Advances in research on the use of biochar in soil for remediation: a review

Purpose: Soil contamination mainly from human activities remains a major environmental problem in the contemporary world. Significant work has been undertaken to position biochar as a readily-available material useful for the management of contaminants in various environmental media notably soil. Here, we review the increasing research on the use of biochar in soil for the remediation of some organic and inorganic contaminants.  Materials and methods: Bibliometric analysis was carried out within the past 10 years to determine the increasing trend in research related to biochar in soil for contaminant remediation. Five exemplar contaminants were reviewed in both laboratory and field-based studies. These included two inorganic (i.e., As and Pb) and three organic classes (i.e., sulfamethoxazole, atrazine, and PAHs). The contaminants were selected based on bibliometric data and as representatives of their various contaminant classes. For example, As and Pb are potentially toxic elements (anionic and cationic, respectively), while sulfamethoxazole, atrazine, and PAHs represent antibiotics, herbicides, and hydrocarbons, respectively.  Results and discussion: The interaction between biochar and contaminants in soil is largely driven by biochar precursor material and pyrolysis temperature as well as some characteristics of the contaminants such as octanol-water partition coefficient (KOW) and polarity. The structural and chemical characteristics of biochar in turn determine the major sorption mechanisms and define biochar’s suitability for contaminant sorption. Based on the reviewed literature, a soil treatment plan is suggested to guide the application of biochar in various soil types (paddy soils, brownfield, and mine soils) at different pH levels (4–5.5) and contaminant concentrations ( 50 mg kg−1).  Conclusions: Research on biochar has grown over the years with significant focus on its properties, and how these affect biochar’s ability to immobilize organic and inorganic contaminants in soil. Few of these studies have been field-based. More studies with greater focus on field-based soil remediation are therefore required to fully understand the behavior of biochar under natural circumstances. Other recommendations are made aimed at stimulating future research in areas where significant knowledge gaps exist

Experimental evidence for sequestering C with biochar by avoidance of CO2 emissions from original feedstock and protection of native soil organic matter

There is a need for further studies to compare the decomposition of biochar to that of the original feedstock and determine how these amendments affect the cycling of native organic matter (NOM) of different soils to improve our understanding of the resulting net C sequestration potential. A 510-days incubation experiment was conducted (i) to investigate the evolution of CO2 from soils amended with either fresh corn stover (CS) or with biochars produced from fresh CS at either 350 (CS-350) or 550 degrees C (CS-550), and (ii) to evaluate the priming effect of these amendments on NOM decomposition. Two soil types were studied: an Alfisol and an Andisol, with organic C contents of 4% and 10%, respectively. Except for the controls (with no C addition), all treatments received 7.18t Cha(-1). We measured C efflux in short-term intervals and its isotopic signature to distinguish between C evolved from C-4 amendments and C-3-dominated NOM. Emission rates were then integrated for the whole time period to cover total emissions. Total CO2-C evolved from the original C in fresh CS, CS-350 and CS-550 was greater in the Andisol (78%, 13% and 14%) than in the Alfisol (66%, 8% and 7%). For both soils, (i) no significant differences (P>0.05) were observed in the rate of CO2 evolution between controls and biochar treatments; and (ii) total accumulated CO2 evolved from the uncharred amendment was significantly higher (P0.05) net priming effect was observed. A C balance indicated that the C lost from both biochar production and decomposition broke even' with that lost from fresh residue decomposition after <35weeks. The break-even' point was reached earlier in the Andisol, in which the fresh CS mineralizes faster. These results provided experimental evidence for the potential of biochar to sequester C and avoid CO2 emissions from original feedstock while protecting native soil organic matter

The chemical composition of native organic matter influences the response of bacterial community to input of biochar and fresh plant material

Aim To investigate how the chemical composition of native organic matter of two contrasting soils varies with inputs of biochar and fresh material (including plant roots) and how these underlying changes influence microbial community structure. Methods Corn stover (CS) and CS-derived biochars produced at 350 °C and 550 °C were applied at a dose of 7.2 t C ha−1 to two contrasting soils—an Alfisol and an Andisol. After 295 days of incubation, two undisturbed subsamples from each pot were taken: (i) in one, lucerne (Medicago sativa L.) was seeded (plant study, P) and (ii) in the other, the incubation was continued without the plants (respiration study, R); all subsamples were incubated for an additional 215 days. Soils without amendments were used as controls. At the end of the incubation (510 days), their bacterial community profiles were characterised using ARISA and the molecular composition of soil organic matter (SOM) was investigated by pyrolysis-GC/MS. Results There were significant interactions between soil type, study type (P or R) and organic amendment. Organic amendments influenced overall SOM composition with microbial community response being mainly influenced by soil type but also strongly affected by the presence or absence of plants. For a specific soil type, ≥ 40 % of total variation in bacterial community ordination could be explained by the molecular composition of SOM. Conclusions The molecular composition of SOM is proposed as an important factor influencing the microbial response to organic amendments, including biochar