Enhanced Immobilization of Polycyclic Aromatic Hydrocarbons in Contaminated Soil Using Forest Wood-Derived Biochar and Activated Carbon under Saturated Conditions, and the Importance of Biochar Particle Size

Abstract

Leaching behavior of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) can be altered in the presence of organic amendments through enhanced sorption of PAHs to the amended soil. The aim of the present study was to investigate the influence of biochar in two forms (i.e., crushed and pulverized), and granular activated carbon on immobilization and leaching behavior of selected PAHs from contaminated soil into water using the column leaching test. The influence of biochar particle size on leaching behavior of PAHs in biochar-amended soil was also evaluated for the first time in this study. Results showed relatively high initial concentrations of naphthalene, fluorene, and pyrene for unamended column (B1). Strong sorption of all PAHs to soil was observed in this study. At the end of the experiment less than one percent of the solid phase content of the sum of PAHs was released into water in columns B3 and B4. Change in pH due to the application of organic amendments did not affect PAH leaching results. The addition of pulverized biochar and granular activated carbon to soil remarkably reduced mobilization and leaching of the studied PAHs in most cases; however, higher molecular weight PAHs (i.e., pyrene, benzo(b)fluoranthene, and indeno(1,2,3-cd)) were mobilized in the presence of crushed biochar in soil. The controlling role of biochar particle size on mobilization and release of PAHs in soil was observed. The application of pulverized biochar and activated carbon increased colloid content of the column effluents while reducing their dissolved organic carbon (DOC) content, suggesting a more significant role of colloid-facilitated transport than DOC-associated transport of PAHs in their leaching from carbon-amended soils, particularly for higher molecular weight PAHs. Based on the obtained results, pulverized biochar and granular activated carbon demonstrated promising and comparable performance in immobilizing PAHs in soil and reducing their leaching from soil into water through enhanced sorption of PAH compounds, which is markedly favorable in terms of soil remediation.

Trial by Fire: On the Terminology and Methods Used in Pyrogenic Organic Carbon Research

“…And soil translocation, erosion, leaching, and other hydrologic/climatic-related processes of a region are likely to act to mobilize both pyOM and non-pyOM in similar ways (Hilscher and Knicker, 2011;Jien and Wang, 2013), though not necessarily to equal extents (Rumpel et al, 2009). Finally, it has been suggested that pyC mobilization may occur via association with other OM in dissolved or perhaps colloidal (Zand and Grathwohl, 2016;Kumari et al, 2017) form, but the controlling mechanisms are still unknown (Wagner et al, 2017).…”

Use of biochar as a remediation technique for hydrocarbon contaminated soils in Peru

“…Biochar also reduces the leaching of hydrocarbons in soils. Zand and Grathwohl (2016) confirmed that biochar is a rich sorbent and demonstrated that its particle size is inversely proportional to the hydrocarbon immobilization rate, with greater effectiveness when the powdered amendment is used. According to Sander and Pignatello, the sorption of hydrocarbons through the use of biochar is due to the presence of electron donor-acceptor interactions through π-π radicals on the surface of the amendment and the hydrocarbon; with biochar the donor and hydrocarbon the electron acceptor.…”

Constraints and Drivers of Dissolved Fluxes of Pyrogenic Carbon in Soil and Freshwater Systems: A Global Review and Meta‐Analysis

“…Many of these reported positive correlations between dPyC with DOC and source PyC concentration (Bi et al, 2018;Güereña et al, 2015;Jones et al, 2019). In contrast, several studies reported a reduction in DOC export after biochar or charcoal amendment (e.g., Abdelrahman et al, 2018;Braun et al, 2020;Zand & Grathwohl, 2016), suggesting initial sorption of OM to the added PyC surface. Furthermore, many of these papers noted or measured variability in time post-fire or post-addition of charcoal as factors in leaching of PyC (e.g., Bi et al, 2018;Jones et al, 2019;Santos et al, 2017), highlighting the need for investigation on the controls on the timing of post-fire dPyC fluxes.…”