Assessment of the environmental sustainability of a treatment aimed at soil reuse in a Brownfield regeneration context
June 5-10, 2016
In the past decades the number and extent of Brownfields, i.e. abandoned or under-used sites that may present a contamination problem, has continued to grow throughout the EU. These sites require regeneration, which may also include soil and/or groundwater remediation treatments, before they can be beneficially reused. However, high costs and long timeframes of regeneration may hinder their reuse and redevelopment, so that greenfields may be preferred instead, causing in turn an increase in urban sprawl and land use. As for contaminated soil management strategies, one of the most applied options, at least in Southern Europe is dig and dump, i.e. the contaminated soil is excavated, transported to a landfill site and disposed of. Although this kind of approach is effective in reaching the environmental targets in terms of removing the contamination source, it is widely recognized as not sustainable in terms of land and virgin raw material use; in addition, it also promotes landfill use, which should be instead minimized according to the EU Waste Framework Directive.
Within a recent FP-7 European project HoMBRe - Holistic Management of Brownfield Regeneration, an alternative overall strategy for Brownfield regeneration was proposed based on the concept that the shift from short term local oriented problem solving to a top-down approach considering also social and economical aspects may allow to increase the sustainability of this process and promote site redevelopment and reuse. Regarding soil management, the strategy proposed relies on specifically tailored treatments to apply on site, as a tool to allow both to reduce the leaching of contaminants from the soil‚ and to obtain a product with suitable technical properties for use as construction material during the redevelopment phase of the site itself.
Within the activities of the HoMBRe project, we tested at lab-scale a treatment based on granulation and cement stabilization/solidification (S/S) for Brownfield soil slightly contaminated by metals with the aim of producing aggregates with mechanical and environmental properties suitable for reuse in construction. In particular, the selected treatment consisted in a grain size screening step in which the material was separated into two size fractions, followed by the treatment of the fine fraction by the combination of S/S with granulation. The influence on product properties of the amount and type of binder employed (cement with or without superplasticizers) and of the liquid to solid ratio was assessed. The results showed that the combined process employing 25-30% Portland cement by weight of solid product may allow to achieve a significant enlargement in particle size and a granule strength similar to that of natural limestone. The leaching behaviour of the product showed to be affected by the treatment, the release of some elements increasing due to cement addition, but overall appeared to comply with Italian requirements for reuse of non hazardous waste.
Hence, the proposed treatment appears to be effective in obtaining a product with suitable characteristics for on site reuse as aggregate, but is it really more environmentally sustainable in comparison to the dig and dump approach? This study aims at answering this question by comparing the environmental impacts resulting from the application of the proposed treatment to the Brownfield soil of the case study investigated in the lab tests as opposed to its management by dig and dump. The life cycle assessment was carried out employing the software Simapro (version 8), considering as functional unit 1 m3 of dried excavated soil to treat and including the impacts related to the production of all the reagents used in the on site treatment, as well as the avoided impacts of the production of the aggregates that may be used in substitution of virgin raw materials. As for the dig and dump scenario, impacts related to excavation, transport and landfilling were considered. As impact categories, we focused on global warming, abiotic resource depletion, human toxicity, ecotoxicity, acidification, eutrophication and land use. The results indicated that the impacts related to the proposed treatment with 30% cement were significantly higher than those resulting for dig and dump for nearly all impact categories, mostly due to the use of cement. In fact, impacts showed to decrease significantly for the treatment applied with 25% cement. Since, the binder amount and type appeared to be so crucial for the sustainability of the proposed treatment, we performed a sensitivity analysis varying the amount and type of binder to asses which combinations may provide the largest gains in terms of environmental sustainability compared to dig and dump; for example the use of 25% fly ash cement showed to yield lower impacts in all categories except global warming. The binders resulting the most sustainable from an LCA perspective could hence be tested at lab scale to verify their technical and environmental effectiveness.
Giulia Costa, Oriana Capobianco, and Renato Baciocchi, "Assessment of the environmental sustainability of a treatment aimed at soil reuse in a Brownfield regeneration context" in "Life Cycle Assessment and Other Assessment Tools for Waste Management and Resource Optimization", Professor Umberto Arena, Second University of Naples, Italy Professor Thomas Astrup, Denmark Technical University, Denmark Professor Paola Lettieri, University College London, United Kingdom Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/lca_waste/42
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