# Constructed Technosols: A Strategy toward a Circular Economy
## 4 Waste Materials in Technosols Design
### Growing Material from Wastes
C&DW: Construction and demolition wastes. waste. Moreover, in the compost N and P were associated to stable organic matter and not easily available, representing a long-term reserve, whereas in the green waste these nutrients were associated with labile organic matter and thus releasable easily. The quantification and qualification of the fungal biomass may be also taken into account when organic wastes are selected as active biomass. Fungal flora, especially, is often correlated with the formation of stable aggregates [106; 107]. However, the fungal biomass present in organic matter could lead to problems of water repellence in the constructed technosol. [PERSON] et al. demonstrated that, although biochar and hydrochar are suitable to improve available water capacity in sandy soils with a decrease of bulk density, in case of hydrochar an enhanced hydrophobicity was observed due to fungal colonization [108]. On the other hand, to identify the most suitable materials and mixtures for Technosols made for specific purposes, it is also important to consider the plant species chosen for the site, as each species has different growing needs. [PERSON] et al. [93] studied different plant species on a constructed soil obtained from construction and demolition wastes, a topsoil, bentonite, and bio-stabilized compost. For grass and legumes, as well as for crop rotation cultures (rape, wheat, sunflower), they observed that high compost percentages support biomass growth. Conversely, forestry species (trees, bushes, shrubs) and willlow trees showed lower survival rates in the mixtures with greater compost percentages. Similar results were obtained by [PERSON] et al. [109]. They tested mixtures of excavated subsoil, crushed concrete, and green waste compost to identify the most suitable composition for tree growth, assess soil fertility by macrofaunal colonization and determine also the most tolerant tree species. The investigated constructed soils were [109]: excavated subsoil, excavated subsoil and concrete (30:70 \(v/v\)), excavated subsoil and compost (90:10), excavated subsoil with both concrete and compost (20:70:10 \(v/v/v\)). The tree species _Acer campestre, Acer platanoides_, _Acer pseudoplatanus_, _Carpinus betulus_, _Prunus avium_, _Tilia cordata_ were chosen for the study. Although the total annual tree mortality rate was higher than in other studies, due probably to the planting method, the best substrate resulted the mix of subsoil, concrete, and compost with a plant survival percentage of 89% and a good tree growth. The best adapted species were _Acer campestre_ and _Prunus avium_ that showed a survival percentage of 100%, whereas _Carpinus betulus_ was not well adapted, with a high mortality [109]. Another advantage brought by the organic matter addition is the possibility of pollutants removal. In fact the organic fraction could have effects on the bioavailability of contaminants, as it is able to adsorb or biodegrade organic pollutants by indigenous microorganisms [100]. A study by [PERSON] et al. compared the loss of phenanthrene in natural and artificial soils, made from 70% quartz sand, 20% kaolin clay, and 10% Sphagnum peat. After 84 days from exposure to phenanthrene, they observed a reduction both of pollutant content in soil and of the uptake by worm (_Enchytraus albidus_) in artificial soils. This behavior can be justified by the presence of microRNA in the peat able to mineralize and reduce the bioavailability of PHAs.