Abstract
Amendment with biochar and/or compost has been proposed as a strategy to remediate soil contaminated with low levels of polycyclic aromatic hydrocarbons. The strong sorption potential of biochar can help sequestering contaminants while the compost may promote their degradation. An improved understanding of how sorption evolves upon soil amendment is an essential step towards the implementation of the approach. The present study reports on the sorption of pyrene to two soils, four biochars and one compost. Detailed isotherm analyzes across a wide range of concentration confirmed that soil amendments can significantly increase the sorption of pyrene. Comparisons of data obtained by a classical batch and a passive sampling method suggest that dissolved organic matter did not play a significant role on the sorption of pyrene. The addition of 10% compost to soil led to a moderate increase in sorption (<2-fold), which could be well predicted based on measurements of sorption to the individual components. Hence, our result suggest that the sorption of pyrene to soil and compost can be relatively well approximated by an additive process. The addition of 5% biochar to soil (with or without compost) led to a major increase in the sorption of pyrene (2.5–4.7-fold), which was, however, much smaller than that suggested based on the sorption measured on the three individual components. Results suggest that the strong sorption to the biochar was attenuated by up to 80% in the presence of soil and compost, much likely due to surface and pore blockage. Results were very similar in the two soils considered, and collectively suggest that combined amendments with compost and biochar may be a useful approach to remediate soils with low levels of contamination. Further studies carried out in more realistic settings and over longer periods of time are the next step to evaluate the long term viability of remediation approaches based on biochar amendments.
Highlights
Biochar is a carbon rich material produced by the pyrolysis of a variety of feedstock at temperatures below 700 C (EBC, 2012; IBI, 2015)
The biochars produced from miscanthus sorbed significantly more pyrene than biochars produced from soft wood, which was unexpected in view of the greater OC%, Cs Cs
Detailed isotherm analyzes across a wide range of concentration confirmed that soil amendment with compost and biochar can significantly increase the sorption potential towards pyrene
Summary
Biochar is a carbon rich material produced by the pyrolysis of a variety of feedstock at temperatures below 700 C (EBC, 2012; IBI, 2015). Two recent studies have suggested that combining biochar and compost amendments to soils contaminated with polycyclic aromatic hydrocarbons may be successful to significantly reduce toxicity to soil organisms e.g. Caenorhabditis elegans (Bielskaet al., 2017), while avoiding the full inhibition of the degradation process (Sigmund et al, 2018). Both studies suggested that changes in toxicity and degradation occurred through changes in the contaminant sorption, but details regarding the process were limited to data obtained at relatively high concentrations and/or in the presence of multiple contaminants. More detailed investigations into the sorption process are needed to support the future development of remediation approaches combining biochar and compost amendments
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