Biochar remediation of soil: linking biochar production with function in heavy metal contaminated soils

Abstract

The focus of this study is on the soil physicochemical, biological, and microbiological processes altered by biochar application to heavy metal (HM) contaminated soils. The aim is to highlight agronomical and environmental issues by which the restorative capacity of biochar might be developed. Literature shows biochar can induce soil remediation, however, it is unclear how soil processes are linked mechanistically to biochar production and if these processes can be manipulated to enhance soil remediation. The literature often fails to contribute to an improved understanding of the mechanisms by which biochar alters soil function. It is clear that factors such as biochar feedstock, pyrolysis conditions, application rate, and soil type are determinants in biochar soil functionality. These factors are developed to enhance our insight into production routes and the benefits of biochar in HM soil remediation. Despite a large number of studies of biochar in soils, there is little understanding of long-term effects, this is particularly true with respect to the use and need for reapplication in soil remediation.

Effect of cornstalk biochar on phytoremediation of Pb‐contaminated soil by females and males of Populus deltoides (Salicaceae)

“…Many studies have demonstrated that biochar addition reduces soil acidity and increases soil pH through proton consumption reactions in acidic soils (Mehmood et al, 2018). This increase in soil pH can decrease HMs mobility in soil through mechanisms such as adsorption, surface complexation precipitation, and electrostatic interaction (Taraqqi‐A‐Kamal et al, 2021; Wei et al, 2022). In our study, the pH and total Pb content in soil increased significantly with the amendment of biochar (Table S1).…”

Revealing the long-term behaviour of nZVI and biochar in metal(loid)-contaminated soil: focus on Fe transformations

“…7,15,89 It is important though, to predict the long-term behaviour of soil amendments even if their effects are positive so that we can make a sustainable choice of amendment and application rate both in terms of environmental and financial efficiency. 14 The layered design that was used in this study could be a simulation of field application of soil amendments in the form of reactive barriers that are not mixed with the soil and could potentially be later removed from it. In addition, our results can assist in a future enhanced experimental design in which the sorbent layer will be more reactive.…”

“…101 Long-term studies on the efficiency of BC and the changes it provokes in the soil are still scarce, and the mechanisms involved are not yet fully explained. 14 Although a wide range of pyrolysis temperatures (400-700 °C) has been reported to produce biochar efficient for the immobilisation of Zn and Pb, 70 high temperatures (i.e., 700 °C) generally result in limited functional groups on the surface of BC and could lead to a decrease in the metal removal efficiency of BC. 102 In addition, there is evidence that the release of contaminants in untreated soil is more likely when nonspecific adsorption takes place, especially in the case of multiple element contamination.…”

“…Dovletyarova et al 106 recently showed that natural Fe oxides and BC-supported nZVI and ZVI microparticles had similar efficiency in the short time at immobilising metals in Cu-and Ni-contaminated soil. Therefore, possible modifications of the amendments could result in significantly more efficient BC-based materials for soil remediation 14 and limit the aggregation and potential toxicity of nZVI. 107 Environmental Science: Nano Paper…”

“…[3][4][5][6] However, a considerable number of studies have addressed the potential toxic effects of nZVI on living organisms, [7][8][9][10][11] while some researchers have recently focused on the possible negative impacts of BC (e.g., desorption of potentially toxic elements from BC). [12][13][14] Due to the tendency of nZVI to agglomerate, modifications (including nZVI supported by BC) have been proposed [15][16][17] to mitigate this tendency and enhance the product's remediation efficiency. Most importantly, the long-term behaviour of soil amendments is rarely studied, although there may be release of inorganic contaminants previously retained by BC 18 and nZVI.…”