Abstract
Construction of Technosols offers interesting alternatives to two current problems in the city of Vitoria-Gasteiz (Spain): waste recycling and degraded plot recovery. To evaluate the viability of their use, 6 types of Technosols were created by mixing four different byproducts from municipal waste treatment plants. The less than 40 mm size fraction material from the municipal construction and demolition waste treatment plant was used as the main ingredient, bio-stabilized material from the solid urban waste treatment plant mixed with triturated pruning was used as organic matter input, recycled bentonites and topsoil from the public plots of Vitoria-Gasteiz (Spain) completed the mixture. Mixes were prepared in triplicate and installed in 48 m<sup>2</sup> cells along with another 4 control cells containing only one of the ingredients at the municipal landfill of Gardelegui. A monitoring program for different parameters on soil, eluates and natural leachates was established to test the Technosols’ capacity to sustain vegetation without negative impacts on the environment. The final objective is to test their ability to restore unused municipal plots. Results from the first year show that Technosols are a suitable option for degraded sites restoration and green infrastructure support. All controlled parameters on soil are within the limits set by autonomic legislation for land use as public park. The eluate analysis concludes for all studied parameters that all mixes would be classified by legislation as inert waste, except for the sulphate concentration (which exceeds the inert waste limit of 1 000 ppm), that currently would label the soil as non-hazardous. In the natural leachate analysis strongly basic pH values were present above 9.5, the limit allowed in Royal Decreet 849/1986, but acidified throughout the year moving towards neutrality, with final values between 7.31 and 7.51. Leachate from CDW30, TS15 and RB30 Technosols showed not allowed values with respect to sulfates and Fe during the last sampling, surpassing the limits of 2 mg/l and 2000 mg/l respectively. All studied Technosols presented a low ecological potential risk (RI &lt; 150) for heavy metals in soil and eluates.
Highlights
The presence of soils with high risk of degradation produced by humans has been a problem in the last years in several zones, for example, a tentative assessment for the soil degradation status in South America revealed that about 14% of the total land areas of South America was affected by human-induced soil degradation (Oldeman et al 1991)
One approach to urban soil remediation is the use of Technosols: soils whose characteristics and pedogenesis are dominated by their technical origin (IUSS Working Group WRB 2015)
Technosols were made by mixing the following materials: construction and demolition dirt composed of the less than 40 mm size fraction of the construction and demolition waste processed in the treatment plant of Gardélegui as the main ingredient; bio-stabilized material from the “Biocompost de Álava” plant of mechanicbiologic treatment of urban wastes mixed with crushed prunings from the public garden maintenance as organic matter source; recycled bentonite from the ECOFOND sand foundry in Salvatierra-Agurain as a clayey component; and topsoil from municipal plots (“Vitoria’s topsoils”) stored in the Municipal Vivarium
Summary
The presence of soils with high risk of degradation produced by humans has been a problem in the last years in several zones, for example, a tentative assessment for the soil degradation status in South America revealed that about 14% of the total land areas of South America was affected by human-induced soil degradation (Oldeman et al 1991). One approach to urban soil remediation is the use of Technosols: soils whose characteristics and pedogenesis are dominated by their technical origin (IUSS Working Group WRB 2015). These Technosols are based in the application of technology and scientific knowledge to create soil mixes depending on the characteristics of a particular problem (Ibarrola 2015). Technosols are part of the reference groups of the World Reference Base for Soil Resources (IUSS Working Group WRB 2015) and are considered as a mechanism against the greenhouse effect, being an interesting carbon sequestration alternative (Macías Vázquez 2004; Lorenz 2009)
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