Biochar Production, Modification, and Its Uses in Soil Remediation: A Review

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Abstract

Soil remediation is the act of removing or reducing the availability of contaminants from soil. In the case of agriculture, soil remediation targets the removal of pollutants, including residual pesticides/herbicides, hydrocarbons, and toxic heavy metals. This is often done by chemical treatments with multiple washes or excavation of soils, which are costly and time-consuming. Therefore, finding cheaper, less time-consuming remediation methods is highly desirable. In this review, we will examine the addition of biochar as an effective method of soil remediation. Biochar is a carbon-rich material derived from burning biomass in an oxygen-limited environment with benefits such as high cation exchange capacity, large surface area, neutral to alkaline pH, and some nutritional content. Biochar can also be a sanctuary for naturally occurring microbes and can be inoculated with specific microbes for contaminant breakdown. The physical and chemical characteristics of biochar combined with biological activity can help bind and promote the degradation process of these contaminants without the need to use hazardous chemicals or remove a large amount of soil. Biochar, and the microbes they house, can bind these contaminants through electrostatic attraction, sorption, precipitation, and bioaccumulation, reducing their availability to the surrounding environment. However, the characteristics of biochar and its biological activity can vary depending on the feedstock, pyrolysis temperature, and time the mass is heated. Therefore, some of these traits can be modified through pre or post-treatments to suit their intended use, allowing for biochar to be made for specific contaminants. This review hopes to increase interest in biochar research to fill in missing gaps of information that could make biochar production cheaper and more consistent, as it offers a greener way to clean up contaminants in soil.

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Dynamic molecular structure of plant biomass-derived black carbon (biochar).

Marco Keiluweit, Peter Nico, Mark Johnson … (2010)

Char black carbon (BC), the solid residue of incomplete combustion, is continuously being added to soils and sediments due to natural vegetation fires, anthropogenic pollution, and new strategies for carbon sequestration ("biochar"). Here we present a molecular-level assessment of the physical organization and chemical complexity of biomass-derived chars and, specifically, that of aromatic carbon in char structures. Brunauer-Emmett-Teller (BET)-N(2) surface area (SA), X-ray diffraction (XRD), synchrotron-based near-edge X-ray absorption fine structure (NEXAFS), and Fourier transform infrared (FT-IR) spectroscopy are used to show how two plant materials (wood and grass) undergo analogous but quantitatively different physical-chemical transitions as charring temperature increases from 100 to 700 degrees C. These changes suggest the existence of four distinct categories of char consisting of a unique mixture of chemical phases and physical states: (i) in transition chars, the crystalline character of the precursor materials is preserved; (ii) in amorphous chars, the heat-altered molecules and incipient aromatic polycondensates are randomly mixed; (iii) composite chars consist of poorly ordered graphene stacks embedded in amorphous phases; and (iv) turbostratic chars are dominated by disordered graphitic crystallites. Molecular variations among the different char categories likely translate into differences in their ability to persist in the environment and function as environmental sorbents.

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Preparation, modification and environmental application of biochar: A review

Jianlong Wang, Shizong Wang (2019)

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Biochar physicochemical properties: pyrolysis temperature and feedstock kind effects

Agnieszka Tomczyk, Zofia Sokołowska, Patrycja Boguta (2020)

Biochar is a pyrogenous, organic material synthesized through pyrolysis of different biomass (plant or animal waste). The potential biochar applications include: (1) pollution remediation due to high CEC and specific surface area; (2) soil fertility improvement on the way of liming effect, enrichment in volatile matter and increase of pore volume, (3) carbon sequestration due to carbon and ash content, etc. Biochar properties are affected by several technological parameters, mainly pyrolysis temperature and feedstock kind, which differentiation can lead to products with a wide range of values of pH, specific surface area, pore volume, CEC, volatile matter, ash and carbon content. High pyrolysis temperature promotes the production of biochar with a strongly developed specific surface area, high porosity, pH as well as content of ash and carbon, but with low values of CEC and content of volatile matter. This is most likely due to significant degree of organic matter decomposition. Biochars produced from animal litter and solid waste feedstocks exhibit lower surface areas, carbon content, volatile matter and high CEC compared to biochars produced from crop residue and wood biomass, even at higher pyrolysis temperatures. The reason for this difference is considerable variation in lignin and cellulose content as well as in moisture content of biomass. The physicochemical properties of biochar determine application of this biomaterial as an additive to improve soil quality. This review succinctly presents the impact of pyrolysis temperature and the type of biomass on the physicochemical characteristics of biochar and its impact on soil fertility.