Sorption to soil, biochar and compost: is prediction to multicomponent mixtures possible based on single sorbent measurements?

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.

Bioretention Design Modifications Increase the Simulated Capture of Hydrophobic and Hydrophilic Trace Organic Compounds

“…We caution here that results on the practical efficacy of biochar have been mixed: although biochar amendments in soil columns have been shown to capture highly mobile compounds including PFOA, other studies have shown less strong results . In part, these different results may be related to the properties of individual biochars, considering that the specific surface area, total pore volume, aromaticity, and polarity of biochars are important for contaminant sorption. , The performance of biochars in systems with soil and compost may also be weaker than would be predicted for biochar alone due to surface and pore blockages on the biochar and due to nonlinear contaminant sorption to biochar; our results do not account for either of these processes and so may overpredict capture. The findings that suggest bioretention supplemented with biochar can effectively capture highly mobile substances (such as PFOA) should therefore be viewed as preliminary, and we recommend validating these results with column- and field-scale experiments using authentic bioretention soils.…”

“…We then added the K d,amendment term to the organic carbon sorption term already present in the model. We note that this portion of the model has not been calibrated to or evaluated against experimental data, that we assumed amendments follow a linear sorption isotherm, and that the sorption provided by amendments is additive with sorption to organic carbon. , We therefore caution that results for amended bioretention systems have considerably greater uncertainty than for unamended systems, but still provide an indication of how additional sorptive materials would impact contaminant removal.…”

Biochar particle aggregation in soil pore water: the influence of ionic strength and interactions with pyrene

“…28 It has previously been demonstrated that batch and POM methods can be used as complementary methods. 32,33 The samples were equilibrated for 24 hours following a similar sample preparation to that described above but without adding any POM sheets, then centrifuged at 1000 g for 40 minutes and 30 mL of the supernatant was collected, which was then extracted three times with hexane following the addition of the internal standard (Pyr-d10).…”

Quantitative evaluation of relationships between adsorption and partition of atrazine in biochar-amended soils with biochar characteristics

“…Biochar is a carbon-rich residue produced by the incomplete pyrolysis of biomass, 1,2 which is widely present in soil and generates potential benets for carbon sequestration, soil fertility, and immobilization and stabilization of hazardous chemicals, [3][4][5][6] due to its distinctive physicochemical characteristics, namely, large specic surface area (SSA), abundant porous structure, multifunctional groups, and strong adsorption capacity. [7][8][9][10] Inevitably, these vital characteristics of biochar can be altered once applied to the soil environment via shortterm or long-term physical, chemical, and biological processes, including natural aging, articial oxidation, and additional interactions with soil components, such as dissolved organic matter and minerals, [11][12][13][14] which, in turn, are likely to affect the adsorption behavior of contaminants, as well as their ultimate transport, fate, and bioavailability in soil. 15 In particular, studies involving the application of biochar for the immobilization of organic compounds in soil have been extensively reported.…”