A Geochemical and Agronomic Evaluation of Technosols Made from Construction and Demolition Fines Mixed with Green Waste Compost

Abstract

Construction and demolition fines (C&D-fines) and green waste compost (GWC) are two commonly generated urban waste materials that represent repositories of geochemical value. Here technosols were produced from volumetric mixtures of these materials ranging from 0–100% C&D-fines, with the remaining proportion comprised of GWC. Agronomic assessment was carried out by way of pot and rhizobox plant growth experiments with ryegrass, barley and pea to determine germination, plant mass and rooting behaviours. Geochemical and mineralogical evaluation was achieved by soil pore water solution measurements combined with X-ray powder diffraction analyses respectively, to characterise the technosols and their distinct deviations from a reference agricultural geogenic soil (soil). The results demonstrated that germination, growth and root mass/surface area of vegetation were up to 80-fold greater after 30-days in the technosol composed of equal volumes of the two materials (50% C&D-fines: 50% GWC) compared to the soil. High concentrations of Ca and Mg in pore waters (550–800 mg·L−1) were dominant features of the technosols, in contrast to the soil (<50 mg·L−1), resulting from gypsum and calcite enrichment of the C&D-fines. In contrast, the GWC represented a source of soluble K (450–1000·mg·L−1). Highly elevated Ca concentrations in extended leaching tests of the C&D-fines reflected ongoing gypsum dissolution, whereas soluble Mg and K were rapidly depleted from the GWC. In summary, short-term performance of the technosols as plant growth substrates was strong despite their geochemical and mineralogical distinction from soil. Gleaning additional geochemical value from combining urban wastes in this way is potentially suited to myriad scenarios where geogenic soils are contaminated, sealed or otherwise absent. Further assessment will now be needed to determine the geochemical longevity of the technosols before wider scale applications can be recommended.

Land recycling, food security and Technosols

“…Furthermore, Lal et al (2021) [28] consider future land uses for sustainability of cities and megacities and for contributing to the fulfillment of Sustainable Development Goals (SDGs), are those related to urban garden, permaculture, vertical gardening and Technosols. Many cities use urban waste compost for urban agriculture [28] , and consider viable incorporation of wastes as a substrate for plant species with agricultural utility [29,30] . Some constraints in the allocation of intended use are size of brownfields (areas between 1 and 20 hectares are suitable for green spaces) [22] , soil state (contamination, fertility, among others) [23,31] , and previous use mainly related to whether it has been sealed or not.…”

Environmental Risk from Organic Residues

“…However, an efficient supply of nutrients to the soil is increasingly necessary since soil nutrient imbalance is a global threat to food security and ecosystem sustainability [1]. To optimize soil nutrient cycles and solve functional problems, the Food and Agriculture Organization (FAO) of the United Nations (UN) [2] and other authors [3][4][5] propose adding organic residues or constructing technosols [6][7][8], in line with sustainable agriculture, circular economy strategy and Sustainable Development Goals (SDGs) [9][10][11]. At the same time, the European Green Deal (EGD) aims towards carbon neutrality until 2050, with midterm goals of at least 55% decrease in greenhouse gas emissions by 2030.…”

“…Characterization and monitoring of residue mixtures are important, as well as the soil to which they are applied, since there may be an enhancement or a reduction in adverse effects, as in the case of metal mobilization and leaching [8]. Therefore, this work analyzes Cu, Zn, Cd, Cr, Ni and Pb elemental composition concentration in organic residues and their solubility content that may pose a risk after soil application, as HM can cause great concern [33].…”

From waste to valuable resources: exploitation of mineral waste in civil and environmental application.

“…The management and disposal of these waste categories is an open problem, as most of the coarse fraction (> 2 mm) of both materials is potentially recycled in several civil, building and environmental applications, while the ne fraction (< 2 mm) is mostly likely destined to land ll (Coull et al 2021, Magnusson et al 2015.…”