Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 142

Biochar

Biochar is organic matter that has undergone combustion under low to no oxygen conditions (such as during pyrolysis) resulting in a recalcitrant, high carbon material specifically for use as a soil amendment. Recently, fervent interest in the production of biochar to address issues of fertility, water-holding capacity, remediation, climate change mitigation, etc., led to a much greater understanding of the complexities of this potential amendment in altering soil biological, chemical, and physical properties. Rather than assume the benefit of any biochar created from any feedstock added to any soil ecosystem, concepts of matching appropriate feedstock and pyrolysis condition to soil type to achieve specific goals associated with remediation, increasing yields, decreasing greenhouse gas emission, and/or climate change mitigation emerged.

This porous sponge-like property of biochar makes it useful for many things such as the production of activated carbon filters used to purify water. Industrial production of biochar employs pyrolysis, a means of combustion without much air or oxygen and that is more efficient in that it produces little ash.

The production of biochar is a sustainable option for waste management since the char contains 50% of the original carbon which is highly recalcitrant in nature; therefore, its production helps in carbon sequestration by locking the carbon present in the plant biomass. The elemental composition and structural configuration of biochar is strongly correlated with temperature, heating rate, and residence time maintained during its production. Along with the biochar, some amount of bio-oil and gases are also produced which can be used for generation of energy and various chemicals.

Soil pH and electrical conductivity (EC) increase in soil incorporated with biochar which may be due to the presence of ash residue that is dominated by carbonates of alkali and alkaline earth metals, and some amount of silica, heavy metals, and organic and inorganic nitrogen. With its large surface area, biochar helps in increasing water holding capacity, cation exchange capacity (CEC), and microbial activity (act as its habitat) and also reduces leaching of nutrient by providing nutrient binding sites. This reduces the total fertilizer requirement of biochar-amended soil and thereby reduces environmental pollution caused by leaching of inorganic fertilizer. It also plays a vital role in increasing crop productivity. Apart from improving soil quality, biochar provides various other benefits such as (i) mitigation of greenhouse gases (such as methane, CH₄, nitrous oxide, N₂O, and carbon dioxide, CO₂), (ii) a decrease in the dissipation rate of herbicide in soil, and (iii) wastewater treatment. Due to large availability of biomass resources, biochar can be a prime product in many countries.