery of cities. Urban greening can be a low-cost solution for their reclamation but, inevitably, the necessary plants require an appropriate medium to grow and thrive. In this study, Technosols were explored as a suitable option to simultaneously face two common challenges of many cities, i.e., the reclamation of degraded abandoned city plots and the recycling of industrial and urban wastes. To this purpose, a mesocosm experiment was carried out to assess the suitability of six different Technosols (resulting from the combination of the following four ingredients: CDW: construction and demolition wastes; BIO: bio-stabilized material from a municipal composting plant; BENT: recycled bentonites from a local industry; TS: topsoil from vacant public plots) for the reclamation of abandoned city plots. The six Technosols were prepared in triplicate and then installed in 12 m(2) experimental cells. Control cells containing only one of the ingredients (i.e., four controls, one per ingredient) were also included in the experiment. In each cell, four different vegetation treatments were established in quadrants: meadow (a mixture of grasses and legumes), crop rotation (rape, wheat, sunflower), forest (mixture of trees, bushes and shrubs) and tree plantation (willows). For three years after the implementation of the abovementioned treatments, a wide set of parameters (mainly, of physicochemical nature) were monitored in Technosol, Technosol eluate and cell leachate samples, following the applicable legislation. Most of the parameters monitored along the experimental period complied with the limits established by the applicable legislation by the end of the experiment. Nonetheless, the concentration of sulphates in the Technosol eluates exceeded the so-called inert legal limit but remained under the non-hazardous legal limit. All plant treatments showed a satisfactory growth except for willow trees, most likely due to water limitations. A higher amount of organic matter in the Technosol favoured the growth of meadows and crop rotations. Technosols showed a high heterogeneity, a limitation that should be taken into account when applying them in the reclamation of abandoned city plots. However, it was concluded that Technosols from urban and industrial wastes are a suitable option that promotes urban waste valorization.