Effect of ageing on the properties and polycyclic aromatic hydrocarbon composition of biochar

Abstract

The influence of ageing on biochar properties has been investigated by comparing three fresh biochars with biochars artificially aged by either HO thermal oxidation or horseradish peroxidase enzymatic oxidation. In addition, a field-aged counterpart for one of the biochars was recovered from an agricultural field site, four years after application. Biochar properties, including surface areas and pore volumes (derived by N and CO physisorption) and elemental compositions, showed only minor changes following both artificial and field ageing, indicating high biochar stability. Concentrations of the 16 US EPA PAHs were measured in all of the biochars and a contaminant trap was used to investigate the effect of ageing on their bioaccessibility. The concentrations of total and bioaccessible PAHs ranged from 4.4 to 22.6 mg kg and 0.0 to 9.7 mg kg, respectively. Concentrations of the 16 US EPA PAHs decreased following field ageing, but the proportion of low molecular weight PAHs increased. The observed changes in PAH composition with field ageing can be explained by uptake from the surrounding soil and intra-biochar transfer processes. To better understand changes in PAH composition with ageing, an additional broad range of alkylated PAHs was also analyzed in selected samples. Our results show that the tested artificial ageing protocols are unable to approximate the changes in PAH composition resulting from field ageing. Nevertheless, total and bioaccessible PAH concentrations decreased for both artificially and field-aged biochars, indicating that biochars release PAHs when they are freshly produced and that the risk of PAH release decreases with ageing.

Environmental behavior of engineered biochars and their aging processes in soil

“…Biological aging led to the greatest reduction efficiency. Another study also confirmed that PAHs concentration in biochars decreased after 4 years field aging process (Sigmund et al 2017). The authors referred to the sorption by the surrounding soil of low molecular weight PAHs.…”

Environmental transformation of natural and engineered carbon nanoparticles and implications for the fate of organic contaminants

“…Many pCNPs -especially wildfire charcoal and biochars-contain intrinsic micropore networks which can result in strong sorption hysteresis exceeding that of eCNPs, making these pCNPs potentially more effective contaminant vectors than eCNPs. Although preliminary results indicate that the micropore and mesopore size distributions of certain types of biochar may remain similar after transformation in the field, 70,146 this observation cannot be extrapolated to other types of biochar, soot, or wildfire charcoal, which may be transformed under different conditions in the natural environment (e.g., under different temperatures, water saturation, or pH).…”

“…132,137 Organic contaminants sorbed by CNTs, fullerenes, fossil coal, and biochar are generally not very bioaccessible because of their high contaminant-binding capacities. 116,144,145 However, when comparing these materials, which are generally produced under controlled conditions, with their counterparts from unintentional emissions (e.g., soot, 24,25 biochar produced under poorly controlled conditions, 146 or wildfire charcoal 29 ), the sorption and release of organic contaminants can differ considerably. To derive conclusions for contaminant release from soot, biochar, and wildfire charcoal on the basis of findings for eCNPs is therefore not advisable, as additional factors need to be taken into account.…”

The Impact of Biochar Incorporation on Inorganic Nitrogen Fertilizer Plant Uptake; An Opportunity for Carbon Sequestration in Temperate Agriculture

“…The Biochar had an H/Corg ratio of 0.3 and a PAH content (∑ 16 EPA PAH) of 9 mg kg −1 [35]. Further details of the Biochar are described in Sigmund et al, 2017 [36]. Biochar was applied once to the field at a dry mass rate of 0 and 72 t ha −1 in March 2011 and incorporated to a depth of 10 cm using a rotary hoe.…”