Abstract
The use of biochar to stabilize soil contaminants is emerging as a technique for remediation of contaminated soils. In this study, an environmental assessment of systems where biochar produced from wood waste with energy recovery is used for remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAH) and metal(loid)s was performed. Two soil remediation options with biochar (on- and off-site) are considered and compared to landfilling. The assessment combined material and energy flow analysis (MEFA), life cycle assessment (LCA), and substance flow analysis (SFA). The MEFA indicated that on-site remediation can save fuel and backfill material compared to off-site remediation and landfilling. However, the net energy production by pyrolysis of wood waste for biochar production is 38% lower than incineration. The LCA showed that both on-site and off-site remediation with biochar performed better than landfilling in 10 of the 12 environmental impact categories, with on-site remediation performing best. Remediation with biochar provided substantial reductions in climate change impact in the studied context, owing to biochar carbon sequestration being up to 4.5 times larger than direct greenhouse gas emissions from the systems. The two biochar systems showed increased impacts only in ionizing radiation and fossils because of increased electricity consumption for biochar production. They also resulted in increased biomass demand to maintain energy production. The SFA indicated that leaching of PAH from the remediated soil was lower than from landfilled soil. For metal(loid)s, no straightforward conclusion could be made, as biochar had different effects on their leaching and for some elements the results were sensitive to water infiltration assumptions. Hence, the reuse of biocharremediated soils requires further evaluation, with site-specific information. Overall, in Sweden's current context, the biochar remediation technique is an environmentally promising alternative to landfilling worth investigating further.
Highlights
Contamination of soils from human activities is one of the most significant environmental problems in the contemporary world (Zama et al, 2018)
The consumption of biodiesel in Scenario 1 (S1) is more than 6 times higher than in Scenario 2 (S2) and Scenario 3 (S3) because of the transportation of wood waste from the waste management (WM) facility to the incinerator by trucks running on biodiesel
Another finding is that in S1 and S2, virgin material is used for backfilling, something that is avoided in S3 thanks to on-site soil remediation
Summary
Contamination of soils from human activities is one of the most significant environmental problems in the contemporary world (Zama et al, 2018). An extensively used method for handling soil contaminated with e.g. heavy metals and persistent organic pollutants is to excavate and landfill the contaminated soil, and backfill the excavated area with clean material This technique is problematic due to the scarcity of landfill space, high energy requirements, and limited availability of natural resources for backfill. A wide range of remediation techniques have been developed, such as bioremediation, chemical oxidation, steam injection, or soil washing (de Albergaria and Nouws, 2016). These techniques are usually optimised for one or a few specific contaminants, and can be implemented either on-site or off-site (Busset et al, 2012; Lemming et al, 2010a). Efforts are being made to develop new, more efficient, remediation techniques, with lower costs and lower environmental impacts
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